1. Needle-nose pliers for zip tie trimming.
    • Needle-nose pliers for zip tie trimming.

    • 3mm Allen key for M5 screws

    • 2.5mm Allen key for M3 screws

    • 2mm Allen key for nut alignment

    Some additions I found to help make the build go better: long T-handled 3mm & 2.5mm hex wrenches, tweezers for holding small parts, plastic-face mallet for easier X-axis rod assembly, plastic spudger to manipulate wires without damaging, needle file for cleaning out holes in printed parts, exacto knife for cleaning threads in trapezoidal nuts.

    Scott Story - Reply

    Diagonal cutters for trimming cable ties. It would be nice if the kit included either 3D printed or metal stamped open end wrenches of the sizes mentioned in the comment above. Getting precise tightening of the small nuts is difficult with the supplied needlenose pliers and is prone to damaging the nut.

    Kris Boyle - Reply

    I agree with others that a set of hex drivers , along with a couple of ball ends for quick light angular tightening, will speed things up. And, a good curved end hemostat for placing small nuts into tight captured impressions; then open them slightly, placing each jaw on the edge of the nuts and, using your other hand press down on the jaws to fully seat the nut.. Also, the nylok nuts seem to take a 5.5mm socket driver. Luckily, I found an old 7/32” laying around that worked fine.

    Stephen Gomes - Reply

    Thank you for your comment Stephen, will see what I can do about it.

    Tomáš - Reply

    Check the comments on step 10 before you tighten the screws.

    Gabriel Anzziani - Reply

  2. Prepare following parts to build the YZ frame:
    • Prepare following parts to build the YZ frame:

    • Aluminum extrusions (4x)

    • Aluminum frame (1x)

    • M5x16r screw (16x)

    • You can tighten the M5x16r with included Allen key or with a Torque Wrench. Recommended torque is 4.5 N.m (40 lb-in).

    The M5x16 screws are labeled as “M5x16r” on the “2. Y-AXIS” pack, the name on this instruction should probably be updated to match what the pack says.

    Kevin Gallagher - Reply

    Hi Kevin, thank you. Information updated.

    Jakub Dolezal -

    The inner smaller bag is labeled 3/2. Y-Axis MK3.

    Neal Tibrewala - Reply

    What type of extrusion are used? V-Slot 2020?

    Googliola - Reply

    Hi, we are using aluminum extrusions PAR-HWR-MK3-3030

    Jakub Dolezal -

    What is the hardware supplied made from (Steel, stainless(304,316))?

    Chris Barney - Reply

    The partlist says Aluminium frames and extrusions. I guess the screws are just steel with a coating (not stainless steel)

    Pascal Roobrouck -

    For those that don’t have Torque Wrench, can you describe how tight is “4.5 N.m”? Is it “really tight”, “kinda tight”, “crazy tight”?

    Seriously, I am curious how to gauge that without the, well, gauge. :)

    Gene Dahilig - Reply

    More of a really tight. Unless you have a gorilla grip the screw seems to show when its good. The tip of your thumb and side of your pointer finger should be uncomfortable after tightening all of them. There should be a deflection in the long side of the supplied Allen wrench. You can’t get it tight enough with the small side of the wrench in your hand. Hope that helps.

    Chris Barney -

    Hi Gene, the entire printer can be tightened with included Allen keys. The applied force should be great enough to tighten the screw to the surface, but you shouldn't be “wrestling” with the printer, nor feeling pain in your hands.

    Jakub Dolezal -

    Well, my arms and shoulders hurt on a torque wrench at 4.5 Nm but maybe it’s because I don’t go to the gym :)

    Ayberk Özgür -

    I actually stripped a few of the hex screws while tightening them to 4.5 Nm with a torque wrench. Luckily there was some extra ones in the spares bag. I also ordered some higher quality (12.9 grade) screws to replace all of them later.

    Viljami Pirttimaa -

    It would be nice if there was a page before this showing all of the components for the entirety of the Step. I prefer to get everything for a Step organised at the beginning of the step rather than pulling them out by subassembly such as the YZ frame here.

    Kris Boyle - Reply

    Are there any other bolts in the assembly that should be torqued? I’ve read through the entire manual and this is the only mention I’ve seen.

    Brian Dobson-Lewis - Reply

    The M5x16 screws (in total 32 of them) are now in a small bag labeled: “3/2 Y-AXIS MK3”

    HugoB - Reply

    Hi there Hugo, thank you for your comment will check it out.

    Tomáš - Reply

    • Take the LONGER aluminum extrusions and place them next to the frame.

    • Make sure the engraved PRUSA logo on the frame (top left) IS VISIBLE!

    • Note: screws are inserted from the opposite side of the frame. If you need to manipulate with the frame, make sure the extrusions are on the correct side.

    • Ensure you are using the correct holes, see the second picture. Use the M5 screws to connect extrusions to the frame. Tighten the screws with the Allen key just slightly!

    • Now, tighten the screws fully, but ON A DIAGONAL, see the last picture. As soon as you finish the first, tighten the second pair. Then proceed to the second long extrusion.

    I see there’s no mention of locking washer, is this because theres no perceived need/cost savings, or? I would assume that the frame and bolts are subject to vibration and would need after tightening over time?

    Robert Hooper - Reply

    I assume there will be issues with vibration over time. I used loctite blue (removeable) for structural metal/metal connections.

    Steven Underwood -

    Hi Robert, I discussed this with devs some time ago and according to our tests, it was ok. You can recheck them each time doing maintenance, but it should be ok.

    Jakub Dolezal -

    Locking washers have been shown to provide little or no resistance to vibration. (You can verify this with reliable sources, such as the NASA fastener manual.) The only reliable methods to secure fasteners are threadlocking adhesives (e.g. Loctite), tab washers, safety wiring, and in some cases mechanical thread deforming fasteners.

    Guido Kimble -

    Hi Guido, thanks for the additional information :) Using adhesive isn't recommended since you might need to adjust the frame geometry later on.

    Jakub Dolezal -

    I would like to see torque values so I can tighten just right.

    Robert Burkhalter - Reply

    I made a mistake in this part. I confused the logo with the stick with a logo in the back face of the frame. The logo is difficult to see. This is confusing, the stick is located also at top left on the back face. Could you place the stick in other localization? Now I have to remount the printer to turn the frame at the correct side

    Pelms - Reply

    Hi Pelms, changing the sticker position won’t be easy, I will adjust the text instead.

    Jakub Dolezal -

    Reference values for a torque wrench would be nice.

    Emre Erokyar - Reply

    I would also like to see a torque range specified. I’m guessing something in the 4N-m range would be sufficient, but confirmation would be nice.

    Chris H - Reply

    Red text makes it easy to be alerted.

    Would it be possible to print that text in the printed assembly instructions in red too?

    Wolfgang Peters - Reply

    Hi Wolfgang, I'm working on it. This setting must be changed by a company providing this manual software.

    Jakub Dolezal -

    I too would like to see torque values.

    Randy - Reply

    I initially followed all instructions until step 10 and noticed some wobble on my frame. I untightened all 32 screws, then put the frame on a flat surface, then sequentially tightened all screws just a little bit, and kept repeating until they were all tight.

    Gabriel Anzziani - Reply

    I am doing this step now , the manual says 40 in/lbs this is a lot in my opinion , as soon as i go over 20in/lbs the frame distorts , to bring it back level i need to do 35 on the bottom 2 and 25 on the top 2 , I am using a CDI tension screwdriver

    Ron Peno - Reply

    really watch this step carefully and I would say check the online version because in the printed manual the engraved logo can’t be seen, so I thought I had to have the grey sticker toward me. resulting in the fact the printer has been build completely backwards.

    now I have to start over again because I can’t place the power unit, unless it is save to unscrew the plastic part of the power unit and put it back the other way around(turn it 180 degrees)

    Peter - Reply

    Ant thoughts on using Loctite threadlocker on these screws? I know my MK2 can really vibrate sometimes, I’d hate to have increasing bad prints and not know it’s these screws loosening sometime in the future.

    Ybl84f1 - Reply

    • Take the SHORTER aluminum extrusions and place them next to the frame.

    • Short extrusions must be placed on the side, where engraved PRUSA logo on the frame (top left) IS NOT VISIBLE.

    • Note: screws are inserted from the opposite side of the frame. If you need to manipulate with the frame, make sure the extrusions are on the correct side.

    • Ensure you are using the correct holes, see the second picture. Use the M5x16 screws to connect extrusions to the frame. Tighten the screws just slightly!

    • Now, tighten the screws fully, but ON A DIAGONAL, see the last picture. As soon as you finish the first, tighten the second pair. Then proceed to the second short extrusion.

    looks actually easier if you swapped steps 3 n 4 because the long extrusions interfere the allen key of the closer M5 screws on the short extrusions when tightening them,….

    Alex Tutusaus - Reply

    Hi Alex,

    We've tested several approaches, but thanks for the feedback. I will recheck it again.

    Jakub Dolezal -

    Better to pitch the allen wrenches all together and get a quality set of hex screw drivers.

    Murray Foster - Reply

    Any guidance from the devs on torque settings on the screws?

    Martin Stoufer - Reply

    Hi Martin, no torque is defined for the tightening. I will talk to the devs.

    Jakub Dolezal -

    Thanks Jakub. I’ve seen a few posts across the forum from wrench heads like myself that would feel better with points of assembly that did call for specific torque settings on bolts/screws. This could even be a range of min torque (enough to seat the bolt) and max (bolt will break, material will strip) From that we can start to get a better idea on how much “a quarter turn after seating” really means. Keep up the great work, we are all pulling for you!

    Martin Stoufer - Reply

    Thanks Martin ;)

    Jakub Dolezal -

    I used a power screwdriver for the insertion, but not the tightening. Did not have a 3 mm hex bit, but a 1/8 square one fit , but would not apply any force with it.

    Henry Casson - Reply

    At this step (and with the long extrusions), I’ve put the frame flat on a table with the extrusions hanging down over the table edge. Then when you tighten the screws it pulls the extrusions upwards uniformly, helps a lot to get it flush.

    Werner Marais - Reply

    • Before we proceed further, let's make a final check. IT IS VERY IMPORTANT to have extrusions on the correct side of the frame.

    • Long extrusions - must be on the side of the frame with the Prusa logo, also ensure longer extrusions are closer together.

    • Short extrusions - must be on the side of the frame without the Prusa logo, also ensure shorter extrusions are further away from each other.

    Would make sense to me to do step #11 now (anti-vibration feet) BEFORE adding the end pieces.

    Mike Womer - Reply

    Hi Mike, it is not possible as you need to check the geometry first.

    Jakub Dolezal -

    At this point (after all the screws are tightened) is it OK for the assembly to wobble side-to-side on the main frame?

    David S. Warner - Reply

    Stupid question, sorry. The frame will wobble as expected since the end pieces haven’t been put on yet. (Should have read ahead. :-)

    David S. Warner -

    Hi David, no problem ;) We are trying to include all steps necessary, so even the geometry check is included.

    Jakub Dolezal -

    Through my years of being in the R/C hobby I’ve learned a trick that helps with tightening screws and comes in handy for those that don’t have a torque wrench. When tightening the screws you can feel the threads lock together when they are properly tightened. I’ts hard to explain in writing but to check if your screws are tighten enough, loosen one and feel if has a slight “pop” as it breaks loose. Do this with all of your screws a few times and you should be able to feel them “lock up” when tightened properly. My other MK3 has over 300 hours on it and not one has come loose. Doing should keep you from over tightening and warping the frame while keeping them from backing out from vibrations. It does take a bit of practice to get a feel for it but isn’t too hard to master.

    Paul Betz - Reply

    • Prepare following parts to assemble the front and rear plates:

    • Front plate (1x)

    • Rear plate (1x)

    • M5x16r screw (16x)

    • You can tighten the M5x16r with included Allen key or with a Torque Wrench. Recommended torque is 4.5 N.m (40 lb-in).

    It would be nice if this also mentioned the PSU holders needed in step 8

    Ryan Peters - Reply

    Hi Ryan, thanks for the suggestion ;)

    Jakub Dolezal -

    Same thing as in step 2, the M5x16 screws are labelled M5x16r.

    Martin Masson - Reply

    Thank you, I was wondering the same thing.

    Travis Howard -

    Hi Martin, thanks, corrected.

    Jakub Dolezal -

    I was sent 2 rear plates and NO front plate. So I am stopped right here. Yesterday I posted this info to the contact form. I also did the Chat thing. The Chat guy said to email the info@prusa3d. I did that. This morning there was no acknowledgement of my problem. So I Chat again. they said that it takes a day or so to get to my emails? He said that he would make sure the part went out today. But I have received no confirmation. Please help. BTW I would be willing to pay for expidited shipping. Also if you have an stl file of this part or a print with dimensions, I could print a front plate out till yours get here. Pls let me know what is going on…. It’s frustrating to not have the part and have the kit spreak all over my workbench with nothing to do. I need a front plate/ ( order 182128943) Thanks

    Bob Keenan - Reply

    Hi Bob, I'm sorry for the error in the kit. My colleagues from the support are doing their best to solve all your requests as soon as possible. Let me know if there is anything else I can help with.

    Jakub Dolezal -

    • Rotate the frame with longer extrusions towards you.

    • Place the front plate on the extrusions and secure it with M5x16r screws, DON'T TIGHTEN them yet!

    • Now, tighten the screws fully, but ON A DIAGONAL, see the second picture. As soon as you finish the first, tighten the second pair. Then proceed to the second long extrusion.

    I used the included filament box placed on the extrusions near the back plate. This helped keep the back down while tightening the front. Helped keep the frame flat. Could include it as a tip.

    Joe V - Reply

    For all metal on metal joints (screws into metal) I would recommend blue (removable) locktite thread locker.

    Jim O'Keane - Reply

    • This is a very IMPORTANT step! Incorrect placement of PSU holders will lead to issues later.

    • For the following step please prepare:

    • PSU holders M3nE (2x)

    • Take the YZ frame and rotate it with the shorter extrusions towards you.

    • Place the PSU holders in the extrusion, ensure it is the correct extrusion. See the picture.

    • The exact position of the PSU holders doesn't matter, we will adjust them later.

    If you use t-nuts instead slot nut it doesn’t matter if you miss the PSU holders now.

    Heiko Schultz - Reply

    Hi Heiko, slot nuts were chosen by our devs for certain reasons, but I will forward to them your suggestion ;)

    Jakub Dolezal -

    The PSU holder is part M3nE

    Brandon Oprendek - Reply

    Brandon you're right, description updated.

    Jakub Dolezal -

    My two single PSU holders are physically different from each other in the sense that the screw head beds in the threaded openings, on the outer side, are different in diameter / depth. I cannot tell now whether this matters. It would be good to provide instructions which one goes in first, if that matters.

    Stephan Kyutchukov - Reply

    Hi Stephan, both PSU holders should be the same. Please check you can insert screw M3x10 in both.

    Jakub Dolezal -

    Mine also look different. It appears that on the underside of the holder (the part that is facing down when the holder is placed in the slot) the countersink for the screw hole is deeper on one holder than on the other. Because these face down I would assume there isn’t an issue. I think the only reason those sides are counter sunk at all is to remove the flashing from the edges of the hole after it’s drilled and tapped.

    Maximus McNobblybits -

    I forgot the PSU holders because they were’nt in an overview photo like in step 2 and step 6. as I expected. Fortunately, I didn’t have to deassemble the whole printer, I could remove the smaller extrusion and insert the PSU holders.

    Edwin Martin - Reply

    +1 PSU holders in parts list photo

    It would be good to add the PSU holders to the overview photo. Especially since you show all 16 m5 screw, but only use 8 before switching to PSU holders in PSU holders. Followed by the last 8 m5 screws.

    Still, I am very impressed so far with the detailed instructions. Great job.

    Gene Dahilig -

    Can you please provide a part number and/or a supplier for these slot nuts? I would like to buy some more.

    Gavin Nicely - Reply

    Hi Gavin, I’m sorry I don’t have the list with me. Please visit our eshop shop.prusa3d.com and ask my colleagues via live-chat. Thanks

    Jakub Dolezal -

    Place the PSU holders in the extrusion, ensure it is the correct one.

    Perhaps change “the correct one” to “the correct extrusion”? I spent several minutes trying to figure out which holder was the correct one, lol.

    tim - Reply

    Hi Tim, interesting point. I will change the description ;)

    Jakub Dolezal -

    The red warning at the top is missing the word “a” – it should read: “This is a very IMPORTANT step!” :)

    Joe Weber - Reply

    Hi Joe, thanks, missing “a” added ;)

    Jakub Dolezal -

    I have a slight amount of flash obstructing the edge of the slide grooves on one of the PSU holders. I managed to remove it with the enclosed pliers, but it’s a little sharp. Will this be an issue?

    Daniel Kilboy - Reply

    How am I supposed to get the PSU holders on my own clone? Cant find the files and cant find it on the internet.

    Abitamim Bharmal - Reply

    following the manual it turned out the psi holders were placed at the wrong side.

    or it is my lack of English or it is not quite clear were the place them. end of story everything could be de-built to switch the holders to the other side.

    Peter - Reply

    • Ensure the frame with shorter extrusions is rotated towards you.

    • Place the rear plate on the extrusions and secure it with M5x16r screws, DON'T TIGHTEN them yet!

    • Now, tighten the screws fully, but ON A DIAGONAL, see the second picture. As soon as you finish the first, tighten the second pair. Then proceed to the second short extrusion.

    Make sure you have enough M5x16 screws. I was shorted 4 screws and had to use all of the available spares.

    Paul Betz - Reply

    Hi Paul, thank you for the feedback. I will forward this to the production team.

    Jakub Dolezal -

    • Before you proceed further, please place the frame on a FLAT SURFACE (this is crucial).

    • All the components are cut or drilled by machine for highest precision, but with uneven tightening, it is possible to warp the frame.

    • Using your hand, try to wiggle with the frame sides and check, whether some corners are lifting up or not.

    • In case you find some imperfections, release the screws, press the extrusions against the FLAT SURFACE and tighten them again.

    Im having a problem with step 10. Place it on glass surface and there is about 0.5mm gap uneven between the 2 legs (if you look at 1st the image, leg at the long extrusion nearest from you and the leg at the short extrusion furthest from you). Spent one hours unscrew and screw everything back. but as long as Im tightening the screws, the gap is there. Loosen the screws a bit and the gap show up again…. tried all different ways from swapt left right turn the extrusions around still have the same gap at the same location. Have been google, watched youtube, check forums… seems like not only me but many struggling with this… Hopes you guys should given clearer guidance…eg… if not better design then should there are any tolerance….Spent over 4 hours screw and unscrew without any success

    Bill D - Reply

    any success ? Same problem here. I think maybe one of my extrusions is not copped straight (off by a hair).

    Tim -

    Same problem… Even on Tom's live build (https://toms3d.org/2018/01/16/building-t...) he has this issue.

    Alexis Ramel -

    I had similar problems. It’s really tricky to get it perfect. As soon as you tighten the last screw, things are out of whack again. Also, there are surprisingly many surfaces in the house which are NOT actually as flat as you think. Not even all glass.

    If you want to know whether a surface is flat, do the wiggle test and then turn the printer 90 degrees, then repeat the wiggle test. If it wiggles more or less after turning then you know that the surface isn’t flat. No point in using that surface since you will not get a straight frame.

    In the end I approved a 0.5mm wiggle and we will see if it smoothens out in the auto calibration .

    Jos - Reply

    I have the same problem. Unfortunately, after loosening and re-tightening the screws about five times (and even turning around some extrusions to see if that might help), I now have a stripped screw (please, please, switch to Torx, Prusa). I’m actually now worse off than I was at the beginning, with more wiggle than initially, but I’m afraid to retry, since I don’t want to strip more screws… I’ll just have to hope it’s good enough.

    Lukas - Reply

    Tried this on 3 printers using a perfectly flat surface.

    There is always a wobble from the front right to the back left. All 3 printers do this.

    When screws are loose there is no wobble

    Only way I could fix is to expand the screw holes from 5mm to 5.5mm using a drill

    Tom - Reply

    For clarity, wich screw holes do you mean? The ones in the center frame or the ones in the front and back plates? Haven’t ordered a printer yet, but I want to make sure I know what I’m getting myself into ;-)

    Koen -

    Front- right to back-left wobbling here also. Normally the front right corner is up in the air. Loosened and retightened all screws multiple times in different order, the result is always the same.

    Attila - Reply

    Well, after spending more hours than I wanted, trying to figure out what was happening, I had help from support and ended up identifying the problem. Not solving it yet, but identifying it. Remove all extrusions and put them laying on the flat table, check if they rock (rotate them on all 4 sides), if so, you have a bent extrusion. If they don't, move on to the next test, put them standing up on the flat surface, check if they rock, there was one of mine that was rocking a lot while vertical. Smooth sanding with a 1200 grit sand paper revealed a small imperfection, something like a burr on the top of the long extrusion. I was happy at this point, reassembled everything, still out of geometry. Last, I did the rock check with the front plate and it is really bent. They are providing a replacement. Prusa support is awesome.

    Giacomo - Reply

    Also, one thing that helped me very much was having the frame supported by two woodblocks ( be sure the blocks are the same height ) underneath the extrusions, so I could check if the problem was there before attaching the front plate or not. And that way I could see that it was pretty spot on without the plate and once I tightened just a tiny bit of the plate bolts it would twist the assembly, thus identifying the defective part. I hope it helps you guys out. It was frustrating.

    Giacomo -

    My problem was similar. The front plate was slightly warped and pulled things out a bit so that the right front was just a fraction high. I fixed this by blocking the left front extrusion up and stressing the frame while tightening. This ended up perfect.

    James A vonBehren -

    My problem was similar. The front plate was slightly warped and caused the right front to be slightly high when everything was tight. I loosened all the screws on the front plate, blocked the left front extrusion high, and stressed the frame while tightening all the screws - alternating left and right and following the diagonal procedure for each extrusion. That worked perfectly and didn’t generate any issues in Calibration during startup.

    James A vonBehren -

    Since this step is so tricky, I’d recommend modifying the previous instructions to advise against tightening at all. Just take the screws up until flush. Then tighten all of them on a glass surface at this step. I could not get mine perfectly square on a glass table either. I hope a little wobble is OK, if I have to, I’ll just stick a piece of masking tape under a leg.

    Ryan Sealy - Reply

    I agree, tightening should happen at the end. I had the same problem and had to tighten/loosen all of the screws repeatedly.

    Chip Brown -

    Hello, yes I recommend tightening the screws just to be flush, not all the way.

    Martin L. - Customer Support -

    Since this step is so tricky, I’d recommend you modify the steps above to not tighten the screws at all. Just make them flush and tighten them all at this step. I couldn’t get mine perfectly square either. I hope a little wiggle is OK. I’ll use a piece of masking tape if I have to.

    Ryan Sealy - Reply

    I too have had this problem. As soon as the final screws were tightened the frame would then wobble with a 1mm gap.

    After much swapping around and many, many tries, I found that reversing the front plate cured the problem. Almost suggesting that either this or the the rear plate were not completely flat but, without a surface plate, I cannot confirm that.

    Anyway maybe his will help someone else. Wasted 4 hours on this step.

    Neale Brodie - Reply

    I too had this problem and no matter what I loosened and tightened I always ended up with a 1mm gap on one diagonal. I checked the extrusions for squareness and the frames for flatness but couldn’t make sense.

    In the frustration of many assemblies and dissassemblies, I eventually found by reversing the front plate the problem dissappeared. The plate looked perfectly flat but it wouldn’t take much more than the slightest twist to cause the problem.

    Hope thsi helps

    Neale Brodie - Reply

    Same issue as everyone else (front right, rear left diagonal wobble). Tried reversing front and rear plates and flipping a few of the rails… no luck. No matter what I try, I can’t get rid of the wobble (no obvious defects on front or rear plate when checking for rocking). Engaging support.

    D Wellnitz - Reply

    Same with me, any luck?

    Tim -

    I had this problem too, rocking front right-back left. After slacking off, and re-tightening a number of times without removing the wobble completely, I found this process to work,

    Loosen all screw and make just finger tight. Place the smallest Allen key under the front left, clamp ( with gentle pressure!) the back left. Apply a weight to the front right. Tighten all screws as previously described. Result =no wobble.

    Paul - Reply

    Paul! I cannot thank you enough! Your solution worked perfect for me. Well done sir!!

    simon.assender@gmail.com -

    You just saved me from my obsession of getting things perfectly square! The allen wrench trick worked on the first try to fix that 0.3mm wobble that was driving me nuts. Just enough to make noise when it wobbled.

    …and I just realized that I forgot the power supply nuts…

    Chris Lindberg -

    +1 to this.

    After a long time trying I read Paul’s trick. Thanks a lot! Works in one try for me!

    Awil -

    Freaking. Brilliant.

    After an hour of fighting this, I used your trick and it worked the first time :)

    Joe Bourrie -

    Just encountered the same issue; about 0.2 mm wobble from front-right to back-left (measured with feeler gauge). Tried your technique and it eliminated the wobble! I think it’s important to mention for others, as another poster did, that very few surfaces are perfectly flat so even if you get perfect stability on one surface, it might be wobbly on another. Luckily for me, I had Chuck Norris finish the top of my workbench so it’s pretty much atomically flat. Thanks Chuck! (oh, and thanks to Paul too, I guess).

    Maximus McNobblybits -

    Thanks Paul, this worked well for me. Following your steps, I actually over corrected the wobble a bit, so then it wobbled front right to back left. Applying continuous pressure against a flat surface, I loosened screws and re-tightened, one junction at a time, until the wobble disappeared. Great tip!

    Matthew B -

    Worked a little too well. Wobble moved to opposite corners. LOL.. But, only had to loosen and redo the front screws while holding down extrusions. Thank you for your suggestion Paul !

    jimlester21@gmail.com -

    Bingo! Thank you for this solution.

    Dewi Eirig Jones -

    Same problem here. Tried several times to loosen screws and retighten, but could not completely remove the wobble. Tried this and found it to work.

    Loosen all screws and make finger tight. Place the smallest Allen key under the front left. Clamp (with gentle pressure!) the rear left to your work bench. Place a weight on the front right. Tighten screws as previously described. Result - no wobble.

    Paul - Reply

    Hey that technique worked out fantastic. thank u

    matthew -

    +1 to this. It sounds like some wobble is withing tolerances, but this got mine perfectly solid.

    Cosmo Jones -

    Brilliant advice, Paul!

    Quick questions with “Loosen all screw…” Do you mean all 32 screws? All *outer* 16 screws? Just the right outer 4 screws? or…?


    Gene Dahilig -

    For the record, I too am having wobble with the front right, rear left. Paul’s advice looks promising. And I will also try reversing the front plate to see if that helps.

    Prusa: You may not be able change the order of your comments, but you can post more info in the text for this step that clearly state what is expected (i.e. tolerances: “most of the time the wobbling won't affect the print“) and include more tips on how to correct a wobbly printer.

    I also have to give this step just 2 stars. Comments, however, get 4 starts.

    Gene Dahilig -

    +1 , Paul your way to resolve it is excellent; I was fighting with the frame for 2 days; my frame was exchanged by Prusa support as well but that didn’t help and after all I got quite angry… Your way to resolve the issue is the only one working; thanks again…

    Jacek Olszewski -

    Worked for me too!

    Marcin -

    PAUL SAVED THE DAY! I was having the exact same issue. Using Paul’s trick I was able to get it level enough that I won’t worry about it anymore.

    Mike -

    +1 for Paul’s technique. This step goes a lot easier if you upgrade to torx screws. One US source is albanycountyfasteners.com.

    Jim Lombardo -

    Thanks, Paul. I unsuccessfully spent 2 hours trying to get the geometry level. Finally, in frustration, I checked the online manual here and tried your method out. I put the smallest Allen key under the side opposite to which was too high. I then put a 10kg dumbbell weight on the frame and tightened everything up again. No wobble at all now. Thanks again!

    Eric Mathison -

    After an hour of fighting this, your trick worked perfectly :)

    Joe Bourrie -

    This worked great for me as well. Thanks! It’s surprising how non-flat everything in your house is…

    Jonno Schmidt -

    GENIUS. Ive built 2 mk3s now and this has worked so bloody well.

    patryk -

    Thank you paul! This worked for me! very easy!

    Maike Köhler -

    Thank you Paul! this worked for me! i love you! xD

    Maike Köhler -

    Thank you Paul! this worked for me! i love you! xD

    Maike Köhler -

    +1 to @frostie (Paul’s) approach. It probably varies printer to printer, but I started with the smallest allen key and found that was enough to reduce, but not remove the wobble. I ended up working my way up to the second largest allen key along with a 35lbs weight. There is still a _very_ slight wobble, but it’s down to .1mm or less (less than a sheet of paper) from ~1mm or more.

    D Wellnitz - Reply

    I am having the same problem. I’ve tried Pauls approach and that has removed some of the rocking, from about 8 sheets of paper to now 4 but its quite a lot still!

    Alistair - Reply

    Hi Alistair, in case you can't reach straight frame without significant movements, please contact our support at info@prusa3d.com.

    Jakub Dolezal -

    And where is Prusa's support ???

    Joaquin Villar - Reply

    Hi Joaquin, depends on your needs. If you have a problem with the instructions I'm here. In case of faulty parts, please contact our support info@prusa3d.com or by live chat on our eshop.

    Jakub Dolezal -

    Also had the same problem. wobbled around 2-3 pages.

    Did as Paul describe above with the smallest allen key and used clamps with a light pressure to hold left back and front right down on the aluminium extrusions worked perfectly no wobble at all . thanks for the tip Paul

    Mattias - Reply

    I had the same problem and used Paul’s trick to get the wobble down now to only about 2 pages of paper on a Flattish surface.

    It would be extremely helpful to know specifically:

    What is the tolerance of this and to what extent will calibration correct for this? Shall I continue building now that I have only 2 pages of wobble or should I invest another 4 hours into getting it perfect. Frankly, on a glass top surface at home when I rotate 90 degrees the wobble goes away (indicating to me that even the flattest surface in my house isn’t actually 100% flat.

    Andreas Sjolund - Reply

    10mn step, become 1h30 step….1 star…Thanks Paul ;-)

    Jeremy - Reply

    I experienced the same issue as everyone else (rocking from near right to far left).

    I’ll try some of the suggestions here, and contact Support if necessary. But meanwhile, it would be extremely helpful if the instructions could give the following information:

    — What does “tighten the screws fully” mean? Obviously most of us building the printer are not using torque wrenches, but if there is any way to describe in words the degree of tightness that is desirable, it would be a big help. Could overtorquing cause some of the issues experienced?

    — How flat does it need to be? Is there a way to describe this in words — sheets of paper, or a certain fraction of a millimeter, or whatever? In the real world, nothing is perfectly flat. I clamped my YZ frame (with screws loosened) to a surface plate (a very flat piece of granite) and tightened the screws very carefully, but I still get a small gap (fraction of a millimeter). Can this be compensated for later during calibration?

    Frank - Reply

    Hi Frank,

    to answer your questions:

    What does “tighten the screws fully” mean? Fully tighten means to tighten until you feel reasonable resistance against your hand, you need to achieve full contact between both parts, but on the other hand, use reasonable force as you can easily damage/crack some part of the printer. Best practice is to tighten the screw gently for the first time, check it the parts are still moving and then tighten again to achieve full contact. In case of the YZ frame, I advise being cautious as you might warp the extrusions.


    Jakub Dolezal -

    How flat does it need to be? I already asked my colleagues to test this. We are cutting all parts using on CNC to achieve the highest precision, so I'm sure most of the time the wobbling won't affect the print (and yes completely straight frame is almost impossible to achieve in the real world). Also, the printer is able to compensate for the certain level of uneven surface geometry. For now, please try to achieve as flat frame geometry as possible and then move on with the assembly process. This shouldn't take more than 10-20 minutes. Only in case you see the difference of several millimetres, please contact our support (info@prusa3d.com).

    Jakub Dolezal -


    I think these responses from PRUSA should be posted at the top of the comments listings as they seem to indicate the prevalent rear left/front right wobble is common and that a slight wobble (I’ve got mine down to 5 sheets of paper at front right) will not affect the final printing and can be taken up within the normal bed levelling.

    Phil Higgins - Reply

    Hi Phil, unfortunately I can’t change the order of the comments. Anyway, based on your feedback the instructions are continuously updated and there should be no need to read the comments. Regarding the frame geometry our developers need more time to check the influence on the print quality.

    Jakub Dolezal -

    For the record, I used Pauls trick in kind a lazy way by simply holding down the side while tightening and got it down to 2 pages of wobble. During setup my frame came out as perfectly square so there you go. I’d caution people against trying to deform the frame to get it perfect.

    Andreas Sjolund - Reply

    Definitely do not deform anything! Follow the instructions or contact our support to get the frame straight.

    Jakub Dolezal -


    I suggest simply check the lower plane with 2 thin threads, each going from corner to corner. At the point of crossing you will see what the deviation is. Mine was close to zero.

    Marijus Petraitis - Reply

    This is horrible. Spent so much time trying to fix this slight front right wobble and its still not fixed. Should be in the step instructions the this little bit is ok.

    phr0ze - Reply

    What an absolute waste of life!

    I have never seen something as frustrating as this, and I built the MK2s.

    What is going on Mr. Prusa? There is a front right to rear left wobble. The only possible thing it can be is the large frame piece is not true.

    With all of the people experiencing the same issue, your team must have come across the same issues during the build process. Please provide the workaround that they are using.

    David - Reply

    i too have this exact wobble after 2 weeks back and forth PRUSA said that this wobble is ok and the xyz calibration will correct for this now I find there is a known issue with the firmware mesh bed leveling is not working due to PINDA firmware issue which make it impossible get a good first layer

    Art - Reply

    +1 for Paul’s technique. Worked for me first try.

    Blaine Collins - Reply

    I had a minor misalignment, but loosening and retightening all screws of back and front plate that hold the extrusions, while keeping the extrusions pressed against a granite flate surface, fixed it.

    Etienne van Ballegooijen - Reply

    +1 for Paul’s advice. I had to try different allen keys but I noticed that it amount of wobble changed immediately. I finally got it to level out.

    Still, like one of the commenters above, it all assumes that your reference level is actually level. I got different wobbles on different places (4 places on a granite counter, 1 on a glass table). So YMMV, no matter what. I finally had to pick one spot and go from there.

    Good luck, all!

    Gene Dahilig - Reply

    A mirror will give most perfect flat surface to test against.

    Ron Peno -

    I had the problem initially, but after holding down the end plates with some weights, and tightening the screws gradually I was able to get a rock steady frame, only took a few goes and now it’s fine.. I had to loosen the rail screws too, but along with the rubber feet any small rock will be taken up by them.

    Martin Wright - Reply

    I have also spent hours trying to get my frame to keep from rocking. I see the same direction as described above so it must be a SYSTEMATIC error in the design or fabrication of parts. I have confirmed that that my extrusions are straight and flat to the main frame because they don’t rock when blocked up on pieces of extra extrusion. The rocking only starts when the end plates are tightened to the frame.

    What is the “BEST” solution so far? And what is the “ACCEPTABLE” tolerance for the high corner (in mm please)? I am using a billiard table (pool table) to check flatness.

    Timothy W. Skloss, Ph.D. - Reply

    So I did all this AFTER I had torqued everything down to 40 in-lbs. I guess I should read ahead or maybe you guys should put a note to do the final torque at the end after you check alignment. Maybe not. I was off by about 2mm on one corner. I tried to loosen screws till the one corner came down and then re tightened them. So now 1-2mm off in one corner. So then I loosened all the screws. It lay flat. Tightened them while holding the frame down. it worked… so then I torqued the screws and it put me back to about 1mm off in one corner. I will try “Pauls” method next. As per Prusa’s comment here I am probably good to go with the frame as it is now…. but !&&*…. what fun is it if you can’t get it closer to perfect…. right?

    One question. Lets say it is 2mm off in one corner. And then when I put it in my enclosure I would usually shim under any feet to make them all solid. So for that case, Would the quality of prints be worse because of that corner being off?

    Bob Keenan - Reply

    OK…. did the Paul Method and it worked!

    Bob Keenan - Reply

    I’ve used the Paul method as well after much fighting with the wobbling. However, I’ve run into an interesting situation. I’ve managed to remove the wobble while on my build surface, but when moved to the location where the printer will sit, it has the same wobble in the front right corner. After that, I made adjustments again based on the final location of where I plan to keep the printer. Now if I move the printer back to my build table, it has a wobble at the front left. When I use a level and straight edge, I’ve not able to see any real difference between the two surfaces that could explain what I’m seeing. Obviously, it makes sense to have the printer setup as flat as possible. However, short of having confirmation about which surface is the most flat, would it make sense to set it up based on final location?

    TrinityEllis - Reply

    I, too, spent quite a bit of time chasing wobbles. Like some others, I am building on a sheet of glass; and I am surprised that some here are seeing .5mm gaps, because my wobble was no where near that great.

    What worked for me was loosen all 32 screws, then, applying weight to the frame, just snug first the inner 16 screws, and then the outer 16. Then, apply the final tightening, again first to the inner 16, then the outer 16.

    Stephen Gomes - Reply

    I used a similar method to Stephen to remove a slight wobble. Loosened screws, rested my arm corner to corner across the high bit and then tightened down screws, though not quite as tight as I had originally gorilla’d them. Repeated across the other corner to corner. +1 for building on a piece of glass if you have it.

    Darin White -

    Wobble problem here… Always the same corner, with the PRUSA logo towards you, the nearest corner on the right. After a lot of assemblies the best I can get is 0.15mm (measured with thickness gauges). Weird thing, the other 3 corners are flat. Flatness checked on a Marble rectified surface, same wobble when turned 180°

    jorgemarmo - Reply

    +1 to @frostie (Paul) method…

    after a 1st pass I got a 0.05mm wobble on the other corner (PRUSA towards you, the closest on the left) and I said “that’s good enough and my thumb’s blister is killing me” then I just checked all screws and slightly “over-tightened” the ones holding the long extruded profile on the right) and no wobble at all!

    jorgemarmo - Reply

    Mine fit perfectely from the very beginning. No wobbeling at all.

    Erwin Meisel - Reply

    Same problem. Paul’s method works (thanks Paul!) but I had to repeat it three times, unscrewing and rescrewing a different location each time. Josef - something’s wrong here and we need a better fix than twisting things to make it flat. Since we all have the same issue on the same corners, I would suggest that there is something wrong with the frame itself?

    Phil - Reply

    Thanks, we will check it out.


    Tomáš -

    Same problem also, in the same corner.

    Will try Paul’s method tonight, hoping it works.

    John Pope - Reply

    Hi there John, thank you for the comment. We will check it out.


    Tomáš -

    Same problem with my kit. There is always a wobble from the front right to the back left (about 1mm). I used a torque tool to ensure the same torque on all screws…

    It would be nice if Prusa could provide us with a maximum deviation (in millimeters) that it is acceptable. I didn’t saw Paul’s method and proceeded with the assembly, and now I kinda don’t know if I should go back and try to correct the problem or if 1mm is acceptable…

    Paulo Carmo - Reply

    Yes, Prusa should either confirm if it's not a problem or fix it if it is.

    Alexis Ramel -

    Easiest way: First, tighten extrusions except the front left, then tighten the rest 8 screws on front left by turn, increase the torque evenly, NOT in diagonal. You will find this way is easy to control.

    Hsiung - Reply

    Making the frame perfectly level is a really difficult (and frustrating process). You end out having 1-2 mm difference between two legs in diagonal. Frustrating !

    Need improvement !

    Gilles - Reply

    This part is VERY frustrating. However, I have done the following 3 times now on 3 different Prusa’s and this seems to work. The issue each time was the side with long extrusions would not level. Either the left side or right side looking at the frame from the long extrusions facing you. The fix at least for me was to do the following. I used a piece of thick glass that I confirmed is indeed flat. I loosely screw the long extrusions to the main frame and front frame - screw heads barely touch frame. At this point everything should be perfectly flat. Before I tighten I use clamps to clamp the front frame and main frame. Once clamped, I tighten the front right side but just barely. Then I tighten the left backside the same. Then the back right side and then the left front side. Then repeat again in a diagonal pattern for the screws and the location until they are all hand tight. DO NOT OVER TORQUE any one screw. When you are done, release the clamps. Everything should be perfect. It works for me.

    Enzo Maini - Reply

    After getting to this step mine had a slight wobble. What seemed to work was first loosening the front and rear plates. I then let the rear plate hang off the work bench with the frame sitting flat. I did this to let gravity level the two sides. I then did the same with the front plate. It was slightly out of square. I found that three of the bars were level. There was only one, when I pressed on it, caused it to wobble. I then loosened the screws holding that one bar to the frame and repeated the process of tightening the screws with that bar hanging off the workbench. This process removed my wobble. In this case gravity was my friend.

    Ben Vizzier - Reply

    Read through all of the other comments on this so I knew this was going to be a potential issue when I started assembling my new printer tonight. I took a micrometer to the frame at various points and was able to verify what others have already reported. But unlike some of the more extreme measures that have been suggested, I think I have found an easier and more workable solution.

    When looking at the front (long) extrusion piece on the right I noticed a slight skewing. I removed all 8 bolts, rotated the extrusion 90 degrees (so the face that was on top is now on the side), reinserted the bolts and tightened. No more wobble.

    The second thing I found that can make a difference was by rotating the front and/or rear plates, as the alignment of the holes on either side may not be exactly symmetrical.

    Michael Jones - Reply

    Like others above, at first assembly I got 0.55 mm of wobble.

    I put the frame on a surface plate with the front extrusions pointing up and using a machinist’s square noted that the right long extrusion was tipped back (upwards after final assembly) ~0.35 mm over the ~150 mm span. The left long rail was tipped a bit the other way. I checked the squareness of the extrusion end fastened to the frame, and it was way better than the 0.35 mm. Sounds like a problem in the frame, or the paint on the frame.

    The paint plus paint varied in thickness by about .08 mm in the area where the extrusion was attached, which might explain part of the error. For the paint to be the culprit, it would have to be asymmetrical, which it well might be, depending on the spraying pattern.

    Anodize would be much better for precision.

    Check the frame flatness pre-paint—the one or two mm wobble in the comments above is not likely caused by paint.

    I applied Paul’s method, got wobble less than .05 mm, and decided it was time to move on.

    Gordon Stout - Reply

    I had the same problem, but here is what worked for me:

    1. Release ALL the screws, securing frame and plates to the extrusions, so 32 pcs.

    2. Use a plank to deliver even pressure on both extrusions while securing them.

    3. Do not overtight the screws, 90 degrees after you feel a counterstand will be just fine for all the screws.

    4. Tighten the screws to the plates, THEN then to the frame.

    I’ve overcome this problem using the steps above, hope that will help.

    Sorry for my bad english

    Ivan Sadetsky - Reply

    I also found like Ivan that tightening the screws to the plates and then to the frame was what helped my situation. I put a little bit of preload under the front left corner (a credit card about 0.8mm thick) and then just used my arms to keep the four corners on the ground as I slowly tightened the screws in turn. It would be nice if they could sort out an engineered solution for this. Can you imagine counting up all the hours (and aggravation) people fussed with this? I’m also going to read all of the comments for a section first before jumping into it as I had to undo everything. I’m eating all the gummy bears now.

    Rich Rector - Reply

    This is simply ridiculous…84 people troubled to comment on here with the same Prusa defect issue, likely many more quiet folks. Yes, Paul is the man, but it moved my rock to the other side, and each time I mess with this my screws become more damaged. And I even bought a torque wrench feeling pride to do this right, what a disaster. And Prusa is mostly silent on here, my first experience with this brand is not a good one so far, very disappointed!

    Scott - Reply

    Paul’s comment is better than sliced bread, and it helped me a lot, but just be careful cause in my case the smallest allen key was too big and I ended up having it wobble the other way round. So best is to first measure the distance of the gap you have with sheets of paper, and then use the same number of papers instead of the allen key. In my case a credit card was perfect.

    Werner Marais - Reply

    Tip: This needs 2 people. We loosened all rear and front plate screws slightly. One person holds down with equal pressure the front and back extrusions and other person diagonally tightens the screws! Worked perfectly and we checked with a spirit level and not wobbling. Took 10 minutes.

    Shayne - Reply

    Having built many object that require them to be square and true, I kept all of the screws loose in steps 2 thru 10, and then only at the end tightened things up. I did this on a flat surface, and applied pressure to the extrusions with my hand, so that everything remained square. After final check and calibration, I was spot on, so take your time and do this right.

    Matt Laudato - Reply

    is the main upright to touch the work surface or just the front and rear plates

    John Firman - Reply

    No wobble on mine. I’ve checked on 3 different surfaces. I made sure to tighten all of the screws evenly (with a torque wrench) and checked each extruded aluminum piece to make sure it was square after tightening. Maybe Prusa corrected the issue?

    Eddy Gleason - Reply

    Hi Eddy,

    All components are undergo a quality control before they are shipped. In case of faulty parts, please contact our support info@prusa3d.com or by live chat on our eshop.

    Official Prusa Support

    Martini Horaki -

    • Note this step is optional for now. We recommend mounting the feet to protect the surface on your table (workbench). However, you need to lift the frame up before each turn.

    • There will be extra step at the end of the assembly to remind you of the antivibration feet.

    • Antivibration feet (4x)

    • Turn the YZ frame on the side and insert the antivibration foot inclined, then rotate the foot until you squish the rim inside the extrusion.

    • Repeat this process on all 4 feet. Place them 2-3 cm from the end of each extrusion.

    I found that using hot melt glue holds the feet well. I saw on several you tube videos that they came off a lot during the build.

    James Zimmerman - Reply

    I used hot melt glue on the feet and it holds well. I saw on several You Tube videos they came off during the build a lot.

    James Zimmerman - Reply

    Hi James, the feet come off only if you try to turn the printer without lifting it up first. The friction between the table and each foot is simply to big.

    Jakub Dolezal -

    My experience after using the printer for a month: The feet come off constantly unless you pick it up from the frame and rise it perfectly vertically (which just isn't ergonomic if you have it on a table (or especially a high table like I do). As for me, I’ve vowed to hot glue them the very next time it happens!

    Andreas Sjolund - Reply

    My frame is perfectly square as on step 10 the Geometry check proved, however, when I put feet on… now it wobbles… Is that okay?

    Jeff - Reply

    Hey Jeff,

    The feet are from the rubber - it will wobble a bit, but won’t affect the print.

    Official Prusa Support

    Filip Misiło -

    • ATTENTION: Starting 01/2018 Y-holder-front and Y-holder-back parts are replaced by Y-rod-holder, which has the same shape for all 4 pieces. Please see the second picture. Nut insertion and tightening procedure remains the same.

    • For the following steps, please prepare:

    • Y-holder-front (2x)

    • Y-holder-back (2x)

    • M3x10 screw (8x)

    • M3nS nut (8x)

    So is the new “Y-rod-holder” the same part as the old “Y-holder-front”? I could not find the “Y-rod-holder” part on GitHub.

    Christoph Stahl - Reply

    Hi Christoph, I think there were some extra tweaks to the design, I urged the developer to upload it asap.

    Jakub Dolezal -

    Appear the designs for front and back were merged, add foot protruding from back design to the front and it looks like you have it.

    Harry Townsend - Reply

    • Take the Y-holder-front and insert M3nS nuts.

    • Make sure you've pressed the nuts all the way in.

    • In case you can't press the nuts in, don't use excessive force. First, check if there isn't any obstacle in the nut trap.

    • Ensure and adjust the alignment of each nut with the 2mm Allen key.

    • Repeat this step for the remaining Y-holders. At the end, you should have two pairs, front and back.

    Take the scewdriver to push it in

    Muck - Reply

    I find the problem is not so much that they won’t fit but that they are a touch loose, so they fall out when it comes time to rotate later.

    Florence Chan - Reply

    I had the same problem but ended up with two assemblies with ‘tight' nuts. Use those for the front plate where you have to do the rotation. On the rear plate you can hold the loose nuts in from below as there is nothing blocking access.

    I would have tried wedging a small sliver of paper between the nut and the 3D part (without obstructing nut threads) if I had more nuts that didn't lock in.

    I think the part could be improved by incorporating a small lip or bump to hold the nut in (slightly inwardly bowed cutouts may work as well).

    Kris Boyle -

    I concur on Kris Boyle’s suggestion above. I used the assemblies with the secure nuts on the front, the two assemblies with a loose nut I used on the back. My tip is a strip of blue painters tape applied to the bottom kept the nuts in and oriented and allowed me to secure the nuts without flipping the whole frame. The blue painter’s tape can easily be removed without issue, even if you need it for all four assemblies.

    JBFLA - Reply

    One of my Y-holders’ nut traps came with a little piece of plastic protruding off the wall and now I an unable to fit in the nut. Any idea how I can fix this? Should I could try cutting it off?

    Zerg620 - Reply

    I cut at the extra plastic with a 9mm OLFA blade and a push pin and managed to cut away enough plastic to fit in the last nut. I would not recommend the blade if you can help it since I did accidentally cut the wall of the Y-holder.

    Zerg620 - Reply

    Hi there Zerg,

    thank you for your comment. I will see what I can do about it for future assemblies.


    Tomáš -

    For the procedure, checking alignment with a screw rather than the Allen key also checks that the threads are clear. This might help prevent cross-threading later.

    For the block, it might be good to have a small hole to allow pressing out a miss-placed nut with the small Allen wrench in case that becomes necessary.

    Gordon Stout - Reply

    • First, take the Y-holder-front parts and place them on the longer extrusions, openings for screws must be facing up.

    • Rotate the 3D printed parts towards the front plate.

    • Secure each front holder with two M3x10 screws. Tighten both screws equally, but not completely. We will tighten them fully later on.

    • Second, take the Y-holder-back parts and secure them with M3x10 screws on the rear plate (with shorter extrusions). Tighten both screws equally, but not completely. We will tighten them fully later on.

    For me the Y-Holders do not fit on top of the long extrusions. I seem to have the “new” version where all 4 are the same. I had to sand the bottom down in order to reach the screws.

    Peter - Reply

    I just received my Kit yesterday and I seem to have the new pieces. They all fit fine for me. Sorry Peter!

    Andreas Sjolund - Reply

    Yup they worked for me also.

    Donnell - Reply

    I had a problem where not all the nuts would stay inside the 3D printed “Y-holder-front” and the “Y-holder-back” parts when flipping them over to install per the instructions.  The best way I found, (for me anyway) was to rotate the printer frame upside down, (180 degrees) and install them with the nuts facing up.  Just make sure that you have the side with the nuts facing the outside of the printer when screwing them in.

    Joseph Rigdon - Reply

    I used this trick, worked like a charm. Thanks :)

    Tor Andre -

    Good idea. I did it right side up and used a small allen wrench to dab some glue inside the Y-Holder.

    Zaki Ullah -

    Same as JosephR, I had one nut persistently falling out. The only solution indeed was to turn the complete frame upside down, then it became easy. I believe it would be good to mention this neat “trick” in the documentation (which by the way so far is excellent). I also have 4 Y-Holders, they all look the same - no problems there this far…

    Alan Rusyak - Reply

    Superb manual so far : well done Prusa-the best assembly manual I have ever seen and love the continuous improvement of capturing comments. We had 4 identical orange pieces but the nuts / screws wouldn’t quite line up. Not obvious whether it was a tolerance in the FDM orange parts or the CNC metal plate (position of holes)-the solution involved tipping the printer in various orientations (inc. completely inverted) to make the nuts drop into different positions within the orange pieces when trying to get the bolts to bite, for each of the second holes, as the first one would screw in easily. With jiggling and care they all worked within a few minutes however.

    Jonathan Histed - Reply

    Hi Jonathan, thanks for the comment. Printed parts are checked before shipping and the same goes to the metal plate. Tolerances are accounted for, so it should fit without any significant adjustments.

    Jakub Dolezal -

    Regarding torque for the bolts on printed parts, I have found to just snug the part against the frame, then turn slightly more makes it perfect.

    Scott Story - Reply

    Same as Joseph R, Alan R, and Jonathan H - some nuts would slip out of alignment. Turning the unit upside down kept the alignment so I could get the screws to attach. Please either document this fix or cut the nut slot in the holders just a trifle smaller for a snugger fit.

    Brian hughes - Reply

    +1, would revise the step for the short extrusions to include flipping the frame upside down, works great.

    Nate P -

    I also had the issue with the nuts falling out, and ended up flipping the whole frame over. I realized though that this could have been avoided by attaching these parts before attaching the front/back plates to the frame. Is there a reason they are done after? It might be worth changing that around in future versions of the manual.

    Mister Glass - Reply

    There is a suggestion at the previous step regarding loose nuts. I used blue painters tape on the bottom of the assembly to secure the nuts in place long enough to get the screw started, it is easily removed and non-permanent.

    JBFLA - Reply

    The holes for the screws in the 3D printer parts were every so slightly undersized or imperfect. I found it very helpful to first run screws into the 3D part with the nuts installed without going through the printer frame before trying to instal them in place.

    Connor M OLeary - Reply

    I have a problem at this part. 2 nuts rotate freely in the Y-holders, with the screw stuck in. I can’t get the screw in, and unfortunately I can’t get it out either.

    I would hold the nuts with pliers, but in the Y-holders it’s almost impossible. =/

    Antoine Van Vooren - Reply

    Too late to edit… Here’s a video showing my problem: https://photos.app.goo.gl/oVzGWP2XDPXqmW...

    Antoine Van Vooren -

    • For the following steps, please prepare:

    • Y-belt-idler (1x)

    • M3x18 screw (1x)

    • M3x10 screw (2x)

    • M3nN nyloc nut (3x)

    • 623h bearing housing (1x)

    For me the bearing has markings 623Z (really tiny text on the bearing).

    Kari Söderholm - Reply

    Hi Kari, yes the bearing inside is 623z, but it is enclosed in a housing, that is why it is named 623h.

    Jakub Dolezal -

    It would be clearer if the "M3 nyloc nut" label matched the “M3nN" label on the parts bag.

    Gabe Yoder - Reply

    Hi Gabe, thank you for the suggestion, I will update the description ;)

    Jakub Dolezal -

    $@$* happens. I manage to get a M3x10 screw stuck on the M3 nylon nut on the Y-belt idler. It happens when I try to screw it in while not noticing that the M3 nylon nut is not install straight in the Y-belt idler. I have to cut the Y-belt idler plastic to remove the stuck screw and nut. (Caused by the screw thread damage). Replaced the screw and nuts and install it carefully on the broken screw hole side of Y-belt idler.

    Ben Mah - Reply

    Where can I get the stl to reprint this Y-belt Idler?

    Ben Mah - Reply

    Look for the Original Prusa i3 MK3 stl pack here, recommend print setting are written on the same page: https://www.prusa3d.com/prusa-i3-printab...

    Jakub Dolezal -

    Thank you very much.

    Ben Mah -

    Thank you very much.

    Ben Mah -

    Hello: I too had issues with the Y-belt idler M3nN nyloc. I find the 10mm M3 screws just too short. In order to insure that the idler is loose enough to tension the belt later, if the M3nN sockets aren’t clean you can easily not have any play with the 10mm screws, or they won’t even engage with the base thickness of the idler part and the cross plate. I actually replaced the 10mm screw with one slightly longer and that worked better to tension the belt. I would suggest reviewing the tolerances and maybe increase the screw lengths to 12mm on the idler only (or even 15mm). 15mm may be a bit too long, but there is plenty of clearance. (Regards, Mark Deley) Otherwise - well written, and nice assembly instructions, and the Haribo’s are great!

    Mark Deley - Reply

    My second Prusa build, first MK3 and yet I still managed to strip my Y-belt-idler by being too aggressive in tightening down the nut. I already know better and these very instructions told me: “Be careful not to break the idler during tightening. “ Bummer. Of course, my Mk2S is in parts so I had to order a replacement. So my question is: I received a “we’re on back-order” update for the replacement. Any ideas as to how long? The new frame is way sturdier than the 2S. I’m pleased with you guys, displeased with myself! This is why we build though: to learn.

    Twerd - Reply

    Hi Twerd, replacements should be shipping fast. In case you have a friend around with 3D printer, he can print this part for you. Look for the Original Prusa i3 MK3 stl pack here, recommend print setting are written on the same page: https://www.prusa3d.com/prusa-i3-printab...

    Jakub Dolezal -

    And thus began the struggle. Getting the nylock bolt seated cleanly in the recess so that the bolt would thread took a LOT of clean up of the plastic parts. This continued with pretty much every close mating of plastic and metal in the following steps as well. I found that two things alleviated this:

    1. Careful cleanup of the plastic part with X-acto and micro file.

    2. 'Firm' dry fit of all plastic to metal part assemblies prior to using them in the assembly step. This ensures that nuts are properly seated perpendicular to the bolt and firmly seated in any recess. This will vastly improve the chance of catching the thread without cross threading you do the actual assembly.

    Kris Boyle - Reply

    • Take the Y-belt-idler and insert two M3nN nyloc nuts from the top. The rubber inside nuts must be facing up.

    • Turn the idler to the other side and insert the last M3nN nyloc nut. The rubber inside the nut must be facing towards you.

    • Make sure all three nuts are all the way in.

    • In case you can't press the nuts in, don't use excessive force. Take M3 screw thread it from the opposite side of the printed part, as you tighten the screw, it will pull the nut in. Be careful not to break the idler during tightening.

    I’d suggest modifying this step to make it clear that the nyloc nuts should be pushed as far into the idler as possible; without them at full depth, the bolts installed in step 18 don’t have enough range to make a useful tension adjustment once you get to step 36.

    Kenneth Albanowski - Reply

    Hi Kenneth,

    Thanks for the suggestions, I have a general update regarding the nut insertion in mind.

    Jakub Dolezal -

    @jakoob are you still “thinking about it”? because this issue is still actual, and it’s 12. of August 2018.

    patrick.fehr@fbc.ch -

    Hi Patrick, there is a note regarding using the screw to get the nut in. I've recently updated the description clarifying the nuts must be all the way in.

    Jakub Dolezal -

    i used another similar bolt to help pull in it (probably should’ve had a washer, but didn’t tighten it down)

    Jonathan - Reply

    I found the blunt end of an unsharpened pencil to be pretty handy. It let me push with an even pressure to seat the nuts flush.

    Rueben Nilsson - Reply

    Thank you! I’d been trying to get them flush for a while - this was the trick.

    Neal Cronkite -

    I also found this tip really helpful! My fingers are too big to manage the nut otherwise!

    Zerg620 -

    Its not irrelevant which hole one puts the nyloc for the idler. Maybe make this clearer in the description.

    Its shown correct in the photo, but one have to look carefully to see if not familiar with this kind of assembly.

    Possibly easier to see it the part is orange (mine is black).

    Olav - Reply

    As mentioned by Kenneth the nuts have to put in fully. My first attempt ended nearly in desaster: the screw with the nut turned and turned, no way to unscrew. So a metal saw was needed to remove the screw. Next attempt: I used a long screw from the spare bag and when the nut was inserted fully, removed the screw and replaced it by the right one.

    The desaster was avoided and the situation healthy, as from this time I did it every time this way!

    Wolfgang Peters - Reply

    I overdid the the advice for using a screw to pull the nut into place, resulting in the nut spinning in the part. Had to use a dremel to cut it off and try again, ruining the hole in the process. Next time, I’ll screw in the first couple threads of a longer screw and pull the nuts into place. This will be my first PETG printed part, because the lower nut is temporarily replaced by a zip tie.

    Joshua - Reply

    We had problems getting the nuts to drift home. We used Maun parallel sided (smooth) pliers to drift them home (that move with the faces being parallel- a somewhat specialist tool but worked well), but one nut tipped over slightly and refused to go all the way home. a couple of taps with a tack hammer, with the component sitting on a flat surface drifted it home. (which is essentially a very narrow nosed hammer, a draper expert 19724 used by upholsteres for tacks)

    Jonathan Histed - Reply

    Similar to Jonathan, I used plain old channel lock pliers (small sized) that fit fine down in the channel and pressed evenly across the nut. Worked well.

    Darin White -

    I found a picture hanger with a nail hole the screw wouldn’t slip through, I then flattened the hanger with a set of pliers. Next, I stacked a small washer (too big for the screw) against the back side of the plastic hole, the flattened hanger, then pushed the screw through. Now, thread the nut onto the screw and tighten into place.

    Mark Tellier - Reply

    This may be the moment for some ADVICE for fastening the delicate printed parts.  They can break or split when using too much force.

    Hold the SHORT end of the allen key with your fingers.  (Not the long end as it produces too much torque.)  Stop turning when it starts to hurt.  In most case this will be the moment of correct torque.

    Klaas - Reply

    My nut holes were too small and had to whittle away with a knife to get screws to meet nuts.

    Kevin Whitaker - Reply

    These holes might be a little bit tighter so that the nut holds in there nicely :).

    Tomáš - Reply

    At the end of this page, you’ll need those nuts inside the part since the screws are small, so using the screws to tighten that nut into the part I’d highly recommend, just don’t get too crazy and tighten it so tight that you break the part in half.

    Zerg620 - Reply

    Yep, you should be quite carefully with these. However, if you do not apply extensive force you will not break the part :)

    Tomáš -

    Good practice with Niloc nuts says that they should not be reused. the nylon’s locking action is reduced each time a fastener is done and undone so a suggestion is made that this is kept in mind referring to future work on the frame for things like maintenance. blue Locktite can be used if this ever becomes a problem in the future.

    Mustrum Ridcully - Reply

    m3x18 should be longer… you can’t use it to pull in the nut, and based on comments it’s very important to seat that nut firmly. a longer screw would solve both issues

    Robert Eden - Reply

    For many cases where nuts needed to be pushed in, I used my parrot jaw pliers, with several layers of masking tape applied to the jaws. It gives even pressure, and the tape minimizes the damage to the plastic. In some cases, I also used a wooden dowel and a ball peen hammer to gently tap the nuts in. Used the ‘pull through with screw’ technique as a last resort, which worked well.

    Matt Laudato - Reply

    After using a mini electric drill to clean some excessive plastics in the hole carefully for several times, I can (finally…) push the nuts in with moderate force.

    getabyte1432@gmail.com - Reply

    Using the screw to fasten the top but is not a great idea. In my case the screw got stuck. Had to cut it off with a dremel to get it out. And even then I couldn't separate the two with 2 tongs and wd40. Luckily there are spare parts you can use if it happens.

    shibe - Reply

    My approach to seating the Nyloc nuts is to use kit spare pieces to construct a "nut-puller-inner".

    Insert the Nyloc nuts into the idler housing hex cavities. At this point there is no need to seat the nuts full depth.

    Thread an M3n hex nut onto an M3x30 screw (spare parts) so that approximately 10mm of the M3 screw thread protrudes through the nut. Using just your fingers, screw the protruding threads into the Nyloc nut from the idler housing's backside. You are threading into the side of the nut which does not have the Nyloc locking ring.....DO NOT thread the screw beyond the point where it just touches the Nyloc locking ring.

    Now use needle nose pliers/5.5mm wrench to turn the M3n nut in the direction that moves it toward the Nyloc nut. As you continue turning the nut, the M3n nut/M3x30 screw combination will act as a "nut-puller-inner" and will easily seat the Nyloc nut.

    Turn the M3n nut in the opposite direction to loosen the puller and remove the M3x30 screw/ M3n nut.


    John McDaniel - Reply

    • Insert the prepared bearing in the Y-belt-idler.

    • Bearing housing orientation doesn't matter.

    • Secure the bearing with the M3x18 screw. Don't fully tighten the screw.

    • Place your finger on the bearing and ensure it can rotate freely. If needed adjust the screw.

    The bolt could stand to be a bit longer. Mine just barely engages the nylock insert. I added a bit of blue Loctite to play it safe.

    Scott - Reply

    Hi Scott, please check there is nothing blocking the bolt. I've assembled several MK3 printers and it was always about some small pieces of PETG left in the hole.

    Jakub Dolezal -

    18mm is OK for me

    Petr Navrátil -

    Agreed. I swapped the 18mm length M3 screw with a 20mm.

    18mm is just too short, and 20 is the perfect length.

    Patrick Crawford - Reply

    Hi Patrick, 18 mm should be enough, please see my comment to Scott (above yours).

    Jakub Dolezal -

    I agree with Patrick and Scott. The bolt is a bit too short. It doesn’t properly touch the nylock inset and there is nothing blocking the holes.

    Guntor H - Reply

    Hi Guntor, thanks for the feedback, the 18mm screw should be enough, but I will check it with my colleagues, who are assembling printers.

    Jakub Dolezal -

    If you assemble the screw nut and just the block first to pull the nut fully into the hex in the block then 18mm is more than enough to work as described.. problem is that the nut is a good/tight fit in the hole and needs some help initially.

    Martin Wright -

    18mm is enough here for me!

    Christoph Stahl - Reply

    It worked perfectly for me with 18mm screw!

    Christoph Stahl - Reply

    18 was fine for me, but you need to make sure the nuts are seated all the way down as far as they can go. This turned out to be a bit tricky. In once instance I used a screwdrivers to push the nut in. In another case I used another screw to pull it into place (which is suggested actually in a previous instruction).

    Andreas Sjolund - Reply

    After making sure no plastic was blocking the nut or the head of the bolt, I tightened the bolt until it was tighter than it needed to be, the bearing wouldn’t move at all, and the threads where just peaking through the end of the nut. I then backed the bolt off until the bearing housing spun freely. The bolt is just to the end of the nut. Fits perfectly.

    Daniel Horn - Reply

    Your method/suggestion worked to give me a perfect as well.  Look for extra plastic in the holes then over tighten just a bit to pull everything in nice and snug and finally loosen just enough got get it to spin freely.  Thanks!! :)

    Joseph Rigdon -

    Good suggestion, this should be mentioned in the manual.

    Travis Howard -

    Did the same thing (and really tightened it, so I’m sure the nut won’t go anyu deeper). The nut is flush with the plastic but the screw is only halfway through the nut. So I’d use a 20mm as well. Perhaps I could clean the plastic somehow, but it just seems easier to use a slightly longer screw.

    Tako Schotanus -

    18mm was perfect. installed bearing then read the comments and adjusted as needed.

    allan arthur - Reply

    Opened the comments here because I had the same thought. OK, got the 18mm in fine, just barely in the plastic part of the nut. But I think there is enough space for another 2 mm. Just to play it safe.

    Quentin - Reply

    Hi there, I just finalized the Y-belt idler: My proposal would be to use a M3x20 screw (as posted by others as well). I needed some tricks to do it with 18mm screw, but doing it with 20mm would be far easier, and there is enough place in the idler for 20mm as well.

    Leo - Reply

    Hi Leo, thanks for the suggestion. For the MK3 kit we aimed for the lowest variety of the screws, but I will ask designers to have a look at this printed part once more.

    Jakub Dolezal -

    It seems the hole on mine wasn’t printed well and the bolt won’t go in the hole and thus can’t reach the screw and reach the bolt. I tried carving it to make it bigger. Would a 20 mm be ok to use? does the kit provide it in the spares?

    Brian - Reply

    so after 30 more mins of carving it went in. and 18 works fine now

    Brian - Reply

    Hi Brian, I'm glad it worked for you. The printed parts are checked, but in case you still have some issues with them, please contact our support for a replacement.

    Jakub Dolezal -

    Same here, the traps for the nylock nuts are really tight. But with a little force it’s viable. The bolts length seems fine for me.

    Mathias Ehret - Reply

    We used Maun parallel pliers to get the nut flush with the surface so the 18mm screw engaged with the nut, (as the nut didn’t want to go in easily deeply enough for the screw to engage), and screwing it in whilst the wheel was still fee to rotate, it went only to the metal of the nut, but not to the nylon. We continued to tighten the screw till the wheel stopped rotating, then backed off, the nut had sunk further into the orange housing by now, so the loosened assembly works : the wheel rotates freely, and the screw bottoms out at the end of the nut, fully engaging in the nylon of the nylock, but with no excess.

    Jonathan Histed - Reply

    I managed to break this component, be careful with the tightening on the top bolt its layer thin towards the top. I know what i will be printing first!

    Also agree, longer bolts here would help pull the nuts in to place.

    Iain Monteath - Reply

    For me it was the nut hole too tight to push nut deep enough so the bolt could engage. After trying to clean the hole with the flat screwdriver I’ve decided to push the nut in using another nut as a pusher, putting this other nut on the table and carefully pressing the idler with nut inside from above, trying not to break the part. The nut went deep enough to the hole so the bolt could engage.

    Alex - Reply

    Using adjustable pliers to squish the M3nN nyloc nut seemed to work.

    Erin Baker - Reply

    Recommend manual update: If you have trouble seating the idler-bearing nyloc nut, use a M3x25 from the spare bag to pull the nyloc nut in, then replace it with the M3x18. It is best to install the bearing while doing this, to help prevent breaking the plastic part.

    Andrew E. Mileski - Reply

    Hi Andrew, good point, using a longer screw is a solution, when you can't press the nut it. Thanks for the suggestion ;)

    Jakub Dolezal -

    M3x18 and M3x10 fit.

    to fit M3x10: use M3x18 and the frame to pull the nyloc nut in with the bolt,

    to fit M3x18: usa M3x25 and some material to put between walls of belt-idler (so it does not break while pulling in the nyloc nut) , then pull the nyloc nut with the bolt.

    Marcin - Reply

    The M3x18 screw barely meets the Nylock nut. The nut being Nylock seems pointless since getting that far info the nut would lock the bearing. I’m going to go buy some M3x20’s tomorrow, so the Nylock nut is meaningful.

    Steven Hodgen - Reply

    I think what would be helpful here, is a printed temporary block to use in place of the bearing that you can use to tighten in the Nylock nut with a M3x25 without worrying about damaging the idler . Seems that the trick on all of these nuts is that they need to be pulled into place with a screw.

    Mark Mealman - Reply

    I found that the hex hole was a bit too snug for the nut to sit deep enough for the 18mm bolt to reach. There was no stray PETG in the hole so I took a needle file and gently filed the sides of the hex test fitting the nut until I got it to sit further into the hole so the 18mm bolt could reach. Looks like the sides of the hex hole weren’t completely flat, but rather convex. Slight filing down allowed the nut to slide in while still being snug.

    Patrick Ryan - Reply

    See my comment in Step 16 for the basic concept of a "nut-puller-inner". For the Step 17 Y-belt idler Nyloc nut the procedure is just a bit different.

    With the M3n nut removed from the M3x30 screw , insert the M3x30 screw through the idler housing from the side opposite the idler bearing's Nyloc nut.

    Push the M3x30 screw through just far enough to allow you to thread the M3n nut onto the M3x30 screw. Turn the M3x30 screw/M3n nut until about 10mm of M3 screw thread protrudes through the nut.

    As in my Step 16 comment, use just your fingers to thread the M3x30 screw thread protrusion into the Nyloc nut. DO NOT thread the screw into the Nyloc locking ring.

    Now use needle nose pliers/5.5mm wrench to turn the M3n nut in the direction that moves it toward the Nyloc nut. As you continue turning the nut, the M3n nut/M3x30 screw combination will act as a "nut-puller-inner" and will easily seat the Nyloc nut.

    Turn the M3n nut in the opposite direction to loosen the puller and remove the M3x30 screw/ M3n nut.


    John McDaniel - Reply

    • Rotate the frame with longer extrusions towards you.

    • Take the Y-belt-idler and place it on the front plate. Note there is a mark (circle) on the printed part facing up.

    • Secure the Y-belt-idler with two M3x10 screws.

    • DON'T TIGHTEN the screws fully, you will need a "loose" Y-belt-idler to adjust the tension in the belt later on.

    I’m not really sure what the red circle with the X in the last picture is suppose to mean but it makes it seem like the circle facing up is wrong. Maybe just putting a arrow pointing at the circle on the part would be better.

    Paul Betz - Reply

    Hi Paul, the red circle is connected with red text in the description. I've made adjustments to the picture. It is it understandable now? Point is, you shouldn't tighten the screws fully as you need them to adjust the position of the idler later on.

    Jakub Dolezal -

    Yeah last pic makes no sense!!

    Alex Tutusaus - Reply

    Hi Alex, picture adjusted. Please let me know, if it is understandable now. Thanks

    Jakub Dolezal -

    Sorry I was a bit confused also by the last picture. Here are some suggestions which may make it more clear.

    1. Maybe add some rotation lines to the pic indicating that you are discussing the tightening.

    2. Make sure the red color in the picture is the same color as the red text that goes along with it. In this case the colors seem to be slightly off so I didn’t associate the arrow with the text at all.

    3. If possible, reserve the color red for really important information and use a different color for the steps.

    Andreas Sjolund - Reply

    Hi Andreas, thanks for the feedback. I will think about different approach as there are certain limits with current software behind this manual. For example the red colour is predefined, no chance to change it. Usage of red colour in this step is on purpose, it is crucial to have the idler free, so you can adjust the tension of the belt later on.

    Jakub Dolezal -

    I think the main problem is that the image shows what shouldn’t be done, and there is no matching “do this instead” image. My suggestion is to add one more image, showing the idler with the screws loose (like the first image, but zoomed in exactly like the second image), and then change the second image to just have the entire idler crossed over by red lines?

    Zaz - Reply

    Hi Zaz, thanks for suggestion. I have this step on my list already and your idea is almost the same as mine ;)

    Jakub Dolezal -

    I found the 10mm screws to be too short to engage the nylon locking washers in the nylock nuts. So I substituted 18mm screws from the Spares bag. (Proper use of Nylock nuts means you thread the screw in through the metal side first, then engage the nylon washer as the screw emerges from the other side.)

    Jay Sinnett - Reply

    Seeing other comments from above, only issue I have had is the nylock nuts don’t fit in the hex hole free enough to reach the 10mm screws, but have also noted that if pushed into the hex quite hard they are far enough in to be used with 10mm screws…

    Martin Wright - Reply

    Before fitting the block to the frame add the nuts, and then screw them into place with the nuts fitted, when the 10mm bolts are tightened up they pull the nuts hard into the hex in the block, this in turn makes it easy to fit the block after this process…

    Martin Wright -

    Suggestion for better instruction: Fully tighten the screws until the nuts are well seated in their pockets and the idler assembly is firmly attached to the plate. Then loosen each screw three full turns. This gap is required for installing the belt later in this section.

    Timothy W. Skloss, Ph.D. - Reply

    i couldn’t secure the idler with the m3x10 screws ,so i used the m3x18…

    khong - Reply

    I had to do some (very) gentle tapping with a light hammer to get the nuts in and straight. You won’t be able to use the 10mm screws if the nuts are not perfectly flat and well seated.

    Phil - Reply

    NOTE: Make sure your part, nut, screw, and frame CAN be tightened for the next to last step. If your nut doesn’t go in properly, like mine didn’t, try screwing the nut in tightly then leaving the part, nut, and screw together for a minute or two. My screw wouldn’t even reach the nut and this is what I did to fix it.

    Zerg620 - Reply

    Hi. The M3x10’s do not meet the Nylock nuts here. I’ve made sure they are seated well, as deeply as they will go and appear the same as the photo. I tried putting the screw in by itself, just barely meeting the threads, then held it against the frame, so I could see if how close to possible it was, and it’s definitely not going to make it. Others have used M3x18’s, in the spare bag. I’m going to go buy some M3x12’s tomorrow.

    The funny thing is the instructions say to leave the part slack, for tightening later on, but there is no way to even get the screw in the threads. If the screw were an 11mm long it would make it to the threads, but still not to the lock.

    So far, the frame of this printer is much nicer that the one in my MK2S, and I love Prusa, but you guys need to make sure your screws are long enough. I shouldn’t have to go buy screws to get a clean install. :-)

    Steven Hodgen - Reply


    The Front plate and the y -idler holes didnt match up. there about 2 mm difference in height.

    Gonna try to drill a new hole for it

    Hole drilled, its not perfect but atleast it fits. just need to put a little perssure to tighten them

    De Roeck Benny - Reply

    Make sure you are putting the idler on the front side of the printer, so on the long aluminum extrusions

    Jeff -

    Like others who have commented, I tried all the suggestions but was unable to allow enough slack for tensioning with the 10mm screws. I found some 16mm screws (same diameter and thread) and they seem to have fixed the problem Interestingly I found them in the spares for an 3D printer kit I built about 5 years ago.

    David Day - Reply

    What worked best for me here, and in all similar scenarios where the nuts don’t seat well, is to simply use a little bit longer screws and get the nut to catch onto the screw thread when it’s still outside its seat. Then it will pull the nut into the seat. Of course you must probably clean the seat hole a little bit from 3D printing residue of all sorts, and in cases where the screw length may be in the way you simply need to clear the nut seat all the way.

    Another tip is to always drill your screw holes out beforehand with the correct drill bit size (3mm for M3 screw of course…), beacuse you don’t want then to thread through the printed part, unless that’s the purpose in special cases where nuts are not possible. It can crack the print and if you have two holes from two parts only one can be threaded, trying to join 2 threaded holes will cause tension and strip one of the hole threads or crack the part.

    I would suggest that the stl’s for all nut seats be adjusted with a fraction of a millimeter.

    Werner Marais - Reply

    • For the following steps, please prepare:

    • Y-axis motor (1x)

    • Y-motor-holder (1x)

    • M3x10 screw (4x)

    • M3n nut (2x)

    • Ensure you are using the correct motor, there is a label on the bottom of the casing. The reason is, each motor has different cable length.

    The M3X10 screws which went into the motor were fractionally too long and they hit the motor before tightening the plastic part.

    I had to grind off 1mm on each.

    Hans Heck - Reply

    Hi there Hans, might have been imperfect plastic part :/ I will keep an eye on this one. Thank you for you feedback.


    Tomáš -

    I think it would be worth a call out here that these are NOT the nyloc nuts. I wasn’t paying close enough attention and use the wrong nuts. I discovered on a later step I had the wrong number of nuts left and and to backtrack to figure out where they went. Fortunately it wasn’t too difficult to push the incorrect nuts out and switch to the correct ones.

    John Petrangelo - Reply

    Me too, but easy enough to fix.

    Bill McKay - Reply

    • Take the Y-motor-holder and insert two M3n nuts.

    • In case you can't press the nuts in, don't use excessive force. Use an M3 screw from the other side and tighten it.

    • Place the Y-motor-holder on the motor, ensure the correct orientation as in the picture.

    • Using two M3x10 screws tighten holder and motor together.

    I think that the motor mount is a high vibration point why aren’t we using m3nN M3 nyloc nut instead of the m3n nuts it would make more sens,we are installing the m3nN nuts on the y axis idler holder but not on the motor mount . is there a reason ?

    Marc Dumoulin - Reply

    Hi Marc, thanks for the suggestion. I will talk to the devs.

    Jakub Dolezal -

    @jakoob have you talked to the developers yet? This question is still open and it’s 12. August 2018.

    patrick.fehr@fbc.ch -

    Hi Patrick, I've talked to them. Slotted openings are in general more complicated for printing than holes for hexagonal nuts. That is why we use the slot for M3nS only if they are necessary.

    Jakub Dolezal -

    How tight should we go with a torque wrench?

    James Smith - Reply

    Hi James, I don't have values for tightening the printed parts yet, but we are working on it. Use reasonable force as you can break them. I recommend tightening using Allen key for now.

    Jakub Dolezal -

    I used the paper guide for this step and used lock nuts because of it, after having to use those exclusively for a couple of steps I didn’t notice the change. They fit just fine and I could not get them out again. I agree with Marc that this is probably better. Used two of the spare lock nuts for the linear bearings.

    Pascal Scheffers - Reply

    He’s not joking about breaking them. Just snapped the bolt off inside the motor. Here’s hoping rotating the motor 90° won’t be an issue because I CAN’T get it out.

    Mike Brookfield - Reply

    exactly the same happened to me..broken nut inside

    Andrea Bruna -

    I didn't notice the change in type of nuts in this step and accidentally used M3nN nuts instead of M3n. Need to use the spare for the later step. But above comments said that this might be better.

    Siu Chuen Chan - Reply

    When moving to “home” (min-Y), a bearing acts as an end-stop, striking the rear smooth rod holder.

    This is not healthy for the bearing, plus can easily move it out of position despite the U-bolt, which can be a problem mid-print after a Power-Panic.

    The motor mount can easily be modified to prevent this from happening. Instead, the belt holder and motor mount take the impact.

    Issue #76: Y-Axis Crash Detection Inconsistancies

    Andrew E. Mileski - Reply

    Dear Prusa team,

    Could you confirm it is not a problem to use lock nuts for the Y motor holder?

    I did the same mistake as few others people and used lock nuts instead of normal one.

    Currently I cannot remove the nylon nuts from the holes maybe with just high force but It is to risky…

    What do you think?

    Thank you!



    János Barta - Reply

    The lock nuts will not ‘lock’ if the screws don’t protrude into the locking element. If you want lock nuts, you will need M3x12 screws. I cut down a couple of the spare M3x18 screws to m3x12, but this not a good solution for the kit: if the longer screws were accidentally put in the motor hold-down position they would bottom out and cause problems. Best fix for the kit: deepen the recesses, use M3x10 with M3nN nyloc nuts.

    I put a couple of 0.4 mm thick washers under the motor mount to shim the motor away from the plate, which it was otherwise hitting. This allowed the motor shaft to be more perpendicular to the plate, which should improve belt alignment. I’ll leave a note in a later comment section if I come to regret this!

    Gordon Stout - Reply

    good practice would specify Nilock nuts for the holder to frame use where vibration might be a problem. Did the Developers say why the changed to regular m3 hex nuts here? I used blue loctite here as I would on any vibration prone fastening not using any other anti vibration system(nylock)

    Mustrum Ridcully - Reply

    I used an M3x10 screw and threaded the M3n on the end about a quarter way through the nut. Then, I used the screw to manually place the nut into position, wiggle it down gently, and then backed off the screw out of the nut. This was better than tweezers or trying to fight the nut to go flat and into position.

    Phil Norris - Reply

    • Take the Y-motor-holder and place it on the rear plate (short extrusions).

    • Ensure correct orientation, the motor shaft must be facing towards PSU holders.

    • Secure Y-motor-holder with two screws M3x10.

    The motor mount breaks easily, so be careful!

    Jørgen Stokke - Reply

    How does it break? Crushed by the screws? Layers break apart?

    Guido Kimble -

    Mine cracked along the layers while tightening the top screw. It seems to still be solid enough, so I’m hoping to be able to print a replacement once the printer is up and running.

    Harold Toler -

    If the screw did not easily slip through the hole in the printer back plate, and if the screw had to cut a thread through the plastic part, then I would suspect it’s because of the 2 threaded holes being joined. There can always only be 1 threaded hole, and where nuts are used then just a smooth tight fit (but not threaded) for the screw is best. The 2 threads can strip or break something.

    Werner Marais -

    Prusa, you are an awesome and progressive company, so please stop torturing us with 10mm screws and nut seats. 10mm is too short when going through the metal frame and the nut seats are almost never completely clean in a real world. In many many cases, like this one a screw length of 12mm can make the worlds difference. Otherwise thanks for the awesome work and bravery in always pushing the limits!

    Werner Marais -

    Should the motor wires come out the bottom?

    John Tucker - Reply

    Hi John the motor wires should be facing down, while the Y-axis motor is mounted.

    Jakub Dolezal -

    I was careful with tightening the screws evenly, used the long arm of the wrench with one finger. Got things real tight, no problems with the mount so far.

    Todd Scott Anderson - Reply

    There is some small amount of play in the motor mount.

    Since my work-surface was level, I placed a spirit-level on the central frame to ensure it was level (no rubber feet), then moved the spirit-level to the motor and ensured the motor was level while I tightened it to the frame.

    I suspect I’m over-tightening everything, but haven’t had any breaks nor failures yet. Will be printing back-up parts ASAP in case something splits or breaks.

    Andrew E. Mileski - Reply

    here i couldn’t secure the motor with the m3x10 screws again so i used the longer m3x18 screws..

    khong - Reply

    I used M3 Nyloc nuts and M3x12 screws to attached the mount to the frame. Perfect fit. Seems a better choice for a motor mount. Stay with the M3x10 screws for the stepper, as depth stop is important there.

    michael_farady - Reply

    The upper nut-holding 3d printed part was not holding the nut, it’s now broken and freely turns, when the screw is turned. No way to get it out again…

    patrick.fehr@fbc.ch - Reply

    After mounting, the motor isn't completely close to rear plate, which cause the shaft isn't parallel and drag the belt moving. I recommend the angle between two mounting face of motor holder should over 90 degree in order to make the motor stay close to rear plate.

    Hsiung - Reply

    Hi there,

    the motor must be fully tightened. Try to re-do the step 20 and make sure to properly insert the nuts into the plastic part.


    Tomáš - Reply

    This is a three person job. One person reading instructions, one person doing QC, and one person doing assembly. If it were not for the blue box highlighting our missing PSUs….we would have proceeded without them. Oh well, guess we will have another Cream Ale.

    Del Norte - Reply

    Using the M3X10 did not work at all. We took two spare M3x16 from the spares packet and cut them down to 12mm - worked perfectly, would recommend 12mm if you them as a better option.

    Shayne - Reply

    Had a hard time with the M3x10. Eventually got it to mounted after driving the M3n nut much further in the fitting then what’s shown in the pic above. This is done by screwing it tight by itself without the frame. Once the nut is drove further in, unscrew, mount, and screw it back with the frame in place.

    Ben Tang - Reply

    • For the following steps, please prepare:

    • Y-carriage (1x)

    • Y-belt-holder (1x)

    • U-bolt (3x)

    • Linear bearing (3x)

    • M3nN nyloc nut (6x)

    • M3x10 screw (2x)

    • For MK2/S owners, the Y-carriage is now symmetrical in one direction, therefore the dot (countersink, marker) orientation for bearing insertion doesn't matter.

    I think you should add 2. Y-axis assembly Step 14 Correct bearing orientation from the Original Prusa i3 MK2S kit assembly v2.05 instructions.

    Waldemar - Reply

    Hi Waldemar, thanks for the suggestion. I will confirm this with devs and make adjustment if necessary.

    Jakub Dolezal -

    Missing 2 Nyloc nuts. Opened spares.

    David Wilbanks - Reply

    Might want to specify the screws are M3x10.

    Bruce Moore - Reply

    Bruce, thanks for noticing. Description updated.

    Jakub Dolezal -

    few balls (3-4) fell of the bag when unpacking one bearing. Still slides on the rail when I tested. Using it anyways.

    Juraj Mr. - Reply

    Hi Juraj, 4 balls are quite a lot. I suggest to get a new one and replace it soon. Missing balls might cause increased friction leading to issues during prints.

    Jakub Dolezal -

    It might be nice to state that the dimple on the plate needs to be facing up/down. I installed the plate upside down and had to reverse it later when the holes did not line up with the heat plates.

    Keith Manley - Reply

    Hi Keith, the Y-carriage is symmetrical, so it doesn't matter on which side you install the bearings. You just need to have correct orientation of the “side” with two bearings, while assembling the Y-carriage on the Y-axis.

    Jakub Dolezal -

    Is the dimple meant to be at the bottom when installing the plate?

    Ed Jimenez - Reply

    Hi Ed, no it doesn't matter, see my comment to Keith Manley and also follow the instructions in the manual, where is stated, the orientation doesn't matter.

    Jakub Dolezal -

    The middle hole is slightly assymetrical (off by 1.2mm) so I cannot manage to assemble all screws and have to leave out the middle one. Flipped frame at the beginning might have allowed me to install the middle screw now. Please add a note to check if heatbed and frame match in the very early assembly state even if they are supposed to be symmetric.

    Do Not Print - Reply

    Jakub, you had replied above that the instruction manual states that orientation doesn’t matter. However, the manual specifically says it doesn’t matter for the MK2/S printers. I have the MK3 printer. Should the manual be updated if orientation doesn’t matter for other printers?

    Jennifer Krull - Reply

    Ah, I think I understand, now, that you were letting those with the MK2/S printers know that the orientation no longer matters.

    Jennifer Krull -

    Missing 1x M3x10 nut (sourced spare from spares bag)

    Alex Champion de Crespigny - Reply

    Missing 2 Nyloc nuts. Instead 2 normal M3 nuts. Opened spares, too.

    nikolaus.brandtner@gmail.com - Reply

    I’m also had to raid the spare parts bag for two nylon nuts.

    Richard Murray - Reply

    Thank you for your feedback. We will check it out :)


    Tomáš - Reply

    Hi you need 8 M3nN nyloc nut for this step Six for the U-bolt and 2 for the Y-belt-holder. I used two from spare

    Johannes Löbel - Reply

    Sorry I made a mistake, you need only six nut but still are two niloc nut missing

    Johannes Löbel - Reply

    • When placing bearings onto the Y-carriage, make sure that they are oriented as shown in the picture. One of the tracks (row of balls) has to be in line with the cutout for the bearing!

    • This orientation has to be followed in all 3 bearings on the Y-carriage!

    It would be helpful to explain what is meant with ‘orientation’ in this case. First time builders like me only discover what is meant here when assembling the X-Axis step 3 as that step contains a drawing of this bearing. I thinnk it would be beneficial to have that drawing inserted here too.

    Jeroen - Reply

    It would be helpful to know what is meant by “track”.

    JC Wren - Reply

    Looking ahead to X-axis step 3 as suggested by @jeroen helped me figure this out, I think. Notice that in the picture there are rows of ball bearings inside, that are facing straight down. I am thinking we will want to mount one with the ball bearings straight down and one with them rotate 45 degrees?

    Graham McIntyre -

    Jeroen (@jeroen), JC Wren (@jcwren) and Graham (@grahamm78) by the track is meant row of balls inside the bearing casing, step description was updated. For the Y-axis please use same rotation for all the bearings, do not turn them 45°.

    Jakub Dolezal - Reply

    If you look closely inside the bearing you will see the row of tiny balls is not straight all the way to the ends. At the ends the row of balls bends slightly making it look like a broad grin. I “think” what this instruction is telling us it that the grin all needs to be in the same direction on all 3 bearings when they are mounted on the Y Carriage. Is this correct?

    Andreas Sjolund - Reply

    Hi Andreas, yes you’re right. The balls on the edges are slightly off the line, but don't try to adjust them. Point of this step is to have one row of balls (most of it) positioned above the smooth rod, this is valid for all three bearings.

    Jakub Dolezal -

    I was looking for your comment Andreas and I believe Jakub missed your point. The ‘grin’ orientation should not be important. If it were, these bearings would have a directional orientation to adhere to as well. Jakub reinforced the point that the line of bearings should be inline with the cutout.

    I tried to get the grin to be oriented in all the same direction, just in case, but one of the bearings on the double side has failed that inspection. I don’t believe it’s a problem though.

    Todd Scott Anderson -

    Thank you, Jakub! I didn’t notice before, but when I look inside the bearings, there’s little tips that make a U, grin, or smile shape. Now it all makes sense to make sure that all the smiles face the same way!

    Zerg620 -

    One of the tracks (row of balls) has to be in line with the cutout for the bearing!

    I am assuming that this means that then placing the bearings on the cutout, be sure to keep a row of balls inside the bearing on the bottom (6 O Clock) so that they are on the same horizontal plane as the top of the cutout?

    tim - Reply

    Hi Tim, yes one line must be on 6, as in the picture. Because as soon as you install the Y-carriage on the printer, this line of balls will be gliding on the top of the smooth rod.

    Jakub Dolezal -

    The bearings don’t glide easily on the tracks. They sound like metal rubbing against metal and catch a little. All three bearings do this. I noticed this before I tightened up the U-bolts

    rickard - Reply

    Hi Rickard, if the movement isn't smooth from the very beginning, please contact our support team. Contact info is in the first chapter of this manual.

    Jakub Dolezal -

    May I suggest that these bearing be lined up at a 45° angle against the rods, instead of 90°. This so that there is more bearing surface area supporting the Y axis carriage. I have done this on my machine and the difference has been night and day. My Y axis is significantly quieter and smoother. The scratching sound is almost completely gone and the movement feels more slick.

    Sandy Loyd - Reply

    Hi Sandy, your suggestion is always welcomed :) We've tested several positions of the bearings on multiple printers, but I will forward your direction to the devs.

    Jakub Dolezal -

    I concur with Sandy. The forces on the smooth rods are similar to those on a beam—tension on the bottom, and compression on top. Orienting the bearings as recommended/shown puts the bulk of forces exerted on the rod on two rows of balls (top & bottom), while leaving the other two rows of balls “neutral”.

    Rotating the bearings 45° distributes both tension and compression forces across two rows of balls each.

    Rufus Clupea - Reply

    It would be nice if the bearings were pre marked with a line on the outside of the barrel. I used a permanent marker to do mine. That way you can tell if they get shifted later on.

    William - Reply

    Hi there, thank you for the tip. Yet I am afraid that something like that is not possible :/


    Tomáš -

    Should Bearings, touch one side, and live on the other side a gap - that is what illustration shows. Or should they be in the middle.

    Jan Negrey - Reply

    Seems like the intent is that that of the 4 rows of bearings, 2 should be vertical (up and down) and 2 should be horizontal when it’s finished, this way the load is completely on one set of bearings. (It seems counter-intuitive that it’s not placed at 45 degrees and lands on two races of bearings but I assume the dev guys know what they’re doing).

    Also it may feel/sound a bit “scratchy” when you slide the bed back and forth but if you press down on it just a bit and slide it a few times it seems to get smooth.

    Ybl84f1 - Reply

    • This is VERY IMPORTANT part of the assembly, which can significantly influence printer's behaviour. PLEASE read following lines carefully!

    • Place the Y-carriage on a flat surface. Orientation doesn't matter.

    • Insert linear bearing in the cutout and secure it by U-bolt.

    • Hold thumb on the U-bolt and turn the carriage. Place nyloc nuts on both ends of the U-bolt.

    • Start tightening the nuts, BUT ENSURE you are tightening both nuts equally and AS SOON AS EACH NUT REACHES THE SURFACE OF THE Y-CARRIAGE STOP TIGHTENING!!! We will finish tightening the nuts in the next step.

    • Repeat these steps for the remaining two linear bearings.

    • Over tightening nuts leads to deformation of the bearing and all the issues connected with it. Please follow the instructions.

    The MK2 assembly instruction tells to align the bearings in a special position.


    Step 14

    doesn‘t matter anymore?

    Heiko Schultz - Reply

    Hi Heiko, you can use the “special position”, it will be added to this manual shortly.

    Jakub Dolezal -

    Does the countersunck marker facing down no longer matter? I see in the pictures from the next step you have it facing down, so I am doing that. (Since you say orientation does not matter, I suppose that is explicit, but since the the holes in the middle of the carriage are asymmetric left/right, it is confusing. I’m assuming those holes are no longer used.

    Paul Meyer - Reply

    Hi Paul, looks like you've missed our information at step 22: “For MK2/s owners, the Y-carriage is now symmetrical in one direction, therefore the dot (countersink, marker) orientation for bearing insertion doesn't matter.”

    Jakub Dolezal -

    The bearings don’t glide easily on the tracks. They sound like metal rubbing against metal and catch a little. All three bearings do this. I noticed this before I tightened up the U-bolts. Is this normal?

    Ken Ondo - Reply

    Hi Ken, try again step 30 and let me know ;)

    Jakub Dolezal -

    I used a 7/32 racheting (72 tooth) socket wrench, tightening a quarter turn until they touched the surface, looked at the arch, and made sure it was even. Then I double checked that the bearing is exactly in the center before another quarter turn to tighten the bearing down. Also… I think the IGUS part RJZM-02-08 is a worthy upgrade. :)

    Mr Cookie - Reply

    It would be nice to add that the nuts will be tightened further later.

    “AS SOON AS YOU REACH THE SURFACE STOP TIGHTENING!!! They will be torqued to final tightness later.”

    Guido Kimble - Reply

    Hi Guido, good point! Description updated ;)

    Jakub Dolezal -

    Hello, the tread on one of my brackets is too thick. I can’t get a nut over it or put it through the holes. Please ship me a replacement!

    Pieter Jan - Reply

    Hi Pieter,

    please contact our support with your contact details, my colleagues will help you. Use either mail (info@prusa3d.com) or livechat on shop.prusa3d.com Thanks

    Jakub Dolezal -

    My U brackets were either the wrong size or bent. They did not fit well into their holes and marred their threads while being inserted.

    Evan - Reply

    Hi Evan, please contact our support at info@prusa3d.com, in case you can't fit them in and apply nuts properly we will send you new ones.

    Jakub Dolezal -

    Should the bearing have some play to it to ensure one doesn’t over tighten or does the bearing still need to be tightened securely to the cutout? I am a bit confused by


    due to the use of “you”. Does you mean the bearing, the nut, me the operator? I apologize for being nit picky, I’m just honestly confused. :)

    tim - Reply

    Hi Tim, it is about the nut you are tightening. As soon as the nut reaches the surfaces of the y-carriage ;)

    Jakub Dolezal -

    How much friction should I encounter with these bearings? For example, if I turn the printer on its side should the build plate be able to slide to the other end with the assistance of gravity alone?

    AJS - Reply

    Hi AJS, the friction without the installed belt should be pretty low and if you incline the printer, the Y-carriage should start sliding down.

    Jakub Dolezal -

    When I get to the part that says “as soon as you reach the surface stop tightening”, should the u-bolt be resting on the bearing? I had trouble inserting the u-bolts into the holes and was using the bolts to draw them through a bit at a time. I’m not sure how tight they’re supposed to be before I go to the next step.

    Brenda Bell - Reply

    Hi Brenda, the curved part of the u-bolt should be in contact with the bearing. The bearing should be fixed tightly to the Y-carriage. We are warning about over-tightening, which will cause the deformation of the bearing.

    Jakub Dolezal -

    There is an easy way to tighten the nuts equally.

    Use a small piece of standard 80 grams printing paper and put this between the nut and Y carriage while tightening the nut. Stop tightening when you just (with a little bit of friction) can pull the paper out. Then rotate both nuts another 90 degrees.

    Klaas - Reply

    Good tip! It’s not always easy to tell when you hit the surface using those needle pliers.

    Amir Samad -

    I’m not really sure what I should be looking for in this step, so I just made sure that the bearings weren’t touching the U bolt, but couldn’t wobble out of the groove. I hope this works and doesn’t cause the bearings to deform.

    Zerg620 - Reply

    What I’ve got after completing the next step (25) where you tighten the bolts 90 degrees are 3 U bolts parallel to their bearing about a millimeter away.

    Zerg620 - Reply

    Hi there Zerg,

    in this step you should tighten the U-bolts so that they hold in place. Bearings will be fully tightened in the following step.


    Tomáš -

    Klaas: Thank you for the paper trick tip. Very helpful!

    JBFLA - Reply

    These instructions are not very precise. Mine had a bad vibration noise from the heat bed . I redid the tightening my own way and fixed it.

    Move bearing back and forth while evenly and slowly tightening the nuts. As soon as bearing will no longer slide, tighten each nut 1/4 to 1/2 turn more.

    I think if you update instructions similar to these would be much easier to follow and get proper results.

    William - Reply

    Hi there William, thank you for your feedback. We will try to update this step if more problems occur.


    Tomáš -

    I’m upgrading from the MK2S and have noticed that the U-bolt from the mk2s is about 1mm shorter then the one in the spare bag of the upgrade kit.

    André Rustemeier - Reply

    • Ensure again the nuts are tightened just to the surface and equally.

    • Check if the bearing is centered in both directions, if not slightly release the nuts and adjust its position. Then retighten the nuts to the previous state.

    • When you are ready, using pliers rotate each nut, but only 90°. This is enough to fix the bearing without deforming it.

    • Repeat these steps for remaining two linear bearings.

    There was a suggestion in the forums, to not tighten the bearings until after you’ve inserted the smooth rods in order to ensure aligned bearings. Is this a good idea?

    Zaz - Reply

    Hi Zaz, if you align the bearings using the cutouts in the Y-carriage you should be fine, you can do visual check as well. I've assembled several printers using the manual and all were fine with no need to readjust the bearings.

    Jakub Dolezal -

    This Tool for the nuts is very bad to handle

    Muck - Reply

    Maybe use the “correct” tool to tighten the nut? Pliers is Not that tool ;)

    List the Nut spanner size in the manual.

    Roger Meldal - Reply

    I wrote it in another reply, 72 tooth rachet, with 7/32 inch socket. I tightened by 45 degrees, side to side, to be safe.

    Mr Cookie -

    I think you should add how many newtons you can tighten the u bolt since some people have access to tork wrench and as a work injurd I get chills down my spin seeing you tighten with a plaer on the picture.

    Patrick Larsson - Reply

    Hi Patrick, we've done some testing, but the torque is very small and almost not measurable by traditional devices.

    Jakub Dolezal -

    We used a 5.5mm socket

    Jonathan Histed - Reply

    After getting the nyloc nut tightened to the manual tightness. I rechecked with a torque screwdriver and found it was approximately 20oz. in. I rechecked to make sure the u bolt and bearing didn’t move with my fingers.

    Chris Barney - Reply

    The manual for MK2S (step 15 Y-axis) recommends this: “On side with two bearings slide bearings to the center, towards each other as close as possible”. Why for the MK3 it’s recommended to center the bearings in the hole instead of pushing them to the side? Shouldn’t the instructions be the same?

    Marek M. - Reply

    Hi Marek, the Y-carriage for MK3 is different from the one to the MK2/S, that is why the assembly instructions are also a bit different.

    Jakub Dolezal -

    Used a 5.5 mm socket and ratchet wrench.

    The U-bolts are not symmetrical (not a perfect U), so even with even tightening, one has to be careful not to over-tighten.

    When in doubt, loosen rather than tighten!

    Andrew E. Mileski - Reply

    One of the U-shaped threaded rods in my kit wasn’t machined properly and a nylon bolt won’t fir without stripping. Where can I order another one? Or how can I fix it?

    William Gray - Reply

    I believe it would be helpful to include a small 5.5mm combination wrench with the kit for those that do not have one on hand. This gives far better control over tightening the nuts than pliers.

    Eric Bass - Reply

    My initial assembly was a bit noisy and scratchy after step 30. I went back to this step and made sure the U’s contact point with the bearing is dead center. Initially it was asymmetrical on almost all bearings.

    To make it symmetrical, untighten one nut and tighten the other in small increments while checking alignment. After that, the assembly felt much better, no roughness of Y carriage on any part of the rods.

    François Best - Reply

    What am I looking for when installing the bearings? Am I centering them then tightening the bolts just enough to stop them from moving? or should the bearings be able to move freely?

    Zerg620 - Reply

    Hi there, bearings should be tightened so that they can not move at all.

    Tomáš -

    The instructions say that rotating the bolts 90 degrees “is enough to fix the bearing without deforming [them]“ so to answer my previous question: YES. the goal is to fix the bearings by tightening the bolts JUST ENOUGH to stop them from moving and they VERY easy to over-tighten and get problems in the future from digging into and bending it.

    Zerg620 - Reply

    Just like you say :) make sure that they can not move, keep in mind that these will be going through a lots of movements.

    Tomáš -

    My u-bolts needed to be slightly stretched outward to mate with the holes in the frame. This tight fit presented no problem, but I was a bit more careful in assessing when the nuts where finger-tight against the frame. After reading the comments here, I backed off the nuts until the bearing would slide laterally and then tightened a quarter turn.

    Darin White - Reply

    Hi Darin, that sounds perfect.


    Tomáš -

    • Place the Y-belt-holder on the Y-carriage. ENSURE THE TEETH are facing TWO BEARINGS!

    • Secure the Y-belt-holder with two M3x10 screws. Tighten them fully, there are threads in the Y-carriage.

    Zdravím, zbyli mi dvě obyčejné matky. Nepatří sem z druhé strany? Naproti šroubům? :)

    Miroslav Novotný - Reply

    Zdravím Miroslave, v dílu Y-carriage jsou závity, takže nejsou potřeba. Ty dvě matky M3n jsou navíc, v dalších kitech už nejsou.

    Jakub Dolezal -

    the hole alignment in the y belt holder was about 1mm short

    Mark Abrams - Reply

    Don’t be mislead by “tighten fully”. The plastic piece breaks very easily.

    Ryan Sealy - Reply

    You are correct, my plastic broke a bit - but is it firm

    Bozidar - Reply

    Easier to just wiggle it a little to determine when it’s tight enough that it won’t move. If your worried about it still moving, maybe threadlock would be a good idea? Hmm.

    Mr Cookie - Reply

    Note M3x10’s threaded end will protrude by 3 to 4 threads on opposite side.

    craig - Reply

    • Take all the smooth rods and compare their lengths. For Y-carriage you need mid-sized rods (330 mm).

    • NOW, PLEASE BE VERY CAREFUL! Gently insert the rod straight into the bearings, do not apply too much force and do not tilt the rod!

    • If you can't slide the smooth rod easily, check the two bearings are aligned properly.

    • In case you manage to push out balls from the bearings, please count them. One or two balls are ok, if there are more of them, please consider ordering new bearings.

    The rod with two bearings wants to rotate counterclockwise several degrees each push and pull cycle. Is that normal?

    RWReese - Reply

    Hi RWReese, please can you make a video? Bearings should be tightened to prevent their movements, but do not overtighten them ;)

    Jakub Dolezal -

    Same here. I used a sharpie and marked the end of the rod. Every full push and pull results in 30 degrees of rotation for the ROD. The bearings don’t move. I think this is the same behavior you noticed.

    My suspicion is that a slight misalignment of the two bearings is putting a spin on the rod. However, the same effect occurs on my single-bearing rod though to a lesser extent. Maybe it has something to do with the “grin” of the tracks that was pointed out in earlier step’s comments.

    Cliff Miller -

    how smooth Should the root move. and should the bearing have any influences or artefacts in the movement pattern

    Patrick Larsson - Reply

    Hi Patrick, the rods shouldn't have imperfections on the surface, which affects the bearings.

    Jakub Dolezal -

    The bearings make a lot of noise when they move along the rods. I expected them to be pretty quiet, but that’s not the case. They also don’t seem to be moving very freely either. How quiet and smooth should the bearings be on the rods?

    Aric van Iterson - Reply

    Funny that the response to your query is met with silence… i received no less than 4 completely rooted LM8UU bearings with my kit ..the seals were chewed up like they had been forced onto a larger rod previously and the stainless folded edges were bent in places..replaced all of them with money from my own pocket.. cheers for the !#^&-poor QC Josef.

    craig -

    Sorry for not answering, we are working on a better system to manage the comments. In general, the movement should be smooth and without significant noise. Both bearings and rods were improved compared to MK2S. In case, the printer is too noisy, please contact our support at info@prusa3d.com

    Hi Craig, I’m sorry about the bad bearings, please contact our support as well. We are doing checks, but we are shipping tens of thousands bearings each month.

    Jakub Dolezal -

    I was also worried about the amount of noise the rods make while sliding, but one of the support guys says it’s completely normal. For reference, here’s a (bad) video: https://www.youtube.com/watch?v=p4SyyTDR...

    Perhaps an official Prusa video would help for this step.

    Alex Iribarren - Reply

    What do you mean “(bad) video?” Bad as in the bearings are bad, or bad because it sounds bad but there’s actually no problem?

    My bearings sound exactly like they do in that video.

    Travis Howard -

    To make movement smoother move the bed with your hand a few times, the bearing seem to loosen up

    ANTALIFE - Reply

    Recommended manual change: When inserting the smooth rods into bearings, hold one hand over the exit to catch any balls that are pushed-out, so you can count them.

    I’ve managed to install all 10 linear bearings without losing any balls. *\o/*

    Building in a room with a dark contrasting wooden floor sure helps to find dropped parts, and hear when you drop them :blush:

    Andrew E. Mileski - Reply

    I found that the smoothness and rotation of the rods sliding in the bearings is directly related to how tight the U-bolts are against the bearings. Loosening the U-bolt nuts one-eighth of a turn made a big difference in the feel of the rods moving through the bearings, it was more smooth and less likely to rotate the rod.

    I guess you want the U-bolts just tight enough to keep the bearings from moving relative to the frame. Your 90-degree turn may be a little too much.

    Timothy W. Skloss, Ph.D. - Reply

    Where would I buy replacement parts for the kit, such as the aforementioned linear bearings, as well as replacement printed pieces? Could I get a link please? I was a bit careless with the x axis, and broke 2 bearings and one of the x axis pieces.

    John Liu - Reply

    Agree that loosening the U Bolts nut a tad allowed the dual bearing rod to spin much more freely.

    IPT - Reply

    I found as little as an eighth turn on the u-bolt nuts make a big difference in how the rod runs through the bearing. I lost two balls from the one bearing, happily captured them because I’m building on a glass sheet. I shone a light through the far end of the bearing and could see where balls were missing, used tweezer to place the ball back in the bearing and applied very slight pressure and the ball popped back into the channel. Seems to be working ok.

    Darin White - Reply

    Hi Darin, even without the two balls you would be fine :) good that you were able to get them back!

    Tomáš -

    I found that after tightening the nuts on the u-bolts, the rods would not rotate freely in the bearings. I loosened all of the u-bolt nuts enough that the rods turned freely in the bearings. They then also moved more freely and with less noise.

    Don Bone - Reply

    My single rod bearing is much noisier and vibrates/rumbles the plate with the rod in. The other rod is pretty smooth and sounds normal or as what I would expect. Now what…there’s no spare so I need to wait a week to get a replacement bearing?

    Misiu Kowalski - Reply

    Hi there Misiu, can you please double check that you did not over-tighten the bearing which is more noisy?


    Tomáš -

    A tip: Take a permanent marker and draw a line on each bearing where the row of internal ball bearings are that will be facing to the top when the y-carriage is mounted, that way you can double check the bearing orientations after the rods are inserted and the rods are secured. These ball bearings are essential to keep noise and friction down as that top row of takes all the weight of the carriage.

    Werner Marais - Reply

    • Take the Y-carriage including smooth rods and place them in YZ-frame. Make sure, that two bearings are on the left side (see the picture).

    • Using your thumb, press the smooth rods inside all four holders. Don't use excessive force.

    • Check again the correct bearing orientation!!!

    They really don’t go in very far.

    Visually verify that the bottom of the smooth rod is seated fully in the plastic part, and you are good to go!

    Andrew E. Mileski - Reply

    I did not check this. Noticed in chapter 7 that holes did not fit heatbed.

    Dont skip stuff :)

    Tor Andre - Reply

    What happens if the Y-carriage is installed with the 2 bearings in the right side??

    Gustavo de León - Reply

    Hi Gustavo, it has to be installed this way, or you will have issues later on during the assembly.

    Jakub Dolezal -

    Thank you Jakub, I suppose it’s because the cables of the PSU.

    Thanks Again :)

    Gustavo de León -

    You’re welcome Gustavo, enjoy the build ;)

    Jakub Dolezal -

    I am putting the rails on and the u-bolts actually hit the frame if I don’t have them tightened down all the way. I am sure that’s not how it should be, but I am afraid of torquing the ubolts too hard on the bearings. Any suggestions?

    It is on the frame side with two bearings. The side with one not only seems to slide smoother, but doesn’t bump the bolts. I swapped both bearings and ubolts to ensure it wasn’t just the one side, etc.

    Ben V - Reply

    I have the same issue. Did you solve it?

    Chris C -

    • Find the package with zip ties and take out 4 pieces.

    • Slide the zip tie through the holder, there is a slot.

    • Connect the zip tie and tighten it. The "head" should be inside the frame.

    • Using pliers cut the remaining part.

    • Repeat this step in all four corners.

    I feel like something soft could be used to keep the metal rods from banging the frame if they’re loose. Just a thought.

    Mr Cookie - Reply

    the instructions show the zip tie head on the inside but the picture shows the head on the outisde. it is corrected on the next image

    David - Reply

    I thought that at first glance, but there is no issue, take a closer look :-)

    Andrew Holloway -

    Flush cutters or even diagonal cutters will make doing zip ties close to their lock much easier than the included needle nose pliers

    Mustrum Ridcully - Reply

    :-) “Find” the package with the zip ties. As if you knew that, by this time, they were at the bottom of the heap of all those plastic bags.

    Oh, and yes, +1 for the flush (or diagonal) cutters.

    Markus Imhof - Reply

    • IMPORTANT: proper alignment of the smooth rods is crucial to reduce noise and overall friction.

    • Ensure all M3x10 screws on Y-holders are released, so the printed parts are able to move.

    • Move the Y-carriage back and forth across the entire length of the smooth rods to align them.

    • Then move the carriage to the front plate and tighten all screws in the front-Y-holders.

    • Move the Y-carriage to the rear plate and tighten all screws in the back-Y-holders.

    Anything I can do if the M3x10 screws on the rear plate (short extruders) holding the rear Y-holders are not tightening all the way? They are stripped and just keep rotating. The rear Y-holders wiggle a little.

    Alex Wilkie - Reply

    Hi Alex, are you able to release the screws and take them out? Both nuts and screws, can be replaced from spare bag if needed.

    Jakub Dolezal -

    it would really help if you made a video to show how much force you should use and how it should Glide

    Patrick Larsson - Reply

    Hi Patrick, thanks for the input. Those information you asked for are very hard to be “shown”, but I will think about it ;)

    Jakub Dolezal -

    The first picture has a green arrow pointing to one of the M5x16r screws in the frame. Pretty sure that should be pointing at the M3x10 screw holding the Y-holder to the frame. Might want to take a new picture.

    Glenn - Reply

    Hi Glenn, there is a M3x10 above the M5x16r so the arrow position is correct. However, you’re right I will take the picture again from a different angle.

    Jakub Dolezal -

    when I slide the rack should I hear a raspy sliding noise? Or should it be perfectly silent?

    William Waytena - Reply

    Hi William, certain level of noise and resistance against the movement is possible. However, it should be almost the same level everywhere. In case the noise or resistance is at certain spot, try to realign the rods once more.

    Jakub Dolezal -

    Perhaps you could document or show how high (or what degrees) one has to raise the frame from a single end in order to break the force of friction with gravity as a demonstration of how easily/smoothly the bed should run. I have to raise mine about 14cm and give a slight tap. Don’t know if this is normal.

    Rich - Reply

    Hi Rich, interesting idea! I will put it to the test and see if it brings some reasonable results.

    Jakub Dolezal -

    Using Rich’s method from march 22 we had to raise the front by 7cm before the carriage slid down the rails

    Wade Tubman - Reply

    Thank you for the reference. My number is similar, a bit less than 7cm.

    Siu Chuen Chan -

    6.5mm lift for me.

    Darin White -

    6.5 cm for me also, but only with a tap hard enough to overcome the static friction. About 15 cm lift to initiate motion.

    Gordon Stout -

    6.5 seems about right for me. But I’d not give too much on that number.

    Markus Imhof -

    I had no problem with the assembly of the bearings and smooth rods. I noticed that the bearings weren’t as smooth as I thought they should be, but once the assembly was done, they appeared to be fine, with just a little roughness noticeable. Unfortunately, once the printer was functional, every print I sent through the printer came out with a Y-axis offset, and they appeared at the same height on all of the prints. Moving the bed slowly front to rear, I still noticed roughness in the movement. I disassembled the Y-axis enough to remove the bearings, then removed the single bearing closest to the power supply. Replacing it with a new bearing I already had on hand, I reassembled the assembly and found that it was very smooth. This also made the printer very quiet and noticeably smoother. It also appears to be printing a bit faster. Having been keeping track of the MK3 since it has been released, I have read quite a bit about the bearings being less than ideal. Perhaps IGUS is the solution.

    George Miller - Reply

    • There is a flat part on the motor shaft, rotate it similarly to the first picture.

    • Place a GT2-16 pulley on the Y-motor shaft as shown in the picture.

    • Don't press the pulley against the motor. Leave a gap so the pulley can rotate freely.

    • One of the screws must be facing directly against the pad (flat part) on the shaft. Slightly tighten the first screw.

    • Turn the shaft and slightly tighten the second screw.

    • Don't tighten the pulley firmly yet, we'll get to that later.

    Add Comment

    • Turn the frame on its "right" side, as shown in the picture. You need access to belt holder, idler and pulley.

    • Use the bottom opening in the extrusion and gently insert the cable from Y-motor.

    • DON'T TRIM THE BELT unless you are asked in the instructions!!!

    • Find the belt for Y-axis (Y-GT2 650 mm) and insert one end in the Y-belt-holder. Ensure you are using the upper slot (closer to Y-carriage).

    • Make sure you won't accidentally use the belt for X-axis (X-GT2), which is longer.

    • Press the belt all the way in, use Allen key.

    Perhaps add the part # for the Y axis belt? It’s labeled as Y-GT2 on the package’s sticker.

    Kalani - Reply

    There will be sticker refresh, I will ask my colleagues to add it.

    Jakub Dolezal -

    I couldn’t get the smaller Allen key to fit and the included flat-head screwdriver couldn’t get a good angle on it. I found one of the trimmed or tail ends of a zip tie worked well.

    Connor Ness - Reply

    We think it is worth adding a caution as to getting the correct belt :

    We initally assembled with the wrong belt and only found it was too long a few steps on, beware : make sure you have the Y-GT2 not X-GT2, For this step you need the shorter of the 2 belts in the kit albeit they were in different packets to start with.

    Jonathan Histed - Reply

    Hi Jonathan, the correct belt type and length was already part of the description, but I've updated the text to be bulletproof :)

    Jakub Dolezal -

    The edge of a bank card works great to get the belt fully seated in the belt holder.

    Chris Barney - Reply

    “Use the bottom opening in the extrusion and gently insert the cable from Y-motor. “

    Is this just an idea about how to keep the motor cable out of the way?

    Eyal Peleg - Reply

    Hi Eyal, it is just a temporary solution to fix the cable in one place so do you don't have to arrange it every time you move with the printer.

    Jakub Dolezal -

    using the end of one of the zip ties cut off in a previous step worked great. use it length-wise to push belt in evenly.

    John Green - Reply

    slotted screwdriver is no longer provided so should remove reference to it in last bullet.

    Rick - Reply

    Thank you, updated.

    Tomáš -

    I am not sure what the ygt2 650 mm looks like and where I find it this seems to be a problem.

    Zachary Goldberg - Reply

    Hi there Zacahary, you have 2 different belts included in your kit, just make sure to use the shorter one for this step. Longer one will be used later on in the assembly.


    Tomáš -

    • Insert the belt through the idler as shown in the picture.

    • Guide the belt behind Y-axis motor and ensure following:

      • Don't use the second slot in the Y-belt-holder.

      • Guide the belt above the aluminum Z frame, NOT below.

      • Guide the belt above the rear plate, NOT below.

    • Turn the printer on its "feet" and guide the belt around Y-motor.

    The part “Don’t use the second slot in the Y-belt-idler” might need to be corrected. I’m assuming you mean the second slot in the Y-belt-holder, not idler.

    Paul Betz - Reply

    Hi Paul, you’re right. Thanks for the feedback :)

    Jakub Dolezal -

    Hi, the y-belt-holder part which came with my machine is way too loose on the upper slot - the belt slides out while tensioning like in step 36. I printed out a spare part - and guess what it has original the same problem ?

    What was wrong with the old belt holder - the way to hold the belt with itself is simply the best solution.

    Richard Rohan - Reply

    I had to reverse the pulley on the motor to get it to center with the belt as the bed moved toward the Y-motor. With the pulley as shown in the picture, it needed to be up against the motor and I was still getting a little rub on the pulley side. Yes, I have the belts pushed all the way down into the slots. I was able to get the belt to run in the center of the pulley with the end of the motor shaft flush to the pulley with the pulley reversed. There was still plenty of room to get the set screw on the shaft flat.

    Mike Malpass - Reply

    I found that using the tiniest Alan wrench key helped me “flip” the belt around the idler. I found that the belt kept getting caught on the nut.

    Zerg620 - Reply

    • Hold the Y-carriage by hand (prevent its movement) as we need to pull the belt.

    • Ensure the idler isn't tightened completely to the front plate. Otherwise, you won't be able to adjust the tension later.

    • Take the end of the belt, pull the belt with a reasonable force and insert it in the Y-belt-holder. Note you don't have to use the whole length of the slot.

    • Press the belt all the way in, use Allen key.

    • The belt should be stretched and not easily bent. However, the final tension will be adjusted later.

    If you use 14mm (i use 16) screws for the idler on the front plate, you can take the end of your belt easy in, and you will have a lot to screw & tight later ?

    Jeremy - Reply

    Hi Jeremy, our aim is to reduce amount of screw sizes. That is why M3x10 used.

    Jakub Dolezal -

    anyone elses 650mm belt only 590mm long??

    Tim - Reply

    Hi Tim, belts must be 650 mm (Y-axis) and 850 mm (X-axis) long. Anything shorter won't work. Please contact our support (info@prusa3d.com).

    Jakub Dolezal -

    If the belt is longer than needed (more than 5 cm longer) then you have the wrong belt (there are two belts). Certainly don’t cut the left over part.

    Edwin Martin - Reply

    I’m on my 2nd MK3 kit and the teeth in the Y-belt holder were way too loose in this kit. Belt is hopping and slipping teeth inside of it (as evidenced by my bloody knuckles while trying to tension the belt).

    Connor H - Reply

    No slotted screwdriver anymore. Should remove reference in last bullet.

    Rick - Reply

    Thank you Rick, updated.

    Tomáš -

    I’m sure this is obvious, but in the previous step it said to turn the printer back onto its feet, but to insert the last part of the belt (in this step) back into the Y-belt-holder, we need to rotate the printer back onto its side, correct?

    Adam Timmerberg - Reply

    That’s correct.

    Filip Misiło -

    • Make sure the belt is placed in the "axis" of the printer. Both top and bottom part of the belt should be parallel (above each other).

    • To adjust the belt position, release screws on the pulley and slightly move with it, until you reach the best position.

    • In case you can't make the belt parallel, check if the belt is properly inserted in the Y-belt-holder (below Y-carriage).

    • Tighten both screws on the pulley.

    As a note, there’s no usable adjustment space in my build for alignment; the belt is against the right side of the idler pulley, the motor pulley is up against the motor, and the belts are at full depth in the holder; I had to be careful to leave a small gap between the motor pulley and the motor, it would have been very easy to accidentally tighten the pulley up right against the motor, trying to get the best alignment. (And that would be bad, because they could bind.)

    To gain some space to adust, the motor mount would have to position the motor more to the left, and the idler pulley mount needs to be more to the right. These are Prusa-supplied Orange parts.

    Kenneth Albanowski - Reply

    To avoid eye-balling the perfect alignment I just loosened up both set screws of the motor pulley so that it would rotate freely on the shaft and moved the Y-Carriage back and forth along the full-length Y rods until the belt adjusted itself on the idler and on the motor pulley, on this side also moving the pulley with it along the shaft, as necessary. In my case the belt is flat against the idler on the opposite flange to the Y motor while the idler is also flat against the plastic part so a wider gap on the plastic part could be appropriate.

    After I was satisfied with the alignment I moved the Y-carriage until one set screw came just above the motor shaft’s flat side, where I fastened it. Then I fastened the other set-screw.

    Florian Ford - Reply

    Really struggling to get the belt to align as its rubbing on the pulley lip close to the motor.. It seems like the motor needs to move a few mms (away from the pulley) as you the pulley hits the motor before the belt runs centrally on it.

    So I have created a spacer which moves the motor 2mm… And it appears to have done the trick.

    Others on teh forum have confirmed this, so I believe Prusa need to consider changing the mount to move the motor slightly, allowing more of the shaft to be useable.

    For now I have made a 2mm spacer which appears to have done the trick:


    Jon Weaver - Reply

    If the pulley screws are not tightened really properly, it may cause a random y-axis layer shifting later!

    Miroslav Piencak - Reply

    I found that in step 21 how you tightened the motor bracket can have an impact on getting the belt aligned. I had the pulley spaced from the motor with a piece of paper, but the belt still rubbed on the motor side of the pulley. So I loosened the belt, and then loosened the two bolts holding the motor bracket in place. I then pushed on the bracket so the motor and bracket was as far to the direction opposite the motor shaft as it could go. Then I tightened up the bolts for the bracket. This moved things enough that I could adjust the pulley and get the belt to not hit the side of the pulley.

    Wayland - Reply

    I'm not sure if  its normal or not but the belt wonders left to right on the motor pulley but mostly rubs against the motor side of the pulley. I tried everything I could think of from readjusting the motor and mount, flipping the pulley and toothed belt holder, tightening or loosening the belt until I noticed the motor mount bracket isn't exactly a 90 degree angle, its slightly bent in witch angles the motor making it unparalleled with the frame and creates the pushing and pulling of the belt left to right. So either a new bracket has to be printed out or shimming is need I’m pretty sure.

    Chad - Reply

    I have the same issue and tried loosening and moving everything. I eventually turned the pulley on the motor shaft around and noticed that no matter what, the belt would move back and forth on the pulley and rub on either side.


    The Y-motor-holder is the real culprit.


    Thy this: Facing the front of the printer, place your right thumb on the body of the motor and hold it against the rear plate. You will feel slight movement of the Y-axis motor. Hold the motor in this position and move the Y-carriage towards you until the bearings hit the front plate. Notice the position of the belt on the pulleys. Notice that the belt’s position on the pulleys as you move the Y-carriage towards the back of the printer stays fairly consistent, comparatively. This eliminated almost all movement for me, but what’s the solution?


    I was thinking about adding a zip tie, but haven’t gotten far enough into the assembly to be confident that it won’t interfere with something else. Any suggestions?

    Travis Howard -

    When aligning the belt I also had an issue of it rubbing against the left side of the pulley. I used a spare piece of belt I had remaining after assembling the X-Axis, which I placed inbeween the frame and pulley holder on the right side of the screws. Now I can subtly adjust the screws and correct the belt alignment if it starts tracking incorrectly.

    Allen Cole - Reply

    I used the 4 M3wp nylon rings from the spare kit as spacers to mount the motor to the frame. This did the trick, otherwise the belt is rubbing more than I’d like. Please get this fixed in the next iteration.

    Zsolt van den Mar - Reply

    +1. Yes, this helps. Still a little wander but less.

    Twerd -

    I am also seeing the issue with the belt rubbing on the motor side of the pulley. Not sure if I’ll shim or flip the pulley….

    Rich - Reply

    On first attempt my belt’s sitting up against the left side of the pulley. Going to try some of these suggestions here. Starting with the spare 18mm’s on the pulley to give me more wiggle room. Seems the 10mm screws can barely get two threads anyways. I think it’s because the nuts sat high in their impressions in the pulley side.

    Todd Scott Anderson - Reply

    The belt looks very close to parallel now, but it still wants to move toward the motor. On close inspection of the motor’s position, it is not exactly parallel to the frame. The motor mount holds the server out at a very slight angle. The servo seems to be about 0.4mm off the frame by the mount, and 0.8mm off the frame at the end.

    After retightening the screws mounting it to the motor, and the frame, I don’t see improvement.

    I’m worried I may have overtightened one of the frame mount screws, but it still seems solid so I’ll leave it.

    Next I’m going to join 3 or 4 zip ties together and will use them to pull the end of the motor closer to the frame. Maybe it’ll find a solid and stable position that’s closer to parallel.

    Todd Scott Anderson -

    The motor is mounted much more closely to parallel with the frame now. I had to use 3 zip ties in order to avoid having a nub protruding up top which would get in the way of the carriage. Couple spots of hot glue to keep the zips in place, and I’m happy with how it is for now. The belt’s top and bottom seem to be in line, and there’s a tiny bit of play on the idler pulley but the belt seems firm enough.

    Looking at it from the idler pulley, the belt sits on the right of the idler and the left of the gear pulley. Used a paper to space it off the motor. Both ends of the belt are tucked in deep on the center piece.

    Todd Scott Anderson -

    Zip ties the motor to the rear plate did reduce the amount the belt moving! Thanks!

    getabyte1432@gmail.com -

    I also had the alignment issue on the motor pulley. It was cause by the motor not being mounted flush against the frame. Loosening the screws that hold the motor, pressing the motor against the frame, and retightening the motor screws fixed this.

    Etienne van Ballegooijen - Reply

    We had the same problem with the belt touching the pulley on the motor side. We turned the pulley round, the grub screw can tighten on the motor shaft ok, and this gives plenty of adjustment on the pulley on motor shaft position, which doesn’t exist unless the pulley is turned round. (and itthe pulley’s position has had to move out about 3mm)

    We found as the carriage is pushed back and forth, the belt winds from one side of the pulley to the other at each extreme of the carriage movement. We’ve concluded this is probably OK but something can’t quite be lining up, or perhaps there is a very very slight asymmetry in the belt. or the machined surface of the pulley to produce this effect. The bulk of the time the belt is running in the middle of the pulley wheel, missing both sides.

    Jonathan Histed - Reply

    In this step, Aligning the Y-Axis Belt, you’ll notice that many builders have had problems with belt alignment which is causing the belt to rub against the pulley; I was no exception.

    The fix for me was to trace the outline of the motor mount (specifically the side that faces the motor) onto a piece of 20 AWG brass. I cut this out using a jeweler’s saw and a drill press for the holes then, after some de-burring, I successfully used it as a shim between the motor and the orange bracket. This added enough of a re-positioning of the motor so that the belt no longer rubs against the pulley. Also, I used a feeler gauge to offset the pulley from the motor’s surface 0.005mm. YOU might find that a thicker gauge shim will work better but keep in mind you don’t want to weaken the screw to motor connection; you might need to buy some longer screws and cut them back as needed.

    D Evers - Reply

    The body of the stepper motor is not flush with, nor below, the edge of the mounting bracket. So the stepper motor body levers away from the frame, causing the belt to climb towards the stepper motor. [Belts always climb to the shortest side / path of least resistance.]

    Mounting the bracket first, tightening it securely, then mounting the stepper motor, and gently tightening its mount screws, solved the alignment problem.

    For a bit more adjustment, clean-out the stepper motor mount holes in the bracket, as they are very tight, and do not allow for much play.

    Andrew E. Mileski - Reply

    same problem here…. I think I’ll turn the pulley

    jorgemarmo - Reply

    My motor gets bent a little bit away under tension.

    Obviousley, the motor bracked is not sturdy enough.

    This makes it difficult to get the belt in the middle of the pulley .

    Motor mount shoud maybe made of steel or alloy.

    nikolaus.brandtner@gmail.com - Reply

    Here, belt touches the motor side, too. The motor holder need a new version model, keeping the motor away from belt for more 2 mm. It’s already August, though.

    Hsiung - Reply

    I had the same issue of belt rubbing against motor side pulley edge. The fix for me was fairly simple. I loosened the 2 bolts holding the motor mount to the rear plate and used a piece of zip tie (cut from previous step) as a shim by slipping it between the motor mount and the rear plate. The zip tie is placed vertical, slipped in from the right side (assuming your looking from the front to the rear) and rests next to both of the motor mount bolts. Then tightened the bolts again. This pushes the right side of the motor out away from the frame and is just the right amount to keep the pulley belt in the center of the pulley.

    Rick - Reply

    Thanks for your simple but ingenious idea, Rick. That seems to work for me.

    David Day - Reply

    Turning my assembly upside down and looking at the belt track as the carriage got closer to the motor mount showed that like other people noticed the motor mount does NOT hold the pulley perpendicular to the belt so that makes the belt track badly. The other problem seems to be caused by the Y Belt Holder. I can’t get the belt in far enough to let it track smoothly even if I shim out the motor and fully recess the belt with a thin debit card. I messed around and broke the Y motor mount trying to get it to track properly. Hopefully some CA glue will get the thing going again until I can print another. It seems like there needs to be a bit more adjustability modeled into these parts. Slotted holes or something. Because without jury rigging shims or something I can’t get mine to line up.

    Rich Rector - Reply

    I too am having belt tracking issues while moving the bed back and forth, not sure if the issue will remain when the motor is powered and driving the belt but I concur with Rich Rector that the motor mount is just not quite stable enough and the belt tension causes it to flex. There are several good fix ideas noted here but a design fix would probably need a rear motor mount added to keep the motor Axel on plane. Might be my first project with this printer.

    Doug Kline - Reply

    Hello! As long as it stays in the pulley, it is still OK if the belt is moving sideways by -/+ 1or 2 mm. However, we understand your point and we’will pass this message to our designers/developers.

    Martin L. - Customer Support -

    Clean pulley set-screws with rubbing alcohol and use a tiny bit of blue loctite to hold them in place…

    Jack - Reply

    Chiming in here about the issue with getting the belt to stay parallell.. I ended up inserting shims between the servo and servo holder to move it a bit further away, allowing the pulley to be adjusted 1mm more towards the servo side.

    The belt will still wander about 1-1.5mm as you move the carriage between front and back.

    Design needs to be improved.

    Patrick Winnem - Reply

    • Using Allen key tighten/release the screws on the front plate. Try to adjust both screws the same way.

    • Using a finger on your left hand push the belt down. Some force should be needed for bending the belt, BUT don't try to overstretch the belt as you might damage the printer.

    would it be possible to know. the belt tension. and should you leave some room so that you can tighten it when it gets loose over time ?

    Patrick Larsson - Reply

    Hi Patrick, the proper "value” of the tension is something we are working on. If the Y-belt gets loose over time (this shouldn't happen earlier than after one year of heavy usage), either tighten the idler more or use Y-belt-holder and move the belt be tooth or two.

    Jakub Dolezal -

    One way to let users know how much tension should be on the belt might be to have us hang something of a known weight (perhaps one of the other printer parts) from the middle of the lower belt temporarily, and tell us how much the belt should deflect.

    Frank - Reply

    Or just mention the amount of belt deflection with one of the parts in the kit sitting on the belt

    Mike Katz - Reply

    Hi Frank and Mike (@frank, @mike603), thanks for the suggestion I will test it and if it works well, update the manual.

    Jakub Dolezal - Reply

    As a measure of tension, what frequency of sound should the top and bottom part of the belt produce when plucked? Or does this mean mine is overstretched? :)

    Christophe Lermytte - Reply

    I would have appreciated more guidance as to the proper tension here as well. Thankfully, I had access to someone else who had built a printer. In my case he thought I had tensioned the belt too much and suggested backing it off a tooth. This step is pretty subjective in ability to judge correct tensioning.

    Kris Boyle - Reply

    Ahh Belt tension the question that is asked all of the time in the DIY CNC and 3d printer community and one solution is using a luggage scale and a ruler. What you do is move the carriage or extruder all the way to one side. Then find the center of the belt between the (Carriage/Extruder) and the opposite end by the pulley this is where you will place the luggage scale hook. Put the ruler behind the scale to see how high to pull the belt up. For these types of belts I would pull it up to 1/2” at this point the scale according to my current tension is around 1.5 lbs for a 1/2” belt pull up. If we can get a tension rating off of this technique then it will give us something to go buy like many have figured out with my cnc machine (which is a different pull up and lbs used do to the length of the belt.

    Kris Sovers - Reply

    Hi Kris, thanks for sharing this approach. We need to use tools, which are in the kit, but I will do some tests this week.

    Jakub Dolezal -

    I like this approach. I would certainly be willing to go out and buy a cheap luggage scale to get this right. I also imagine it would be useful in just checking the belts for periodic maintenance.

    The fact that it is from another Kris has nothing to do with it… :)

    Kris Boyle -

    I pulled the belt by hand as much as was reasonably possible. To engage the next tooth, I’d probably have to hold the belt with pliers, i.e. I think that would be too much tension.

    The idler is secured flush to the frame, as though the small gap aids in reducing tension while installing the belt (it is about a belt-tooth wide), but doesn’t seem to contribute greatly to overall belt tension.

    Andrew E. Mileski - Reply

    I would suggest using some sort of washers or shims in step 18 to ensure consistent gap. This will also make it easier for those who don’t get the “correct” vs “wrong” pictures. Thick just enogh so that the belt end slides into position in step 34 effortlessly without using force. Remove washer(s) or shim prior to step 36 and you should achieve consistent belt tension without the need to check it using additional equipment to measure deflection.

    Marek Stenky - Reply

    Hi Marek, thanks for the suggestion. The gap is designed to allow the belt tensioning, adding the washers, would decrease this gap.

    Jakub Dolezal -

    To properly perform this test, we also need to know at what position the Y-carriage should be in. If it is at the back, there is considerably more slack/flex added to the belt than if it is in a middle position.

    Should this level of tension exist with the carriage all the way to the back (or to one end)?

    Connor H - Reply

    I found that tightening the tentioner fully, then back off each screw 2 turns worked perfectly for me.

    Bill McKay - Reply

    • Use the technique described below to test if the belt is properly stretched.

    • Use pliers to hold the Y-axis motor shaft.

    • Move the Y-carriage with your hand towards the Y-axis motor. Don't use excessive force.

    • If the belt is stretched properly, you should feel a resistance and the Y-carriage won't move at all. If the belt is too loose, it will deform (create a "wave") and jump over the teeth on the pulley.

    My belt was too loose. The screws for the y-belt idler should be loose when completing step 34. After connecting the second end of the belt, you can then use the screws for the y-belt idler to tighten the belt.

    HCruse - Reply

    Hi HCruse,

    this covered at step 18: 2. Y-axis assembly

    Jakub Dolezal -

    “Move the Y-carriage towards the Y-axis motor. Don't use excessive force. “

    I would recommending this to Move the Y-carriage towards the Y-axis motor by hand. Don't use excessive force. “ And show a hand on the Y-carriage.

    Mike Katz - Reply

    Hi Mike, text updated. Regarding the photo I think it is clear, what to do. Thank you for the suggestion.

    Jakub Dolezal -

    On mine, the motor pulley is full left on the shaft, with the belt as far left as it will go on the pulley. Everything seems to move well, but I’m concerned some about belt wear over time. Tension appears correct; slight deflect with a moderate finger push, no slippage when holding the motor shaft still. I guess time will tell.

    steve hix - Reply

    I started my build last night and I am at the same point. The Y belt is parallel and the bed moves smoothly. However the belt is hard against the 'left', motor side, of both the pulley and idler. There does not seem to be any deformation of the belt on either. I'm curious if it is supposed to run centered.

    Jon Duke -

    It is much better to put allen wrench in set-screw on pulley to hold it than using pliers on shaft for step 37

    William - Reply

    I have the same issue with the belt not wanting to sit midline on the cog. It would be nice to have an oblong hole to adjust the y-belt holder or perhaps allow the current Y-belt holder to be rotated 180 degrees and allow the cog to be mounted further down the shaft of the motor.

    Bill Hines - Reply

    Hello Bill! I hope this won’t sound too stuck-up, but this setup has been tested thousand times and is proven functional. If you have problems with aligning the belt, please make sure the Y-carriage and the plastic belt holder attached under it are installed the correct way.

    Martin L. - Customer Support -

    • Y-axis is done, great job! Open the bag with Haribo gummy bears and treat yourself with few ;)

    • Check the final look, compare it to the picture.

    • Ready for more? Lets move to 3. X-axis assembly

    The Y Axis feels somewhat “grainy" and requires a little force to move. Is this expected?

    I've been very cautious about how I tighten everything.

    Tyler Harding - Reply

    Hi Tyler, certain resistance is OK, but it shouldn't be too big. If you have issues during self-test or prints, adjust the tension by releasing the screws on the idler.

    Jakub Dolezal -

    No more gummy bears…:-(

    Jeremy - Reply

    Already eaten?

    Jakub Dolezal -

    Yeah, I screwed up… I open the gummy bears on step 1.

    Luis -

    Hi Luis, you have to stick to the instructions, or there will be consequences! :D

    Jakub Dolezal -

    Me too man me too….Can I get a replacement for the gummy bears?

    Marijn -

    I still have gummy bears! BONUS!

    Nick Nikzat - Reply

    Ummm… gummy bears got used up during the unexpected 33 hours of printing for the mk2s to mk3 upgrade kit parts! Should have sent 2 bags dude.

    David - Reply

    At the end I had some belt skew … in order to get it straighter I needed to file off a little of the tabs on the bar holders on the long extruded side so that they could shift a little left/right.

    Rich - Reply

    Terrific manual, I love the attention to detail, and the humour along the way. Please don’t take on going suggestions as anything other than constructive criticism. Well done.

    Jonathan Histed - Reply

    Hi Jonathan, no worries. Your feedback is always taken in positive spirit in order to make the manual even better, so thank you for your comments ;)

    Jakub Dolezal -

    This step just made my day. :-)

    Jennifer Krull - Reply

    Those gummy bears are not suitable for Vegans/Vegeterians…

    Just saying.

    Eyal Peleg - Reply

    No reminder re: the rubber feet you were going to remind us about in step 11. Super manual. Bravo!

    Gary Shumway - Reply

    Very impressed with this manual, also comments are very helpful, thanks!

    HugoB - Reply

    Great instructions, thanks Jakub. Also really appreciate all the comments from builders. That was the best advice from a friend who strongly suggested using the online build instructions (vs the printed copy) and reading the comments. So thanks to everyone who submitted comments.

    Darin White - Reply

    Hi there Darin, thank you for your feedback :) enjoy your 3D printer!


    Tomáš -

    Wait, I wasn’t supposed to finish the gummy bears as soon as I opened the box? Oops. Well, I had to go to the grocery store and pick up more Harbios, because you can’t skip steps on a build like this.

    Adam Timmerberg - Reply

    I had problems with this step. My kit came with Haribo Dinos. I ate through every last tasty Dino searching for the bear mentioned in the instructions, but couldn’t find a bear anywhere in the package. I finally had to source my own Haribo bears locally in order to complete the step properly. If this was some sort of intentional replacement in the kit parts, the user should be warned about this well before mentioning things little things like the type of PEI sheet they’ll receive. That said, after locally sourcing some authentic Haribo bears, I was able to complete the Y-axis without further incident.

    michael - Reply

Finish Line

905 other people completed this guide.

Jakub Dolezal

Member since: 02/20/2017

112,986 Reputation

161 Guides authored


I am left with 2 extra M3n nuts (hexagons)

Alex Tramiel - Reply

Hi Alex, thanks for the feedback. For this chapter you need two M3n nuts to place them in the Y-motor-holder.

Jakub Dolezal -

Same here, two extra nuts.

Scott -

I also have 2 extra M3n nuts.

Brandon Oprendek -

Same here, two extra M3 standard nuts. All nuts are properly inserted in the printed parts, no screws are lacking nuts. Maybe can be put on the opposite side of the y-carriage to lock in the bolts holding the Y belt holder? Not necessary, but maybe optional?

Kaina Cockett -

Hi Kaina (@dracx), there are two extra nuts as a result of a design change. For the future kits it is already sorted out.

Jakub Dolezal -

i got spooked to XD well, back to work !

Vlycop Doo -

Two extra nuts here as well. Better two extra than too few!

Mike Malpass -

Thanks everyone for confirming that there are 2x M3n nuts left over. Same here! I got to the end and was paranoid that I missed steps.

Daniel Lee -

One of the short extruders lacked threads in one of the holes.

Tried making the threads with a screw and destroyed the screw head. Had to saw off the screw and try again. Not fun.

Also, aligning it perfectly was a pain

Kenneth - Reply

Hi Kenneth, do you mean the aluminium extrusions? In case of a missing thread I doubt you can create it just with the screw. In general, if there is a faulty part, please contact our support at info@prusa3d.com.

Jakub Dolezal -

Took 3hrs on the money. Moving at a casual pace with my sons help.

Scott - Reply

45 minuets for this part.. should be good for 1 hour on estimate time frame for completion.

danbrewster - Reply

2h with reading everything very carefully.

Guntor H - Reply

Is normal a kind of friction of the rods passing through the bearings?

Peter - Reply

Hi Peter, some friction is always present, but it should be smooth and without significant resistance.

Jakub Dolezal -

90 minutes for me. Would have thought the “suggest a time” would actually work up top.

Eric Proces - Reply

80 Minutes here. Two Extra M3n nuts here as well.

Douglas Shelfoon - Reply

2 hrs and spent almost 45min just to readjust ‘on flat surface’ (Step 5), it was just moving very slightly when I tap on it and it bothers me, couldn’t fix that 100% because it’s impossible to adjust them the way the screws are aligned (step 3 and 4). I also have 2 extra M3n nuts.

Cedric Young - Reply

The frame does not perfectly align to flat surface, have verified this on 3 new printers.

The only way i could get it to stop wobbling is to expand the screw holes from 5m to 5.5.

After this it is perfectly flat.

Tom - Reply

Had the same issue with it not being perfectly flat. Instead of expanding the holes I lifted the whole frame up and tightened the screws while bending down the extrusion that had been the culprit before. Got it completely flat using that technique.


Uli Braun -

Had the same issue with alignment but instead of drilling the holes up I lifted up the whole frame and tightened the screws while pressing / bending down the extrusion that had been the culprit before. Got it completely flat after that.


Uli Braun -

@tomt, can you call out which holes you opened up? Was this for all holes that the extruded aluminum parts attach to?

Martin Stoufer - Reply

Took about an hour. Leveling to the table involved loosening screws and pressing front and back down fairly hard to level while tightening the screws. Took two people, one to hold the frame flat, the other to tighten the screws. The ‘gap’ was quite small, but I guess I’m a perfectionist. Also, had the same two screws everyone else had.

The linear bearings slide, but there’s a surprising amount of noise and resistance sliding a single linear bearing on the rod compared to my other 3d printers (Ultimaker, FlashForge). i don’t think it’ll cause the printer to not print - it’s not jamming, and I am sure the stepper motors can push through the resistance, it just “feels wrong” - but if it stays this noisy and resistant after it seems some real use, I will probably replace the linear bearings just to quiet the printer down.

Laird Popkin - Reply

Hi Laird, any news on the extra nise from lienar bearings? Mine are noisy too, but i cannot compare it to anything.

Bozidar -

Hi ! I wouldn’t describe the difficulty as ‘Moderate’ - I came home to find that my 9 year old had completed this stage without any help. It was all correct too apart from needing to tighten a few things up.

Lee Massey - Reply

Hi Lee, yes this is quite an easy chapter, I will adjust the level of difficulty.

Jakub Dolezal -

1h 45min, would have been less hadn’t I managed to assemble the frame backwards - despite having read this manual at least three times. ^_^

Zaz - Reply

2 hours to complete with small brake.

Joe P - Reply

Brilliantly written instructions, went smoothly. Enjoyable experience, like meccano for grownups.

Henry Casson - Reply

Excellent instructions! A little over 1 hour but who’s counting? I’m having fun and that is good enough for me. My wife won’t let me have any of the Gummi Bears. Says playing with this is treat enough for me. The Bears are for her!

Dennis Terry - Reply

Completed section 2. I have 4 extra M3n nuts left over and I was short 2 M3Nn nuts (Which I was able to get from the spares bag).

Mike Katz - Reply

I had the same

Tony Cacciarelli -

I cheated and opened the gummi bears at the beginning before I had read through to the end of this chapter

Benjamin Johns - Reply

Noted Benjamin, you are on my watch list! … :D

Jakub Dolezal -

Section 2 still have two M3n extra bolts in the package and on the package label.

Christian - Reply

Hi Christian,

we are aware of this, it will be fixed.

Jakub Dolezal -

I suggest that for the step where you align the pulley on the motor, to adjust it in or out until the belt is not rubbing on either side of the pulley. Test this by pushing the Y axis back and forth and seeing where the belt rides on the pulley.

Also, the bolts that hold the idler wheel are too short to engage the nylock part of the nuts. So I’m not certain that the Y belt tension adjustment will hold because the bolts can turn rather freely.

I had to use a sharp knife to clean up a couple of the slots for the square nuts; other than that all the printed parts seemed to fit perfectly.

Jay Sinnett - Reply

My Y-axis took about 2 hours to assemble, but I was triple-checking every step and had a ton of issues with bolts not engaging nuts when attached through the frame. By the fifth time this happened, I started tightening down the bolts all the way through the nuts before attaching to the frame to pull the nut all the way into the printed part. This fixed 90% of my issues for engaging the remaining nuts. Just too much friction in the holes when you initially press in the nuts.

Roger X - Reply

Hi there, I got myself an fully assembled Unit. After a few Weeks my y-axis rattles when the bed is hot (I print PETG with default settings).

I think this comes from the U-Bolts holding the Bearings (Step 24). All other screws seem to be tight. How should I do this? Heat up the Bed and tighten the nuts slightly?

Thanks, Ralf

Ralf W - Reply

Excellent Directions

Doug Tanner - Reply

Finished this step in about 30 minutes, had to use a thread chaser on a few of the threaded holes in the frame.

Ricky Burnett - Reply

Finished with no significant issues

Pascal Scheffers - Reply

Its an very good discription to bild the printer

Roelof Veldhuizen - Reply

A little less than 3 hours, but I read each section carefully, double-checked parts, etc. I think my husband was disappointed I didn’t have to ask him for help, LOL.

Brenda Bell - Reply

Oh, I thought the Gummy bears were 3d printer parts. ;) Joy to build so far. Step 10 a pain, thank you Paul, I owe you a beer. Something does not seem right that so many struggle with that critical step. Took about 1 hr for this part even with the step 10 multiple attempts. This online manual really helped.. anytime I was questioning the step if I really understood, I read the comments, and likely avoided problems.

also thanks to all who posted.. I any step that had lots of comments, I slowed down. read the comments and got it right the first time.. except step 10. LOL

Jonathan - Reply

In the steep 28 what happens if the Y-carriage is installed with the 2 bearings in the right side??

Gustavo de León - Reply

Hi Gustavo, as explained in the step 28, it has to be installed as instructed.

Jakub Dolezal -

About 1.5 hrs spread over a couple days, two M3n nuts left over. Good documentation so far (says 40+ year working tech writer). No Haribo left.

steve hix - Reply

Hi Steve, thanks for the feedback, though with the gummy bears it seems to me, you were not following the instructions properly :D

Jakub Dolezal -

Took about hour and a half. belt seems kinda tight but loosened the pulley. see how it goes. And no Hairdo for me. Wife ate them before step one lol I was trying to save them.

Antonio Hermosillo - Reply

I’ve just finished this step. But Y-carriage make too much noise when I moving it by hand. Can anyone suggest is it because of tighten belt or there other reason? Also there something strange. When I moving Y-carriage with relatively same force Y-carriage moving with different tension in two positions as you can see in clip.

Video clip of moving Y-carriage by hand after assemble: https://www.youtube.com/watch?v=Ix7rvUYH...

Dmitriy Lekomtsev - Reply

Mine sounds the same as yours in your video. I see you built in July. Did it turn out to be OK?

Rick -

I think not moving smoothly when belts are connected is caused by cogging in the y-axis motor, which is expected.

Nicholas Sherlock -

It feels a bit saddening that a lot of great comments did not generate a feedback loop to development (or even to QA for handbook updates) in a timespan of almost a year. I always had to mistrust each step and read the comments first. This is not the way a documentation should be written.

patrick.fehr@fbc.ch - Reply

So far, the guide is excellent! The only part I don’t like is the tightening the ubolts for the yaxis bearings; getting that wrong and invisibly damaging your bearings doesn’t fill one with confidence. A 3d printed nut-driver that visibly flexed when you got to the desired tension?

Eric Davies - Reply

Hello, it is normal that the bearings leave a small mark of grease at the end of the travel on the smooth rods? Thanks !

Israel - Reply

I found a 5.5mm nut driver extremely useful, especially for mounting the y linear bearings.

One bit of information that would have been useful would be a ball park torque spec for the 3mm screws on shaft holders.

dogma - Reply

I agree and in the US an XceLiteP-7 small nut driver works for these unlocks, it makes this step much easier. I would not want to try it with spring loaded needle nose pliers. The right tool for the right job.

Mustrum Ridcully -

My gummy bears came melted to one big gummy bear chunk…

Timofei - Reply

Hi there Tim, I am really sorry to hear that :/ must have been a fault of the delivery company. As the boxes ready to be shipped are always stored in our warehouse prior to shipment. I hope it did not spoil the assembly much.


Tomáš -

Step 10 is physically impossible. Should I resort to redrilling holes for more tolerance to remove the slight wobble?

Rob Hinojosa - Reply

Paul’s comment worked. Had to use weights instead of clamps though. Please, for the sake of us users, please add his tweak to your instructions.

Rob Hinojosa -

No issues for me. Great instructions Jakub! My granddaughter got ahold of the dummies so I didn’t have any to feast on.

Doug Kline - Reply

Spoiler Alert: You are going to reevaluate your self control on step 38.

Adam Timmerberg - Reply

No issues with this part, took maybe 2 hours total.

Matt Laudato - Reply

Nobody uses blue loctite on metal to metal threads?

Jack - Reply

I used red (medium) Loctite on all screws that should never need to come out. After seeing how my MK2 vibrates sometimes I thought it may be a good idea.

Ybl84f1 -

Fantastic way of providing instructions…a printed manual, an online (latest info) manual with high res pics, and a comment section. Really brilliant, well done!

Ybl84f1 -

Removed all printed items from bags/boxes, cleared all print dust from all orifices and micro drum sanded all fastener nut slots, filed all nut holder orifice grooves so nuts wouldn’t round out any printed parts. Checked all threads in all metal parts and deburred and lubed all threads.

Prep time = 4 beers (done a couple days ago)

Y-axis assembly time 44 minutes zero problems (done today)

will start next section in a day or two

fantastic quality on all items and instructions, just wish time was on my side

Randy Davis - Reply

+1 for measuring time in beers!

Martin L. - Customer Support -

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