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

    • 2.5mm Allen key for M3 screws

    • 2mm Allen key for nut alignment

    • 1.5mm Allen key for tightening the pulley

    This section took me 4 hours and 45 minutes. That included a half hour to grind the head off a bolt so I could remove it after the nut I was pulling in with the bolt started spinning in it’s socket. I don’t recommend the Prusa method of pulling a nut into it’s socket with a bolt.

    Keith Selbo - Reply

  2. This is the most important and hardest chapter, take your time, don't rush. Properly assembled extruder is essential. The bag with fasteners includes M3x20 and M3x18 screws make sure you won't mix them! Pay attention to the instructions, when to use the M3x20.
    • This is the most important and hardest chapter, take your time, don't rush. Properly assembled extruder is essential.

    • The bag with fasteners includes M3x20 and M3x18 screws make sure you won't mix them! Pay attention to the instructions, when to use the M3x20.

    • Keep the magnets apart in a sufficient distance. They can break each other!

    • The hotend for MK3S needs a shorter PTFE tube compared to the MK3 (more info here). Make sure you have changed it.

    • Pay great attention to the cable management, if you miss some important step you would need to disassemble the extruder.

    • This bag includes extra fasteners and printed parts. Don't worry if you finish with few unused items.

    Couldn’t find the two M3x20 in the fastener bag but located them in the “5. E-AXIS - MK3S” bag

    HugoB - Reply

    The green arrow points to a cable tie. It probably should point to the PTFE tube, which is hardly visible white on white.

    Christiaan van der Veer - Reply

    Thank you for the feedback, we’ll edit the picture.

    Filip M - Official Prusa CS -

    I was informed by support (when I had issues with the PTFE tube) that it should be cut a little to 44.2mm. Should this be added?

    Mathieu - Reply

    Hello Mathieu, yes it is correct and it will be added.

    Martin L. - Official Prusa CS -

    My bag came with 2 M18s and 3 M20s. I used the spare parts bag to make up the difference.

    Rick Seiden - Reply

    My ptfe tube was already at 44.2 mm even though the bag said 45mm.

    Gary Minnick - Reply

  3. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Extruder-body (1x)

    • Adapter-printer (1x)

    • FS-lever (1x)

    • The list continues in the next step.

    The stl’s show: ‘adapter-printer-mmu2.stl’ (without ball hole) and ‘adapter-printer.stl’ (with ball hole). If the assembly includes MMU2 this step should note the use of the ‘adapter-printer-mmu2.stl’ (without ball hole).

    Jim - Reply

    Hi Jim, this assembly is dedicated to single material MK3S. Multi material upgrade will have separate manual.

    Jakub Dolezal -

    Yeah there is no other upgrade manual for the Mk3 MMU2 to the Mk3 MMU2s

    Kyle Smaagard - Reply

    Hi there, how about this one? Is it not the one you were looking for? Original Prusa i3 MK3S/MK2.5S & MK3/MK2.5 to MMU2S

    Martin L. - Official Prusa CS -

    I would like to use a brighter color (orange) for clarity. Which piece(s) should be black so that filament sensor will work?

    Thanks,

    Paul

    Paul Williams - Reply

    Hello Paul, the FS-lever has to be black, other parts can be made from PETG of another color.

    Martin L. - Official Prusa CS -

  4. For the following steps, please prepare:
    • For the following steps, please prepare:

    • M3x18 screw (1x)

    • M3x10 screw (1x)

    • M3nS nut (2x)

    • M3n nut (2x)

    • Steel ball (1x)

    • Magnet 10x6x2 (1x)

    • Magnet 20x6x2 (1x)

  5. Take two M3nS nuts and insert them in the Extruder-body. Make sure both are all the way in. Ensure correct alignment using the Allen key.
    • Take two M3nS nuts and insert them in the Extruder-body. Make sure both are all the way in.

    • Ensure correct alignment using the Allen key.

    • Secure the nut using an M3x10 screw. Tighten the screw just slightly, later on we need to add the P.I.N.D.A. sensor.

    • Take two M3n nuts and insert them in.

    • Use the screw pulling technique.

    • Take the smaller magnet (10x6x2) and insert it carefully in the FS-lever. Majority of the magnet will be hidden inside the printed part.

    The self printed STL for the extruder body have the PINDA sensor bracket gap connected with a small layer of plastic. I think this is supposed to be cut off but I don’t think I saw any mention of this. The picture above shows the part with the gap.

    The first time I did this I didn’t think too much of it and the plastic near the screw cracked while tightening the M3x10 screw without applying much force at all. Luckily I had skipped ahead and hadn’t taken apart the old extruder yet so I re-printed the part. Once I cut off the small layer of plastic things worked ok.

    A Rosso - Reply

    Thanks for the info, I printed the parts myself as well and I also have the connection on the first layer. I cut it so I won’t have the same problem you had. Thanks again! :)

    Should be added to the manual.

    Guntor H -

    Make sure that the upper (not PINDA) M3nS is inserted deep enough or you will get a problem in step 42.

    Ulrich Homann - Reply

    I second this comment.

    Double check the M3nS placement or you will be very sad in 3 hours (Step 42) when you have to disassemble the entire extruder because the hole is off. If you don’t believe us, read the comments in step 42 =)

    Barry Hulce -

    Using screw pulling technique has rounded one of my holes. I still haven’t figured what to do with it now. So be careful!

    Tonny - Reply

    Exactly the same happened to me when pulling the nut into place. Couldn’t’ undo the screw and the nut started spinning leaving me stuck. In the end I needed to get a replacement part - I’m not sure these holes are strong enough for any degree of tightening (my parts were Prusa printed - not home printed)

    Chris - Reply

    I had the same problem when pulling the nut into place. I first didn’t hold the nut in place, so it rounded the hole and I could throw away the part and reprint it. Luckily I have a spare printer - maybe an idea to put as much of the assembly of the new parts before taking apart the printer for people who aren’t so lucky. This time I held the nut in place with some pliers until the very last moment - this worked.

    I also had a lot of issues getting the magnet to fit. I ended up heating up a small flathead screwdriver with a lighter and squaring out the hole. This worked. Oh, the joy of printing with a 0.6mm nozzle.

    Sijmen Schoon - Reply

    I’ve had the screw pulling method brick parts in the past. The problem appears that microscopic strands of filament get pushed into the threading of the nut, then when the nut is pulled into place the friction of the nut/screw combo creates heat enough to melt the filament. The melted filament then cools and fuses the nut and screw together.

    When this happens it’s impossible to remove the screw or nut without destroying either, or worse the plastic part. Additionally when this happens Pursa support plays dumb and refuses to help.

    Recommended solution:

    1. thread the nut onto a screw,

    2. use the screw as a handle to help guide the nut into it’s recessed hole.

    3. once the nut is pressed into it’s hole, then remove the screw.

    Ro.Yo.Mi - Reply

    Hello Ro.yo.mi,

    That is an interesting theory. Do you believe that the friction of the nut/screw creates heat over 200°C , which is the melting temperature of PETG? And even given the benefit of doubt, do you believe that melted PETG fuses metal?

    That being said, your twist on the Screw pulling technique is valid. The only difference is that you suggest inserting the nuts crewed on a screw and we suggest insert the nut and then screw it from the other side.

    Martin L. - Official Prusa CS -

    I can’t see that what you’ve said is correct. Most problems with striping the hole will come from not aligning the nut with the hex shape of the hole, when pulling it in.

    David Moore -

    I also broke the nut trap free due to extra friction from a strand of filament (you can see the threaded filament on the threads when you finally free it which was i also agree….very difficult without damaging the part) I do not think it melts at 200C but it certainly gets caught in the threads creating more friction resulting in the nut traps failing. Nut traps sub optimal for parts that need significant torque, if you want to take your build to a higher professional quality I would highly recommend M3 threaded heat inserts and insert them with a soldering iron. Nut traps are a cheap work around and you can see and feel this during a kit assembly / upgrade (falling out or failing nut traps). Using heat insert not only makes the build more fun and challenging it also adds a more professional finish to the printer. Including this as an alternative for your kit would cost only cents and you wouldn’t even need to change the parts and would give users the option to skip this headache and improve quality of build

    Charles S. - Reply

    Ro.Yo.Mi is right and this is a well known problem in engineering; what appears to be a light pressure and motion together cause extremely high point contact temperatures, a process used in friction welding, that will dissipate quickly afterwards but the damage is already done. It is common to apply a very light smear of oil to the threads if you adopt the pull through technique to avoid the issue.

    Mike - Reply

    In extruder parts assembly picture, the M3nS nut (2x) are shown as dark blue , should be light blue.

    The Pinda retaining M3x10 screw (1x) is shown as purple, should be dark blue.

    peter - Reply

    Hello Peter,

    Could you show us a screenshot off what it looks like on your end? There is no need for PINDA M3x10 screw to be shown as dark blue, it is marked purple in the assembly step as well as in the picture. Same goes for M3nS nuts with blue.

    Marcin M. - Official Prusa CS -

    THIS IS A DESIGN FLAW!

    I set my nuts very carefully using a flat surface and pressure to get them started straight. The first one pulled in without incident. The second one stuck to the screw and rotated just as others have reported. I didn’t want to wait for a new part so I extracted the nut-and screw as follows:

    I installed a thin cut-off wheel in my Dremel rotary tool and carefully cut the head off the screw. To avoid melting the plastic, I would apply the grinder to the head for no more than two or three seconds. I would then apply water to the head with a small flux brush. I repeated this until I had cut off the head. There was approximately a half millimeter of head remaining on the shaft. I ground this down using the same procedure. Then I knocked the shaft and nut out of the hole with a thin punch.

    I pressed in the replacement nut with a bigger punch to avoid a repeat of the problem. I suggest that all nuts be installed in this manner or with a press until Prusa determines a final fix.

    Keith Selbo - Reply

    I inserted screw into a washer, then hole. Start threading the nut, align then tighten the nut. I had no problems using this method, described by Joseph.

    Mark Tellier - Reply

  6. Insert the FS-lever in the body. Secure the part with a M3x18. Tighten it, but ensure the lever can move freely.
    • Insert the FS-lever in the body.

    • Secure the part with a M3x18. Tighten it, but ensure the lever can move freely.

    • WARNING: make sure the following procedure is done right, otherwise the filament sensor won't work!!!

    • Insert the bigger magnet (20x6x2) in the Extruder-body, it will stick out:

    • Correct setup: magnets are repelling each other, thus the lever is pushed to the right.

    • Incorrect setup: magnets are attracting each other, thus the lever is pulled to the left.

    Be aware the magnets really want tom jump out!

    Dean Kinton - Reply

    I think the little switch piece should be designed to insert the magnet from the other side so it can not jump out. I ended up putting a bit of superglue on it to stop the jumping.

    Russell McCampbell - Reply

    Note that the lever will actually need to move really freely, else it won’t properly return to its home position when there’s no filament.

    Sijmen Schoon - Reply

    I wrapped the magnets in scotch tape to prevent them flying out of there sockets.

    Paul Saba - Reply

    +1 Paulo Saba work like a charm

    Edgar Munhoz -

    Thanks Paul, now i will only have one small magnet to search for under my desk.

    Paul Kingwell -

    Thank you Paul Saba. The scotch tape gives them enough friction to stay in place, but leaves them “removable” if needed

    Jay Sinnett - Reply

    +1 Paul Saba

    Jim Wade - Reply

    I put some masking tape around the magnets to keep them snug in the sockets. This worked really well.

    Chris - Reply

    That did the trick indeed! Thanks Chris.

    Charles Buddendorf -

    The M3x18 screw SHOULD NOT extend beyond the bottom of the body. If it does, it will interfere with a step much later in these instructions.

    Brien - Reply

    That’s correct. Also, if it does, you have brutally overtightened the lever.

    Martin L. - Official Prusa CS -

    It looks like the longer magnet should not poke all the way through its slot. There’s a plastic window that keeps it from sliding too far. It looked like my long magnet stuck out farther than shown in the photo. I found the plastic part that will close over this assembly, from Step 8, and checked that it seats correctly.

    Gary Boone - Reply

  7. Take the printed part Adapter-printer and insert the steel ball. Roll with the ball to all sides to ensure smooth movement.
    • Take the printed part Adapter-printer and insert the steel ball.

    • Roll with the ball to all sides to ensure smooth movement.

    • In case of any rough surface, remove the ball and clean the inside of the printed part.

    • Place the printed part together with the steel ball in the Extruder-body. The surfaces of both parts should be almost aligned.

    • DON'T use any screw to secure the Adapter-printer. It should hold inside the Extruder-body by itself.

    The stl’s show: ‘adapter-printer-mmu2.stl’ (without ball hole) and ‘adapter-printer.stl’ (with ball hole). If the assembly includes MMU2 this step should note the use of the ‘adapter-printer-mmu2.stl’ (without ball hole).

    Jim - Reply

    As mentioned in step 3 by @jakoob, these instructions are not for the MMU2S upgrade, only the MK3S without MMU2. The MMU2S instructions are being worked on.

    Chris Elliott -

    In English usage, the word ‘in’ is dropped from the end of the sentence, as follows:

    Take the printed part Adapter-printer and insert the steel ball.

    “Place the printer part together with the steel …” should be replaced with “Place the printed part together with the steel …”

    Sorry, can’t help myself ;-).

    Frank

    Frank Paynter - Reply

    Hi Frank, no worries, I'm grateful for the feedback ;)

    Jakub Dolezal -

  8. For the following steps, please prepare: Extruder motor (1x)
    • For the following steps, please prepare:

    • Extruder motor (1x)

    • Extruder-motor-plate (1x)

    • M3x10 screw (2x)

    • ATTENTION: there is a set of the Bondtech gears. Make sure you have all the parts and you are using correct ones.

    • Use now: Bondtech gear with a lock screw. If the screw is out, gently screw it in (leave space inside for the shaft).

    • Use later: Bondtech without a lock screw, bearings and a shaft. Keep the bearings somewhere safe, they tend to roll away ;)

    Find those roller bearings on the floor that you dropped before…

    Doug Johnson - Reply

    I left my shaft/bearings/Bondtech gear assembled on the old part so the bearings wouldn’t be tempted to misbehave ;-)

    Frank Paynter - Reply

    You dont need to prepare the bontech without lock screw in this step, it comes later (step 27). This prevents uneccesary rolling away

    Tor Andre - Reply

  9. Take the Extruder-motor-plate and secure it using two M3x10 screws. Use the cable as a guide to properly orient the part. Resist the temptation to place a screw in the third hole! Leave it for later ;)
    • Take the Extruder-motor-plate and secure it using two M3x10 screws. Use the cable as a guide to properly orient the part.

    • Resist the temptation to place a screw in the third hole! Leave it for later ;)

    • Rotate the shaft as in the picture. Flat part must in the direction of the arrow.

    • Slide the gear on the shaft, the lock screw must be facing against the flat part of the shaft. Tighten the screw slightly.

    • There is a "channel" for the filament inside the printed part. Align approximately the teeth on the gear with it.

    • Don't tighten the screw just yet. We will align it properly first. See the next step.

    Flat part must in the direction of the arrow. —> Flat part must be facing in the direction of the arrow.

    Thomas Gelsdorf - Reply

  10. Take a piece of the 1.75 filament. You can use the bundled one on a spool, don't use the black nylon, which is too thick. Straighten the filament as much as possible. Place the filament along the path and align the gear properly. The filament will be always slightly bent. Use it anyway for the initial alignment.
    • Take a piece of the 1.75 filament. You can use the bundled one on a spool, don't use the black nylon, which is too thick. Straighten the filament as much as possible.

    • Place the filament along the path and align the gear properly.

    • The filament will be always slightly bent. Use it anyway for the initial alignment.

    • For a final check replace the filament with an Allen key. Bear in mind, the key has slightly different size than the filament.

    • Tighten the screw slightly to temporarily fix it, we will make the final check and tightening later on. Be careful, you can strip the thread.

    • Don't use any glue to fix the screw in place, you won't be able to release it, in such case you might have to replace the entire motor.

    I’ve had issues with the grub screw coming loose in the past, and you’re right — glue/loctite is no good here. For little stuff like this, I like to use a little piece of waxed dental floss. It can be finicky to get it in there, but it gives just enough friction to hold, but not enough to make it impossible to take out again. The excess can be burnt off with a lighter

    Lars Jacobsen - Reply

    bondtech recommends loctite thread locker (blue 242) to be used on their gear, please update manual to state this. without it, many users WILL have issues due to the 2x3mm grub screw backing out from vibrations. this is the only reason i have had failures and spaghetti blob failures.

    page 8: https://www.bondtech.se/wp-content/uploa...

    Andreas Stevens - Reply

    Hello Andreas, it’s not necessary to use that glue.

    You risk stripping the screw if you don’t apply it properly - it might be harder to remove the screw without proper preparation.

    Filip M - Official Prusa CS -

    The allen key doesn’t fit, so that doesn’t work…. using some straightened filament is best. Also the channel on one side is deeper than the other….I worked with the smaller shallower one.

    David Moore - Reply

    The channel on the right side is lower than the left to accommodate the PTFE tube, I found it more accurate to temporarily lay the extruder in place to align the filament path more accurately

    Clive Bradshaw - Reply

    I had problems with this grub screw coming loose and I agree with Andreas Stevens about using Loctite 242. I used it on my original MK3 kit (after having it work loose) and I could remove the grub screw OK when I installed the MK3S upgrade. The secret is that Loctite 242 is heat sensitive and to break the bond just put hold a small soldering iron onto the screw and the heat will break down the glue making loosening the screw easy. Using nothing is not an option as the only print failure I have had so far (and I have printed 100’s) is when the grub screw worked loose early on. I apply the Loctite by putting a small drop onto the end of a screwdriver and letting it run into the thread with the screw loose then wipe off any excess.

    Hans Heck - Reply

    If I stripped the grub screw, I have to get a replacement? It seems secure but the screw might be stripped……

    Travis Crusenberry - Reply

    Hi Travis, there should be a spare grub screw if you purchased a kit.

    If the gear is properly aligned then you can still use it, even if the screw is stripped, but it’s best to replace it.

    Filip M - Official Prusa CS -

  11. For this step, please prepare: Extruder-cover (1x)
    • For this step, please prepare:

    • Extruder-cover (1x)

    • M3nS nut (1x)

    • Slide the nut all the way in.

    • Ensure correct alignment using the Allen key.

    • Leave the second slot empty, we will use it later.

  12. For the following steps, please prepare: Hotend for MK3S (1x)
    • For the following steps, please prepare:

    • Hotend for MK3S (1x)

    • M3x40 screw (3x)

    • M3x10 screw (2x)

    • We will use some screws later, so keep them around.

    • Your MK3 hotend might have a green dot or no dot at all, it is ok.

    … and what’s the meaning of the yellow dot in the picture?

    Thomas Gelsdorf - Reply

    The yellow dot on the extruder? That does not mean anything in terms of assembly but is an indicator of what model/date the extruder was made for reference in future upgrades. I believe the yellow dot just means MK3S, or from the time of the MK3S.

    Mathieu -

    It means the hotend is for MK3S - it comes with a shorter PTFE tube. It might not be used in the future, where we fully switch to shorter tubes. It’s a mark for “transition” period.

    Filip M - Official Prusa CS -

    I did not receive an MK3S hot end and assume I use the MK3 with the shorter PTFE tube.

    August Binkert - Reply

    Hello August,

    The only difference between both hotends is the length of the PTFE tube. If yours is 44.2-3mm, then you have the S version.

    Marcin M. - Official Prusa CS -

  13. Take two M3x10 screws and insert them in the holes. Doing this now makes the assembly slightly easier, but both holes are shallow and the screws might fall out. If this happens, you can continue without them and put them back later on (you will be notified). Also note, that in few upcoming pictures the screws will be missing. Hotend assembly was completely reworked from MK3 to avoid bad placement. Also any future maintenance is much easier. Place the hotend next to the Extruder-body, see the grooves in the printed part, which are in the shape of the hotend.
    • Take two M3x10 screws and insert them in the holes. Doing this now makes the assembly slightly easier, but both holes are shallow and the screws might fall out. If this happens, you can continue without them and put them back later on (you will be notified). Also note, that in few upcoming pictures the screws will be missing.

    • Hotend assembly was completely reworked from MK3 to avoid bad placement. Also any future maintenance is much easier.

    • Place the hotend next to the Extruder-body, see the grooves in the printed part, which are in the shape of the hotend.

    • Correctly placed hotend. Cables should point in the direction behind the hand, we will align them in the next step.

    Correct the photos - 1st photo and steps tell you to add M3x10 screws however the next two photos are shown without the screws.

    Paul Thomas - Reply

    Hey Paul, thanks for the feedback. Screws were removed only to take pictures, they should be left in there.

    Filip M - Official Prusa CS -

    The written instruction makes the cable placement clear, but confidence would be higher if the hand in the photo did not conceal the alignment of the cables.

    Rob McCoy - Reply

    I thought the same thing. The photo in the next step does clarify this step.

    Ro.Yo.Mi -

    These screws are the worst. Is there a reason these aren’t coming from the back?

    Daniel Wilday - Reply

    Hi Daniel, our developers have concluded it’s the best way to mount those.

    Filip M - Official Prusa CS -

  14. In order to protect the hotend cables and ensure proper orientation, it is highly recommended to use a box. Use the one provided in the kit. Place the Extruder-body with the hotend on the box and make sure the cables are pointing down. Place your finger temporarily on the longer magnet  and place the extruder motor assembly on the Extruder-body. The Bondtech gear might pull the magnet out while assembling parts together.
    • In order to protect the hotend cables and ensure proper orientation, it is highly recommended to use a box. Use the one provided in the kit.

    • Place the Extruder-body with the hotend on the box and make sure the cables are pointing down.

    • Place your finger temporarily on the longer magnet and place the extruder motor assembly on the Extruder-body. The Bondtech gear might pull the magnet out while assembling parts together.

    • Make sure both parts are aligned.

    • Place the Extruder-cover on the Extruder-body. Again, make sure parts are properly aligned.

    • Insert two M3x40 screws, you've prepared earlier. Tighten them, but be careful, they are slightly longer, than the thickness of the entire assembly. Keep the third screw, we will use it later.

    • Place the extruder aside for few steps, we need to prepare another part. Leave it on the box to prevent damaging the cables.

    in this step, my ptfe tube in the hotend is deformed slightly by the bondtech gear. is this expected?

    adcurtin - Reply

    Mine just touches the gear but is not deformed. I would assume that that would not be proper since it would interfere with the filament feeding through.

    Paul Thomas -

    My PTFE tube also touches the gear, but I continued anyway. Now that it is all done I keep hearing a “grindy” noise every time the filament retracts during printing and I’m guessing it is because of this. I presume (if this is indeed the cause of the noise) the PTF will eventually wear down to the point it wont “grind” anymore? Any suggestions?

    Luis Vallecillo -

    Hey guys,

    Please check the length of your PTFE tube - it should be 45mm. If it’s barely touching the gear, then it should be OK. Please contact support if it’s grinding too much.

    Filip M - Official Prusa CS -

    one of mine was 45.5, the other was 45.25. Both are deformed by the bondtech gear. I’m probably going to try to trim the shorter one up without losing too much of the flange.

    Nathan Cerny -

    What does this mean “Tighten them, but be careful, they are slightly longer, than the thickness of the entire assembly.” Does this mean the screws should not protrude out regardless if not tight? or Seat the screws until they are tight regardless if they stick out a bit?

    Paul Thomas - Reply

    Hey Paul,

    It means they will protrude a bit.

    Filip M - Official Prusa CS -

    I have just got to this stage and both included new PTFE tubes come in contact with the gear on the stepper motor. I have removed them and tried to re-insert them but they still sit too high. I will be contacting customer support.

    Stephen Vasey - Reply

    Why did we have to prepare 3 x M3x40 screws , when only 2 was needed?

    Per Mejdal Rasmussen - Reply

    What happened to the third screw from step 12? Why it was prepared but never used?

    Tonny - Reply

    Hello Tony,

    It is used later in Step 22 when securing the IR sensor.

    Marcin M. - Official Prusa CS -

    My PTFE tube is also just touching the gear. Should it be cut back a little bit or not? I left it as-is and am having trouble printing first layers, not sure if it has to do with this or not. Need some feedback on this and/or support needs to address it. Thank you.

    Nelson - Reply

    Hi,

    If the tube is too long, then you can always trim it or contact our support for replacement. It shouldn’t affect the first layer at all.

    Filip M - Official Prusa CS -

    I ordered spare PTFE tubes with my upgrade and so ended up with a Mk3-spec PTFE tube, not realizing the difference - it went way up onto the gear, ‘cos it’s like 50mm long… only then did I notice another bag that had TWO 45mm tubes. Whoops! I can understand the mixup but hopefully you didn’t sent out too many mk3 replacements along with mk3s upgrade kits…

    Ben Scott - Reply

    Hello Ben,

    If you still have those 50mm PTFE tubes, you can still turn them to MK3S spec, please see our guide on how to do it here:

    How to trim PTFE tube - Original Prusa i3 printers

    Marcin M. - Official Prusa CS -

    One of the hex nuts in the extruder body is spinning and I am unable to get it out or remove/tighten the screw, any tips on how to fix it?

    Dave Nelson - Reply

    Hello Dave,

    You could do partial disassembly to access the nut and try to put a small amount of glue to keep it in place , cyanoacrylate glue should do fine.

    Marcin M. - Official Prusa CS -

    Well, the assembly won’t fit on a box if the two not-shown M3x10 screws are actually in place. Maybe the suggestion is to push the screws into the cardboard? It’s simple enough to assemble without a box and with the screws sticking out. The screws are shown again in Step 18 and used in Step 19

    Gary Boone - Reply

    Hello Gary, it doesn’t have to lay entirely flat if you installed those 2 screws earlier on.

    Filip M - Official Prusa CS -

  15. For the following steps, please prepare: X-carriage (1x)
    • For the following steps, please prepare:

    • X-carriage (1x)

    • M3n nut (2x)

    • M3nS nut (4x)

    • IR-sensor cable (1x)

  16. For the following nut insertion USE A SCREW. THAT'S AN ORDER!!! Seriously, use a screw to pull the nuts in, both have to be properly seated in the X-carriage. Take both M3n nuts and using pliers (or screw) push them in the X-carriage, then using a screw from the other side, pull them all the way in.
    • For the following nut insertion USE A SCREW. THAT'S AN ORDER!!! Seriously, use a screw to pull the nuts in, both have to be properly seated in the X-carriage.

    • Take both M3n nuts and using pliers (or screw) push them in the X-carriage, then using a screw from the other side, pull them all the way in.

    • Don't forget to remove the screw.

    • Take all four M3nS nuts and insert them in. Ensure correct alignment using the Allen key.

    • From now on, keep in mind the nuts are inside, avoid rotating the X-carriage "downwards", or the nuts might fall out.

    Step no 17 forces you to turn the piece over. Maybe reverse the order,

    although in fact the nuts seemed snug enough not to fall out

    Henry Casson - Reply

    add a touch of superglue to the center nut. Send me gummy bears later as thanks :)

    Russell McCampbell - Reply

    Hello Russell,

    You can use a dab of glue if you have issues with locking nuts in place, however be extra careful to wait until it fully sets in so that screws don’t get locked permanently, as you may have difficulty with reassembly later, should you ever need to do any troubleshooting/reassembly.

    Marcin M. - Official Prusa CS -

    Or use blue (removable) locktite on all metal to metal connections most important for the bondtech driver gib

    Mustrum Ridcully - Reply

    Considering that item need to be held in the air all the time nut are constantly falling off. So either add them in later when needed or maybe use some M3x10 nuts or something to keep them in place.

    Tonny - Reply

    If your square nuts fit snugly in this step, sure add them in. If not, they will constantly be falling out for many steps to come, eliciting much profanity. You really only need to add them in before you zip-tie the x carriage in step 44. The two top square nuts (the bottom two in your picture ) were the two that caused me the most trouble. They aren’t needed until step 61 and are still easily accessible then.

    cmore11 - Reply

    If you stick a small piece of blue masking tape to any square nuts that are loose it will hold them in place without interfering with the threads

    ahill22600@gmail.com - Reply

    Can’t see why you add the square nuts here, they can easily be inserted after you mount the extruder to the x axis.

    Mister Glass - Reply

    It’s easy to forget about them even when it’s mentioned again during the assembly. That’s why we recommend to insert them a bit earlier.

    Filip M - Official Prusa CS -

    Am I the only one who cannot push the M3n nuts in place. I tried pulling in with a screw as recommended but the tolerance of the 3d printed hex recesses is too bad. I tried using a drill press to press them in place but that didn’t work either. This design seems like something a grad student would come with not a design engineer. Why print parts for mass production when you can injection mold more efficiently at a fraction of the cost and with significantly better tolerance. I am beginning to think the long lead times for shipping is due to Prusa’s inefficient design, manufacturing, and assembly process. Apologies for the frustration but this should be a very straightforward assembly. For crying out loud we are just screwing parts together not doing brain surgery.

    Darryl DLima - Reply

    Hi Darryl, you can always check the holes for debris or to check if there’s too much material - if needed you can remove some material with an exacto knife. Plastic parts will never be perfect, but I can assure you the tolerances are enough to insert a nut. Perhaps you deformed the hole a bit when inserting the nut for the first time - a knife will always help in situations like this.

    Filip M - Official Prusa CS -

    I had some trouble getting that square nut in above the rounded surface. Put it on the end of a screw as a handle then a little pinch with needle nose pliers got it in there no problem, take the screw out and pinch again.

    svachalek@gmail.com - Reply

    Used glue stick to hold nut in… worked ok.

    GARY K FAIN - Reply

    I have to agree with Darryl. One M3n went in fairly easily. I had to lightly tap on the other one with a tack hammer to nudge it in a bit at a time. No debris in the hole. It was a super tight fit.

    Brenda Bell - Reply

  17. Take the IR-sensor cable and locate the end with the smaller connector. Place cable in the X-carriage, use the small printed overhangs to keep the cable inside.
    • Take the IR-sensor cable and locate the end with the smaller connector.

    • Place cable in the X-carriage, use the small printed overhangs to keep the cable inside.

    • The distance between the connector and the X-carriage should be around 15 mm (0.6 inch). We will adjust it later.

    • Guide the cable through the slot, remember this path, we will use it for other cables as well.

  18. Following cable management is CRUCIAL for the extruder TO WORK PROPERLY! Read the instructions carefully.
    • Following cable management is CRUCIAL for the extruder TO WORK PROPERLY! Read the instructions carefully.

    • Start by making a small loop just below the extruder motor. Leave a slack about 2-3 cm (0.8 - 1.6 inch) This is comes handy for easier disassembly in the future.

    • Then guide the cable in the "channel" all the way to the back.

    • Slightly bend the cable down to form it around the edge.

    • Also, prepare X-carriage, both M3x10 screws (if you haven't used them already) and the longest Allen key with the ball-end, you will need it.

    If, like me, you are annoyed that the cable won’t stay in the channel: at step 25 the fan and fan cable will ensure that the motor cable stays in place.

    Bas - Reply

  19. Following cable management is CRUCIAL for the extruder TO WORK PROPERLY! Read the instructions carefully. Before you assemble the X-carriage, check the nuts in the Extruder body are still in place. The upper nut sometimes falls out. Grab the X-carriage and place it onto the back of the extruder assembly as shown in the picture.
    • Following cable management is CRUCIAL for the extruder TO WORK PROPERLY! Read the instructions carefully.

    • Before you assemble the X-carriage, check the nuts in the Extruder body are still in place. The upper nut sometimes falls out.

    • Grab the X-carriage and place it onto the back of the extruder assembly as shown in the picture.

    • Make sure the motor cable follows the channel both in Extruder-body and X-carriage. In the X-carriage the motor cable will follow the path of the IR-sensor cable.

    • ENSURE NO WIRE IS PINCHED! Then use the M3x10 screw and Allen key with ball end to connect both parts together. If you are inserting the screw at this moment, it will be slightly inclined in the beginning, but it will "straighten up" after few turns. Don't tighten the screw completely, we need to adjust the IR-sensor cable.

    • Turn the extruder to the other side and if needed insert the second M3x10 screw. Don't tighten the screw, we need to adjust the IR-sensor cable.

    missing the bag o’ gummy bears.

    this step felt a little complicated, needed a third hand ; )

    Byron Wingerd - Reply

    i haven’t gummy bear :..(. I have got free update with no gummy bear.

    Fabio Giuseppe Barbalace - Reply

    Hey Fabio, Haribos only come with full kits or printers :)

    Filip M - Official Prusa CS -

    Gummy bears were not included in the upgrade kit :(

    Tonny - Reply

    I’m sad that upgrades don’t warrant gummy bears…

    John Radich - Reply

    I would place 2 nuts inside instead of 2 screws… this is much to difficult to tighten them… it could be easily done from the other side

    Chris Boer - Reply

    Easily the most difficult and annoying part. Can’t tighten the bolt because of the angle. No gummy bears either with the upgrade kit!

    Morvar - Reply

    Hello Morvar, Use the needle-nose pliers to place the screws straight. Then you can tighten them with the Allen key even when the key will be at an angle.

    Martin L. - Official Prusa CS -

    My extruder motor wire would not stay in place. It kept coming out. And getting everything lined up was a real hassle. Then screwing down the M10s without an allen wrench with a ball on the end was nearly impossible. This step was very difficult.

    Rick Seiden - Reply

    “Grab the X-carriage and place it from the back of the extruder” —> “Grab the X-carriage and place it onto the back of the extruder assembly as shown

    Frank Paynter - Reply

    How in the world this was accepted as a good design, it is patently obvious that the m10 screws should have a nut inside the shroud and the head outside. Come on Prusa did you even try.

    Caleb - Reply

    if you use the allen key with the ball it’s not a problem.

    Brian Whittle -

    the holes for the top square nuts need to be slightly smaller so the nuts don’t fall out so easily

    Brian Whittle - Reply

    Hello , thanks for the comment, we’ll check the tolerances.

    Martin L. - Official Prusa CS -

    Caleb and Brian are right. Workarounds are poor excuses for a poor design. At almost every step of this assembly there is room for improvement, not to mention the inefficiency of using 3d printed parts with poor tolerance and finish for a mass produced product. Even when I print parts for myself, I am constantly checking and adjusting tolerances during assembly.

    Darryl DLima - Reply

    2.5mm ball-head screw driver — not allen key — makes this step a piece of cake.

    Brenda Bell - Reply

    This step was impossible for us as written, so I pulled everything (hotend, motor) back out and with nothing in the way attached the X Axis body to the extruder body - this step, but with only the plastic parts. Then we followed all the steps adding the hotend and motor and cover back on. Worked fine - you can stuff the cables where they need to be after everything is connected, so I’m not sure the advantage of the order in the directions as written. If I build another one, I’ll certainly attach the two plastic parts first - just remember the IR sensor cable needs to be sandwiched between them in the channel.

    Gregg Carrier - Reply

  20. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Prusa IR-sensor (1x)

    • M2x8 screw (1x)

    • BE CAREFUL with the filament sensor, do not touch the black PCB nor the chips on it. Hold the PCB from sides.

  21. Place the IR-sensor on the top of the  Extruder-body and secure it with the M2x8. Make sure the black plastic "u-shaped" part is facing down. Tighten the M2x8 screw, the sensor shouldn't be able to move, but be careful the PCB isn't indestructible ;) Connect the cable, mind the correct orientation of the connector and wires.
    • Place the IR-sensor on the top of the Extruder-body and secure it with the M2x8. Make sure the black plastic "u-shaped" part is facing down.

    • Tighten the M2x8 screw, the sensor shouldn't be able to move, but be careful the PCB isn't indestructible ;)

    • Connect the cable, mind the correct orientation of the connector and wires.

    • Leave a slack behind the sensor like in the picture. Don't create too big loop as it might interfere with the frame. If needed adjust the length by gently pulling/pushing the cable.

    • Ready? Ok, check once more no cable is pinched and tighten both M3x10 screws installed previously.

    This screw strips very easily. Be careful!

    Joe P - Reply

    Yes, the screw is not really 1.5mm, therefore the allen key does not fit, and it strips. used both screws. both striped, will have to just glue the part in…

    David Moore -

    I resorted to using pliers to turn the screw, because it was impossible with a 1.5mm key.

    Bas -

    It is possible, if you are dumb enough, to put it in upside down, with the bulkier components upward. You will discover this when yo try to put the cover on, sometime in the future

    Henry Casson - Reply

    1. My IR-sensor does not have a "black plastic u-shaped part”

    2. It appears the headers on my IR-sensor were soldered to the opposite side.

    3. Even if 1&2 were not an issue, the part would still not fit flush into the rectangular cutout. It is too wide.

    Jason Pippin - Reply

    UPDATE - My kit had the wrong sensor shipped. Receiving a replacement. +1 to PRUSA chat support.

    Jason Pippin -

  22. Finish the sensor assembly by inserting an M3x40 screw.
    • Finish the sensor assembly by inserting an M3x40 screw.

    • Make sure all the gaps are gone.

  23. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Hotend fan Noctua (1x)

    • M3x14 screw (3x)

    • Make sure you are using the correct screws.

    Only 1 M3 x 14 in my bag, had to use 2 from spares bag.

    peter - Reply

    I was also missing an M3x14 and had to use a spare.

    Brenda Bell - Reply

  24. Before you move to the next step, take an Allen key and GENTLY PUSH the motor cable to the channel to create space for the fan cable.
    • Before you move to the next step, take an Allen key and GENTLY PUSH the motor cable to the channel to create space for the fan cable.

  25. The fan has two sides, one has a Noctua sticker. Make sure, this side is facing inside the extruder. First, create a loop on the cable. Make sure the black protective wrap is close to the edge of the fan. See the picture. Place the fan on the extruder and proceed in the following way:
    • The fan has two sides, one has a Noctua sticker. Make sure, this side is facing inside the extruder.

    • First, create a loop on the cable. Make sure the black protective wrap is close to the edge of the fan. See the picture.

    • Place the fan on the extruder and proceed in the following way:

    • Start by placing the fan's cable in the upper channel

    • Slide the fan close to the X-carriage and GENTLY PUSH the cable in using an Allen key. Before you push the fan all the way to the left, place the cable in the X-carriage channel.

    • FINAL CHECK! The fan is oriented with the cable facing up, then the cable goes through the upper channel all the way to the X-carriage. In the X-carriage don't forget to use both channels. Make sure the CABLE ISN'T PINCHED along the way!

  26. Use the three M3x14 screws to fix the fan in place. Don't over tighten them, you can break the fan's plastic casing. Also make sure the fan can rotate freely.
    • Use the three M3x14 screws to fix the fan in place. Don't over tighten them, you can break the fan's plastic casing. Also make sure the fan can rotate freely.

    • Note that the screws are "self-tapping" in the printed parts. There are no nuts.

    • Leave the last hole empty, for now.

    Do the three screws have nuts to attach to?

    Leon Bogaert - Reply

    Hey Leon, there are no nuts for those screws.

    Filip M - Official Prusa CS -

    Thanks! I thought I maybe skipped a step somewhere.

    Leon Bogaert - Reply

    I was not able to tighten left bottom screw all the way. Using nuts might be an improvement

    Tonny - Reply

    Hey Tony, it’s not necessary to have all of them fully tightened.

    Filip M - Official Prusa CS -

    When does the last screw gets in (last step)? At step 38 it looks already on place. What am I missing?

    Alex Emelianov - Reply

    Hello Alex, see the step 36, purple bullet-point.

    Martin L. - Official Prusa CS -

  27. For the following steps, please prepare: Extruder-idler (1x)
    • For the following steps, please prepare:

    • Extruder-idler (1x)

    • Bondtech WITHOUT the hole for the lock screw (1x)

    • Bearing (2x) might be stuck inside the gear

    • Shaft (1x)

    • M3n nut (1x)

    • M3x40 screw (2x)

    • Idler spring (1x) place the spring on the screw

    When pushing the shaft through the extruder-idler, be very careful. I broke 2 extruder-idlers because the placement hole is very tight. I would recommend printing more than one of these parts before the build to ensure you have a backup just in case.

    Dan H - Reply

  28. Insert both bearings in the pulley. Be aware that bearings can slip out during assembly.
    • Insert both bearings in the pulley. Be aware that bearings can slip out during assembly.

  29. Take M3n nut and place it in the Extruder-idler. Use the screw pulling technique. Insert the pulley in idler as shown in the picture.
    • Take M3n nut and place it in the Extruder-idler.

    • Use the screw pulling technique.

    • Insert the pulley in idler as shown in the picture.

    • Slide the shaft through the idler and pulley. Use reasonable force or you will BREAK the printed part.

    • Place your finger on the bearing and ensure it can rotate freely.

    Although the hex nut can go easily into its designated area, the shaft is a different story. As on the regular MK3, it is understandable that there is supposed to be a lot of resistance so that it doesn’t fall out, but the tolerance is just insanely small! I have to get a new one now…

    Mathieu - Reply

    I ended up reaming out the hole very slightly with an allen wrench to make the shaft insertion a bit easier. Still holds in there firm, but I didn’t feel like I was gonna snap the part in half

    Kevin Williams - Reply

    Hello Kevin,

    In rare cases there might be some extra material printed - we always recommend checking every printed part with holes and clean it, be it with an allen key or a hobby knife :)

    Marcin M. - Official Prusa CS -

    I heated up the shaft a bit with a lighter (make sure it burns fairly cleanly) and could push it right in. Watch your fingers though!

    Sijmen Schoon - Reply

    You can cleanup the holes with a 3mm (new) drill, driven by your fingers, after that it works fine, with a good fitting.

    Jan Vermond

    JanV - Reply

    That worked for me perfectly. Thanks for the tip!

    Guntor H -

    In the US, so I used an Imperial drill: 1/8” - which is a little too big (3.175mm). I used this only on one side. As expected, the shaft slides freely through the hole that I drilled out. So then I could push it against significant resistance into the hole on the other side. I supported the side with the small hole on the edge of my workbench so that there was no bending force on the plastic part, only compression.

    Jay Sinnett - Reply

    Gently hammering in the rod (you can use the back of a screwdriver in a pinch) worked really well for me

    fshstk - Reply

    I used the flat side (hinge area) of the pliers to push the rod into the part. this makes it a lot easier to gentry press the part in.

    parcival@gmail.com - Reply

    I used the M3x40 screw to clean the holes. Pushing it in and unscrewing it out if need be until it could be put in with some ease, using the teeth to clean up the part. Rod still took some force but not a lot, just push it (not hard) against the edge of a table and it went through pretty easy.

    sir.different@gmail.com - Reply

    Well, if you did not have a vise up till now, this would be a good time getting one. Very easy to apply linear and controlled force to the rod without the fear of cracking.

    Ok, fear was still there but you get yourself a vise, so that’s that :D

    Sam - Reply

    A small clamp like quick-grip by american tool makes it easy. If the clamp comes with rubber pads, remove the rubber pads and make sure you are centered on the metal pad. By clamping slowly and moving the gear to make sure it is aligned. It will “click” in and then you just finish clamping until it seats.

    dennis - Reply

    If you use a vice, this is relatively easy

    Tor Andre - Reply

    As suggested, I used a small metal C clamp and the shaft easily went into place. I finished up with a flat end center tap to push the shaft in a bit further.

    Mark Tellier - Reply

    I used a round modeling file to smooth and open the diameter of the hole. An adjustable pliers could be expanded enough to fit the just-inserted shaft and plastic part, allowing careful pressure to push the shaft through. You don’t have to worry about snapping the plastic mounts because the pulley prevents them from bending.

    After inserting the shaft, I found that it wasn’t centered. It was flush with the outside on one side and barely in the mount on the other side. The solution was to use a M3n nut and a bolt, screwing the nut on far enough to make about 2mm of the bolt emerge from the nut. Then that could be pressed against the shaft in the mount, pushing it in precisely 2mm, but no more.

    Gary Boone - Reply

  30. Let's use this opportunity to check once more the proper alignment of the filament and the Bondtech gear.
    • Let's use this opportunity to check once more the proper alignment of the filament and the Bondtech gear.

    • Push the filament from the top, through the Bondtech into the PTFE tube.

    • Check the alignment and if needed, adjust the position.

    • Tighten the screw, but be careful, you can easily strip it.

    • REMOVE the filament.

    In my assembly the PTFE tube slightly touches the Bondtech gear. Is this ok? I couldn’t push it further down.

    Dschey - Reply

    Hello Dschey,

    If it’s sitting slightly too high, you can try re-seating it. To do that, press the black collet clip and pull the PTFE tube tube out and then put it back in. If it’s sitting too high still, you can cut a bit of the tip off using a hobby knife, so it doesn’t reach the gears.

    Marcin M. - Official Prusa CS -

    Even though following the steps it is slightly too high. Ok, will cut it a little bit. Thanks from r 5e advice.

    Dschey - Reply

    I found that it was very difficult to push the filament into the PTFE tube due to an apparent misalignment - but in the direction we cannot control with the set screw: in the view above, the filament was too far out of the page to easily enter the PTFE tube. Should I just assume that the second Bondtech gear will provide sufficient pressure to compress the filament so it fits? There does not appear to be any way to adjust this position.

    Anne - Reply

    Hello Anne,

    The second bondtech should put enough tension to squeeze the filament in between both gears and correct the position, but only if the misalignment is very small. Double check if you haven’t put the motor bondtech gear the other way around.

    Marcin M. - Official Prusa CS -

    I have the same issue. The filament hits the inside of the PTFE tube but does not go in. Will check what it does after the second gear is installed.

    Frans Van maanen -

    I had the same issue. make sure you cut the filament at a 45 degree cut or greater. this will help it find its way.

    Kevin K -

    Use your fingernail to try and turn the bondtech gear. Mine fouled by a fraction of a mm and was very hard to turn, poor stepper motor!

    Rick - Reply

  31. Place the Extruder-idler in place and secure it using a M3x40 screw. Don't tighten the screw too firmly, it serves as a shaft for the idler. Check that the idler can rotate freely.
    • Place the Extruder-idler in place and secure it using a M3x40 screw.

    • Don't tighten the screw too firmly, it serves as a shaft for the idler. Check that the idler can rotate freely.

    Are the nylon washers from the original MK3 idler-mounting hinge no longer required?

    Richard Stone - Reply

    Hello Richard,

    That’s correct, no more washers :)

    Marcin M. - Official Prusa CS -

  32. Use the M3x40 screw with the spring to introduce tension to the Extruder-idler. Hold the Extruder-idler on the other side, until the screw reaches the nut.
    • Use the M3x40 screw with the spring to introduce tension to the Extruder-idler.

    • Hold the Extruder-idler on the other side, until the screw reaches the nut.

    • Since there is only one screw, you need to introduce a large force. The head of the screw, should be aligned or slightly below the surface.

    Is the tension set in that idler screw the same as it should be for printing? I have been having a couple issues with finding the right tension as it always leaves grinding marks.

    Mathieu - Reply

    Hey Mathieu, the gear will always leave some marks - it has to bite into the filament to move it.

    You could follow the method from that video (it’s for 2 screws, so you will need to add a few more turns in case of MK3S):

    https://www.youtube.com/watch?v=Lsa-PXAX...

    Filip M - Official Prusa CS -

    When I inserted this M3x40 screw with the spring, I did not have to exert any force at all. It reached the nut with no issues and I tightened it until the tip of the bolt was flush with the nut. I can push on the head of the bolt with my finger and feel it spring in and out. When I insert filament, the idler does pop out a little and I can’t push in as much on the bolt anymore - the spring is now working. But barely since there was no required force for the bolt when I screwed it in. Is this normal?

    Nelson - Reply

    Hi Nelson,

    It will be OK as long as the gears can grip the filament. If it’s slipping, then it means the idler is too loose.

    Filip M - Official Prusa CS -

  33. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Print-fan-support (1x)

    • M3x10 screw (1x)

    • M3n nut (1x)

  34. Take the M3n nut and insert it all the way to the support. It is crucial! Use the screw pulling technique.
    • Take the M3n nut and insert it all the way to the support. It is crucial!

    • Use the screw pulling technique.

    • Place the support on the extruder and ensure the inclined part is facing "down" (towards the nozzle).

    • Secure the support using an M3x10 screw.

    There should be a loop of cable coming from the motor as stated in step 18. Not visible on this picture. Can be misleading.

    Tonny - Reply

    Hi Tonny,

    Thanks for feedback. Loop is not visible, we will try to make a better picture.

    Martini H. - Official Prusa CS -

    Loop still not visible

    David Moore - Reply

    Maybe ship the upgrade with a ball end hex key if you expect this step to go smoothly. I m stuck here working with the tools I have.

    Christopher Rouxel - Reply

    Hi Christopher, we have included a ball-end allen key with all MK3 kits - you can use it now to finish the upgrade.

    Filip M - Official Prusa CS -

  35. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Fan-shroud (1x)

    • M3x20 screw (1x) (see info below)

    • M3nS nut (1x)

    • The fan-shroud was initially designed for M3x18 screw, but based on the feedback and to make the assembly more convenient, use M3x20. If your extruder bag includes only two M3x20 screws, please use another one from the spare bag.

    • The fan shroud is printed from ABS and located in the Upgrade bag.

    i needed an M20 elsewhere (for the fan assy) but the M18 (which I seem to have a lot of) worked fine here after screwing it up first with the M20.

    Julian - Reply

    Please mention that the fan shroud is located in the Upgrade bag. I was looking at all the parts I printed and could find it, then I though I dropped it and kept looking for it. Then I opened up the gcode files that I had printed parts from and the shroud was not even there. For about three seconds I was really mad thinking that Prusa screwed me over, then I came to my senses and realized that I should check the upgrade bag.

    Also, is there a reason why I Prusa decided to include this one part if we’re supposed to be printing our own parts? Why not just have us print it with everything else?

    Darrell Dudics - Reply

    Hi Darrell, we’ll mention that in description.

    We include it because it’s printed with ABS - and not everyone uses or wants to use it.

    Filip M - Official Prusa CS -

  36. Insert M3nS nut in the Fan-shroud, all the way in. Ensure correct alignment using the Allen key.
    • Insert M3nS nut in the Fan-shroud, all the way in.

    • Ensure correct alignment using the Allen key.

    • Mount the Fan-shroud to the extruder, secure it using an M3x20 screw. Don't over tighten the screw, you can break the plastic casing. Also make sure the fan can rotate freely.

    My fan shroud printed with an extra little piece for support, but I didn’t know it, so I put the shroud on with that piece still in place. It was the pictures that showed me it was extra.

    Rick Seiden - Reply

    Picture 2 is wrong, it cost me a few hours and one good fan shroud print that I kept cutting away on (luckily Prusa had sent me an extra one in the MK3S upgrade): The fan shroud is NOT LEVEL to the rest of the extruder as it appears to be in the picture, it actually protrudes from the rest about 1mm!

    Daniel K. - Reply

    On my upgrade (self-printed parts), the through hole in the extruder cover that matches the 4th extruder fan hole isn’t a through hole; it is apparently sized to be a ‘self-tapping’ fit for a 3mm screw, just as the other three extruder fan mounting holes are. This makes it impossible to attach the fan shroud without first drilling out this hole with a 3mm body drill. Am I missing something?

    Frank

    Frank Paynter - Reply

    Hi Frank, perhaps your printed overextruded a bit and the hole got thinner. You can drill it if it’s too hard to insert the screw.

    Filip M - Official Prusa CS -

    Didn’t notice at first, but the new fan shroud is included in the Extruder MK3S UPG bag even though it isn’t noted on the label.

    Thought I missed a self-printed part!

    gwizdavid@gmail.com - Reply

    This is for me the worst point in the mk3s construction by now. The hole in the extruder-cover for the M3x20 screw ist too small. It makes the screw not free sliding through but screwing through the plastic part. When the screw reaches the M3nS nut  it presses it first bevore screwing. But the worst point is, if you want to unscrew it again. It can happen (like in my case), that the M3nS nut  was pressed even more and broke the plastic parts.

    Luka - Reply

    I followed all the steps of positioning the hotend and looks like mine is rotated 90 degrees off. Please make it clear which rotation is correct with more images. I have to redo last 20 steps! So much wasted time…

    Martins Zeme - Reply

    Hello Mr Zeme,

    I just went through all of the photos here. There is only one correct orientation of the hotend and you can see it in all of the photos where you can see the hotend. It is also explicitly said and shown in the Step n. 14.

    Martin L. - Official Prusa CS -

  37. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Print fan (1x)

    • M3x20 screw (2x)

    • M3n nut (1x)

    • You need M3x20 screw due to its length. If you have used them accidentally somewhere else, head for the spare bag ;)

  38. First, slide the fan in the Fan-shroud and make sure it is aligned properly. Second, fix the fan in place using one M3x20 screw. Tighten carefully, or you will damage the fan's casing. Turn the extruder around and insert the M3n nut. No need to pull it in, we will use the screw.
    • First, slide the fan in the Fan-shroud and make sure it is aligned properly.

    • Second, fix the fan in place using one M3x20 screw. Tighten carefully, or you will damage the fan's casing.

    • Turn the extruder around and insert the M3n nut. No need to pull it in, we will use the screw.

    • Place the remaining M3x20 screw from the other side and tighten it, but carefully, or you will damage the fan's casing.

    • Guide the cable according to the picture in the channel. Bend it slightly towards the extruder. DON'T stretch the cable!

    3 M20 screws are necessary the kit has two as per earlier instructions without the extra parts would be short one screw.

    Frank Ferrucci - Reply

    The instruction that recommended the third M3x20 told you to grab it from the spares bag ;)

    Sijmen Schoon -

    Recommend adding a washer to the (2x) M3x20 screws that go through the fan casing. There is a warning to not tighten too much or you will damage the fan’s casing…but I still did it. A little super glue to fix the crack, and washers on the the screws fixed it right up.

    Jason Whatmore - Reply

    Exactly, and I also did the screw pull without the fan first, just to be sure not to break the fan casing

    Sijmen Schoon -

    Broke the second mounting hole in the fan when I first built the MK3, and had to superglue it. Broke it again while doing this upgrade, and have to glue it again. I *highly* recommend you change this step to require a small washer. Otherwise the way the screw head pushes on the thin plastic of the fan casing is just asking for trouble.

    Grant Root - Reply

    Hello Grant,

    Thank you for your recommendation, however, it is stated twice in this step in bold letters that it is necessary to tighten the screw carefully. We hope it might be enough of a prevention of trouble.

    Martin L. - Official Prusa CS -

    This was the hardest part for me up to this point. The fan didn’t line up with the shroud secured. I had to loosen the shroud, secure the fan, then secure the shroud.

    Brenda Bell - Reply

  39. For the following steps, please prepare:
    • For the following steps, please prepare:

    • P.I.N.D.A. sensor (1x)

    • Look of the sensor might slightly differ.

    • Check there are four wires in the connector, if not, call our support immediately.

  40. Insert P.I.N.D.A. sensor in the holder. Exact position doesn't matter, we will adjust it later.
    • Insert P.I.N.D.A. sensor in the holder. Exact position doesn't matter, we will adjust it later.

    • Tighten the M3x10 screw, but just slightly.

    • Create a loop on the cable from the sensor.

    • Push the cable in the channel together with the fan cable.

  41. For the following steps, please prepare:
    • For the following steps, please prepare:

    • FS-cover (1x)

    • M3x10 screw (1x)

  42. Place the FS-cover on the extruder and align it according to the picture. Tapered sides of the cover must be oriented towards you.
    • Place the FS-cover on the extruder and align it according to the picture. Tapered sides of the cover must be oriented towards you.

    • Insert the screw (mind the correct hole) and tighten it.

    • Tip: If you can't reach the nut, try to align it using an Allen key or pulling it up using a longer full-threaded screw from the spare bag.

    I just can’t screw this one.

    There is nothing to screw into.

    Omni Wired - Reply

    @OmniWired - I had this problem too. It was because the M3nS screw from Step 5 wasn’t pushed in far enough. The good thing is that I didn’t have to completely disassemble the entire thing to fix it.

    Jeremy - Reply

    Can you advise how you corrected this without completely disassembling?

    Travis Elijah -

    I also have the MMU2, which uses a QSM-M5 connector to the extruder. How can I use that with this upgrade?

    Jeremy - Reply

    m5 tap will work

    James Zimmerman - Reply

    Same same here, i will have to go back to step 5 :-)

    Eric - Reply

    I think this step should be moved back to around #21. I have accidentally touched the solder of the sensor a couple times…

    Russell McCampbell - Reply

    Same issue here. It really needs to be stressed more in step 5.

    Troels Larsen - Reply

    Hello Troels, Thanks for the suggestion, we will check it out.

    Martin L. - Official Prusa CS -

    After reading this I was careful in step 5 so I made sure that the M3nS screw was in a pushed in far enough. During the steps in between it must have slide out of position. Luckily I could just see the edge. With a needle and a lot of persuasion I was able to wrestle it back in position. Maybe in step 5 a dab of superglue to keep it from moving around?

    William E. Seyler - Reply

    Hello William, we always advise against the usage of superglue during the build as you might need/want to repair/upgrade the printer and then the nut would be stuck.

    Martin L. - Official Prusa CS -

    I couldn’t reach the nut so I tried an 18mm screw to pull the nut up. When the screw stopped turning in, I assumed it had grabbed the nut but when I went to back the screw out it would turn but not come out. The screw will turn in either direction but does not travel further in or come out. Tried to pull the screw straight out but it won’t budge. And in my efforts to hold the extruder firmly while I pulled and turned on the screw I managed to pull the power leads off the hot end. Time to order a new hot end and start disassembing the extruder to figure out what went wrong.

    sdollins@gmail.com - Reply

    So frustrating.. Just get us to put a temp screw in at step 5 to hold the nut. Happy to screw/unscrew it as necessary, getting to Step 42 and working out that something has shifted from back at Step 5 is about as frustrating as it gets..

    shaun@broadbent.cc - Reply

    Yep. What everyone else said. This is the most frustrating thing I’ve ever dealt with on a Prusa machine. My nut slipped just enough that I can’t grab it. I’ll end up just using a self-tapping screw I think because there’s no way I’m going to start the entire upgrade over again and risk messing up a delicate cable in the process.

    There has to be a better way.

    Andy Rickelman - Reply

    Same here. Fitting the m3ns nut in step 5 is crucial. It must not just be aligned, it must be pushed firlmy till it stops. Took me 10 minutes to umount what was needed to push it to its correct position (noctua fan + m3 10 from step 19 + step 22)

    Vincent Thinselin - Reply

    Well, on the bright side we got some extra practice assembling and disassembling the extruder =(

    Barry Hulce - Reply

    I have an MMU2 and the PTFE tube fitting doesn’t screw into this part. It does, however, screw into a very similar part that came as part of the upgrade and has a brass fitting inserted into it. Can I just replace the one part with the other? Where can I find instructions suitable for the MMU2s upgrade? I’ll note that the 10mm bolt I was using appears to be too short by a millimeter or two but I haven’t yet found a 12mm bolt to replace it with.

    Anne - Reply

    Hi Anne, it’s the normal MK3S extruder. The festo fitting with PTFE tube should be inserted into the MMU2S filament sensor cover (the chimney).

    Have a look here: 3B. MK3S/MK2.5S - extruder upgrade

    Filip M - Official Prusa CS -

    Same problem here. Can this cover be left off? Maybe just put a small piece of electrical tape to cover the sensor?

    Richard Boyhan - Reply

    Hello Richard, unfortunately not. The cover is essential, if you broke the part, try to reprint it. The models are available on our website.

    Martin L. - Official Prusa CS -

    May I make a suggestion that a screw be temporarily be inserted to keep the nut from moving?

    Richard Boyhan - Reply

    Hello Richard, sure, why not, just remember the screw is there just as a placeholder. :)

    Martin L. - Official Prusa CS -

    My suggestion is to update the instructions to add the screw being inserted, so that future users don’t experience the same frustration the rest of us have had with the nut slipping.

    Richard Boyhan - Reply

    THIS IS INCREDIBLY FRUSTRATING. I haven’t had a working printer in a year and a half, I can only work on it in short bursts every few days at most, and now I have to go back and repeat everything I’ve done in literally two weeks. This makes me want to carry the entire printer to the nearest bridge, drop the whole thing in the water, throw in all my clothing after it, and run screaming into the woods.

    WHY WOULD YOU DESIGN SOMETHING LIKE THIS? WHY!?

    Sam LG - Reply

    Hello Sam, what’s the problem?

    If you need assistance, you can always contact us via LiveChat: http://shop.prusa3d.com/

    Filip M - Official Prusa CS -

  43. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Zip tie (2x)

  44. Insert the zip ties in the X-carriage like in the picture. Lower the X-axis at about 1/3 from the top. Turn the printer like in the picture with X-axis motor and shorter extrusions facing towards you. Align the bearings similarly to the picture. The exact position of the lower bearing doesn't matter for now.
    • Insert the zip ties in the X-carriage like in the picture.

    • Lower the X-axis at about 1/3 from the top.

    • Turn the printer like in the picture with X-axis motor and shorter extrusions facing towards you. Align the bearings similarly to the picture. The exact position of the lower bearing doesn't matter for now.

    • Place the extruder on the bearings, the top couple must fit perfectly. Make sure the X-carriage is facing towards you (together with the shorter extrusions).

    • We will adjust the lower bearing later on.

    • Tighten and cut the zip ties.

    On step 40 you say to push the PINDA probe wire into the channel with the fan cable, then in this step from the picture you can tell that the wires were pulled out to the side in order to fit on the X-axis. However, you should state that the wires should be moved out to the side because even in the next step, you say to “push them back in the channel”. Why would we have to push them back if you never explicitly said to pull them away? So yeah, just to keep things clear.

    Darrell Dudics - Reply

    I printed the x carriage from the stl files on my Mk3 and the holes for the zip ties are not open enough and have spent many hours trying to get one in without luck. I am not sure if a claimer should be shown regarding if you opt to print the pieces yourself that there may be issues.

    chris gilreath - Reply

    Did you print it with 0.2 mm layer height and 20% GRID infill? That should ensure the parts will be printed correctly.

    Martin L. - Official Prusa CS -

    Thanks for the quick response Martin. Yes. Every other part fits well even the nuts fit. it is just the zip tie holes.

    chris gilreath - Reply

    i cut open the back to make an open channel at it works.

    chris gilreath - Reply

    Hello Chris, glad to hear it worked, but in general, we don't recommend cutting the printed part.

    For others reading this, it is better to reprint the part or purchase it in our online store.

    Martin L. - Official Prusa CS -

    I printed my parts in ABS and the zip ties didn’t fit either. Be careful if you decide to open the back channel as the sensor wire is right behind it.

    Jack - Reply

    Hi Jack,

    It can be tricky to print these parts in ABS as it tends to shrink. The recommended material is PETG.

    Martin L. - Official Prusa CS -

    Hi, I bought my MK3S upgrade with the printed parts, but when I put the X-carriage on the bearings they can move side to side. I’ve made sure they are seated properly, but it seems like either the bearings are too short or the carriage is a bit wide. Any help would be great.

    Cheers,

    Matthew

    Matthew Isenor - Reply

    Hi Matthew, it’s enough to tighten the bearings with zip-ties. Final tightening will be done with the backplate later.

    Filip M - Official Prusa CS -

    There really should be a section at the very beginning about how to check the parts before starting assembly. The top item there would be to test that zip ties fit through these slots. Mine fit, but I was amazed considering the many small trimmings and filings I’ve been doing throughout the build.

    Gary Boone - Reply

  45. Place the cables on the P.I.N.D.A. sensor side over the lower smooth rod and push them back in the channel. Place the cables on the hotend fan side over the lower smooth rod and push them back in the channel.
    • Place the cables on the P.I.N.D.A. sensor side over the lower smooth rod and push them back in the channel.

    • Place the cables on the hotend fan side over the lower smooth rod and push them back in the channel.

    • Align the bearing, so it fits nicely in the X-carriage

    For clarity, the two hotend wires (red and black - heater catridge/thermister) stay below the rod. (It’s hard to tell from the photo.)

    Mike McGlumphy - Reply

  46. For the following steps, please prepare:
    • For the following steps, please prepare:

    • X-axis belt

    • Use the belt from the disassembled printer.

  47. Insert the flat part of the X-axis belt  into the X-carriage as in the picture.
    • Insert the flat part of the X-axis belt into the X-carriage as in the picture.

    • Use a screwdriver or the smallest Allen key to push the belt in.

  48. Guide the X-axis belt through the X-end-idler, around the 623h bearing with the housing and back. Continue with the belt through the X-carriage. Guide the X-axis belt through the X-end-motor, around the GT2-16 pulley and back.
    • Guide the X-axis belt through the X-end-idler, around the 623h bearing with the housing and back.

    • Continue with the belt through the X-carriage.

    • Guide the X-axis belt through the X-end-motor, around the GT2-16 pulley and back.

  49. First, release the screw used later for fine tuning the belt tension. No need to remove the screw, just make sure it is loose. Please release two M3 screws on the X-end.
    • First, release the screw used later for fine tuning the belt tension. No need to remove the screw, just make sure it is loose.

    • Please release two M3 screws on the X-end.

    • Rotate the X-axis motor as indicated towards the frame.

    • Insert the flat part of the X-GT2 belt into the X-carriage as in the second picture.

    • Use a screwdriver or the smallest Allen key to push the belt in.

    • There might be belt overhang on this side, DON'T TRIM IT yet.

    for people upgrading, won’t we need to also release the angled tension screw at the top of the plastic piece?

    adcurtin - Reply

    Hi,

    Only if it’s actually being used.

    Filip M - Official Prusa CS -

    I have an early MK3 and there is no angled screw. Now what?

    srcarter@nebomanor.com - Reply

    Hi! In that case just skip the red bullet point.

    Martin L. - Official Prusa CS -

    I also have an early MK3 and there is no angled screw but there are also no slotted screw holes ( green circles) so I used the belt tensioning method as described in the original assembly instructions That is : loosening the left upper and right lower motor screws and “rotating” ( maybe 1mm ) the motor down. Then connect the belt and fasten both screws and then hope the belt tensioning is right.

    Peter Barends - Reply

  50. Using right hand rotate the motor to its original position and hold it (tension is applied to the belt). Using two fingers on your left hand push the belt together. Very small force should be needed for bending the belt, BUT the belt shouldn't be bent by its own weight before being pressed with your fingers, it must be straight.
    • Using right hand rotate the motor to its original position and hold it (tension is applied to the belt).

    • Using two fingers on your left hand push the belt together. Very small force should be needed for bending the belt, BUT the belt shouldn't be bent by its own weight before being pressed with your fingers, it must be straight.

    • If you are struggling to rotate the motor back into position, the belt tension is too high.

    • Depending on the belt being under or overstretched, adjust the amount of the belt in the X-carriage.

    • When done, rotate the motor to its original position and tighten the M3 screws again.

    This is the worst part in my opinion. Even if the tension here feels good you’re not going to know until the end and getting access back to the belt isn’t as easy as the Y-axis belt.

    My X/Y calibration failed, I added as much more tension as I could to this belt by pulling it farther in the teeth and tightening the motor and it passed calibration but the tension was at 286, which means I’m bound to have some layer shifting. I’m trying again but now my belt is slipping through the teeth when trying to rotate the motor to start tightening it…

    I feel like this is the next area that needs a design update. If the tension could be adjusted from the idler instead and adjusted even after the printer was fully assembled would be awesome.

    sir.different@gmail.com - Reply

    Hello, no worries, belt tension 286 can still be OK. Also, thanks for your feedback!

    Martin L. - Official Prusa CS -

  51. Both top and bottom part of the belt should be parallel (above each other).
    • Both top and bottom part of the belt should be parallel (above each other).

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

    • Tighten both screws on the pulley.

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

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

    • Move the extruder towards the X-axis motor. Don't use excessive force.

    • If the belt is stretched properly, you should feel a resistance and the extruder 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.

    • Belt too loose? Return to step 49 and repeat all steps until now. You have to rotate the motor and retighten the belt in the X-carriage. Shortening the belt length by moving one or two teeth outside X-carriage should be enough.

  53. Your belt might be already trimmed, simply skip the trimming instructions and insert it in the X-carriage. For the following step we recommend getting a white marker, but you can also trim the belt without it. Measure the part, which must be trimmed and gently take the end of the belt away, from the X-carriage, but make sure at least 3-4 teeth are still in the X-carriage, as you don't want to lose the tension. If possible make a mark, where to cut the belt.
    • Your belt might be already trimmed, simply skip the trimming instructions and insert it in the X-carriage.

    • For the following step we recommend getting a white marker, but you can also trim the belt without it.

    • Measure the part, which must be trimmed and gently take the end of the belt away, from the X-carriage, but make sure at least 3-4 teeth are still in the X-carriage, as you don't want to lose the tension. If possible make a mark, where to cut the belt.

    • Ensure again your mark is in the correct position and the belt is still stretched.

    • Using pliers cut the belt and push it inside X-carriage. Use screwdriver or Allen key, if needed.

    Use an exacto knife to cut the belt.

    Timothy Jacque - Reply

    Side-cutters / snips also work excellently for this. I have a set for bead and wire jewelry work that are on the smaller side and fit in the space nicely.

    M Castle - Reply

  54. In this step, we will finish tensioning the belt. Please read the instructions first, your belt might have proper tension already. First, slightly release all the screws holding the motor, otherwise, the upper "tensioner" won't work (the motor must be able to move). ATTENTION !!! BE EXTREMELY CAREFUL WHILE TIGHTENING, YOU CAN CRACK THE PART IF YOU OVER TIGHT THE SCREW.
    • In this step, we will finish tensioning the belt. Please read the instructions first, your belt might have proper tension already.

    • First, slightly release all the screws holding the motor, otherwise, the upper "tensioner" won't work (the motor must be able to move).

    • ATTENTION !!! BE EXTREMELY CAREFUL WHILE TIGHTENING, YOU CAN CRACK THE PART IF YOU OVER TIGHT THE SCREW.

    • Using Allen key start tightening the M3x18 screw inside the X-end-motor, but after each turn or two check the tension in the belt.

    • For the optimal performance, the belt must be a bit harder to press with your fingers. Move the extruder all the way to the X-end-idler and try the belt tension in the middle of the X-axis.

    • When you achieve optimal tension, please tighten the screws again.

    • In case you experience X-axis failure during calibration or skipped layers in the X direction, you can adjust this screw accordingly. Tightening the screw stretches the belt. Releasing the screw has opposite effect. Each time don't forget to release the screws on the motor first.

    There’s no tensioner on my system. Skipping this step. Is this ok?

    Jim Wade - Reply

    Yes, you can skip it and make sure you will adjust the tension correctly during the extruder assembly. You can also print yourself the latest version of this part with the tensionner.

    Martin L. - Official Prusa CS -

    How very very very disappointing it is to find out at step 54 that there is an updated part that brings a belt tensioner!!! The belt was the main pain part at assembling my early MK3 and without the tensioner, the assembly is even more frustrating now!!

    Please advise your customers in the beginning to print this tensioner update before disassambling the printer for the MK3S update!!!! *grrrr*!!!

    Extremly bad design without a tensioner and even without variable mounting holes of the x-axis motor.

    Guntor H - Reply

    Hello Guntor,

    Actually as an MK3(S) owner you should have the updated part already. My comment above is destined mainly to MK2.5(S) owners who might not have it. But yes it is quite handy. Either way, the printer is functional with both the old and the new part.

    Martin L. - Official Prusa CS -

    Well the date of issue of my invoice (I3 MK3 printer!) is 09/25/2017 and I got a printer without any tensioner on the x-axis motor mount. The motor is attached with 3 screws that go into perfectly round holes that are only about 1mm wider in diameter then the screws. There is no way to tighten the belt this way, it was a trail and error horror until I finally attached the belt at the x-carriage with the right amount of tension.

    With the MK3s design you make it even harder if you can do the tensioning only through the length of the belt.

    How come you say taht I should have the updated part? Did I miss an update that you sent out or did I get a beta version MK3??

    Guntor H - Reply

    Hi Gunthor, we announce new/updated parts every once in a while through our usual channels such as blog or newsletters.

    You can download STL files for those from here: https://www.prusa3d.com/prusa-i3-printab...

    There is no such thing as “beta” MK3, it’s just a normal process of updating plastic parts.

    Filip M - Official Prusa CS -

  55. For the following steps, please prepare:
    • For the following steps, please prepare:

    • Black nylon filament 50 cm / 19.7 inch (1x)

    • Your nylon filament should already have a tip on one end.

    The nylon guide was not in my upgrade package!

    Henk Heusinkveld - Reply

    Hello Henk. No worries, use the one you already have, or just continue without it. :)

    Martin L. - Official Prusa CS -

    Same here. No filament came with my upgrade kit.

    Martins Zeme - Reply

    Hi Martins, you should re-use the nylon piece that was part of your original printer assembly.

    Filip M - Official Prusa CS -

    Just to add I also didn’t have any nylon filament when I ordered my kit last year. Is it necessary?

    Martins Zeme - Reply

    Hi, the filament is used to hold the cable bundle. Without it there might be too much sagging.

    Filip M - Official Prusa CS -

  56. Locate the hole for the NYLON filament. Using the smallest Allen key ensure there are no obstacles inside. Using the pliers insert and twist the NYLON filament in the slot. Hold the extruder with your other hand. BE EXTREMELY CAREFUL as the pliers tend to slide and you can easily damage the wires!!!
    • Locate the hole for the NYLON filament. Using the smallest Allen key ensure there are no obstacles inside.

    • Using the pliers insert and twist the NYLON filament in the slot. Hold the extruder with your other hand.

    • BE EXTREMELY CAREFUL as the pliers tend to slide and you can easily damage the wires!!!

    • To check if the filament is seated properly, gently pull it with your hand. The X-axis should bend a little, but the filament must remain in the slot.

    • If you have issues, try to adjust the tip on the filament.

    Using the pliers insert and twist the NYLON filament in the slot. Hold the extruder with your second hand. -> Using the pliers insert and twist the NYLON filament in the slot. Hold the extruder with your other hand.

    Joe Reed - Reply

    Hello Joe, well spotted. Thank you!

    Martin L. - Official Prusa CS -

    insert the pointed end of the nylon filament into the hole.

    Ro.Yo.Mi - Reply

    I don’t know if you have fixed this since I did it with the MK3 about a year or so ago, but this part with the kit at that time absolutely sucked. I spent forever repointing and sanding and mashing the filament, using way too much force (large possibility of accidental damage), and when I got done I had to come up with a filament from the other side to bridge the strain relief as I’d lost too much filament.

    At the time there were several comments that this was the worst point in assembly… maybe it’s better with new kits, if not, there absolutely are multiple better ways to handle the strain relief joint than an interference fit (glue, a set screw, collar, an acute bend channel it locks into, whatever).

    Caleb B. - Reply

    A 1/8th inch drill bit, used very carefully, can widen the hole for the nylon filament just enough to ease insertion but still hold tension.

    Bryan Lakatos - Reply

    I will second the 1/8 drill bit to widen the hole. I did not have this issue with the original MK3 kit.

    parcival@gmail.com - Reply

    What is this even for? Would be great to know since I don’t have a nylon filament and maybe substitute it with something else if i know what this is for.

    Jordan Quah - Reply

    Hello Jordan, it just serves as a support, stiffening the cable bundle. You are not supposed to have a spool of nylon filament, we include a 50 cm piece in the box.

    Martin L. - Official Prusa CS -

  57. For the following steps, please prepare:
    • For the following steps, please prepare:

    • X-carriage-back (1x)

    • Cable-holder (1x)

    • M3x40 screw (1x)

    • M3n nut (1x)

    Don’t panic like I did—The cable holder comes from the old MK3 extruder. It’s not a new part.

    Amanda - Reply

  58. Prepare the M3x40 screw and cable-holder from the previous step. Tighten the screw all the way through the printed part.
    • Prepare the M3x40 screw and cable-holder from the previous step.

    • Tighten the screw all the way through the printed part.

    • Note there is a recess (slot) for the screw's head on one side of the printed part.

    I assume this is the cable holder from the old extruder? I don’t see where a new one was printed.

    Mike McGlumphy - Reply

    Hey Mike, it’s the MK3 or MK3S cable holder. You shouldn’t have to re-print it, as you already have it.

    Filip M - Official Prusa CS -

    The new one is included in the upgrade kit is identical to the MK3 version.

    Ro.Yo.Mi - Reply

  59. Take the M3n nut and place it in the printed part (all the way in). Use the screw pulling technique. Rotate the X-carriage-back and tighten it together with the cable-holder.
    • Take the M3n nut and place it in the printed part (all the way in).

    • Use the screw pulling technique.

    • Rotate the X-carriage-back and tighten it together with the cable-holder.

    • Check the "u-shaped" slot is aligned properly on both parts.

    How far down should the nut go? On mine it sticks up into the curved channel for the bearing. Should the nut be completely below the channel?

    Jay Sinnett - Reply

    Hi Jay, I confirm, that it should.

    Martin L. - Official Prusa CS -

    Yes, the nut should not stick up into the channel for the bearing. Of all the screw and nut cavities on the entire assembly, this is the only one that I needed to clean out with an exacto knife.

    Jay Sinnett - Reply

  60. Push the cables from the Extruder THROUGH the X-carriage-back. Start with IR-sensor cable, then the extruder motor and hotend fan. Next, add the print fan and P.I.N.D.A. sensor cables. Cables from hotend are NOT GOING through the X-carriage-back!
    • Push the cables from the Extruder THROUGH the X-carriage-back. Start with IR-sensor cable, then the extruder motor and hotend fan.

    • Next, add the print fan and P.I.N.D.A. sensor cables.

    • Cables from hotend are NOT GOING through the X-carriage-back!

    • Carefully insert the nylon filament and then slide the X-carriage-back towards the X-axis.

    “In the next step add the print fan and P.I.N.D.A. sensor cables” does NOT mean that they will be added in step 61. Add them now.

    Jay Sinnett - Reply

    Take the new cable from the filament sensor first, because it needs the most space to put through.

    Jan Bielawski - Reply

  61. For this step, please prepare: M3x10 screw (4x)
    • For this step, please prepare:

    • M3x10 screw (4x)

    • Before you tighten the X-carriage-back, arrange all cables, make sure none is pinched. Also make sure that the bearings are properly aligned.

    • Use all four screws and tighten the X-carriage-back.

    • Tighten the screws with a reasonable force, make sure you won't deform/squeeze the bearings between the printed parts.

    Top two screws don’t seem to sink tight, they move freely after tightening.

    joshua.armour@gmail.com - Reply

    Hey Joshua,

    It most likely means you have forgotten to insert the square nuts or the backplate is too far from the carriage.

    Filip M - Official Prusa CS -

    I have the same situation with the top two screws.

    scott.hockaday@gmail.com - Reply

    Hey Scott,

    It most likely means you have forgotten to insert the square nuts or the backplate is too far from the carriage.

    Filip M - Official Prusa CS -

    I had the same issue with the top right screw. It was not that I had forgotten the square nut, but that the square nut had a burr in the threads. I switched the nut (after testing) and it fixed the issue.

    Mr Gnome - Reply

    I had the same issue - no burr - nut was in - nut was located.

    Mine was deformation from the bridging under the screw head.

    Squeezed hard and the thread bit and squashed it

    Paul T - Reply

    Same issue with the top two screws. I switched to 12mm screws and solved the issue.

    John Radich - Reply

    Yes, use longer screws, then there is no issue.

    Jan

    JanV - Reply

    I had the same problem. The screws on top seem to be slightly short, I managed to get mine to work by squeeezing the joint closed with one hand then spinning the screw with the other, it engaged with about 2 turns.

    Ro.Yo.Mi - Reply

    This is the same problem that was mentioned dozens of times in the comments for the MK3 install. Screws are incorrect lengths for top. Also, if you tighten too much, the X axis will not calibrate. This should have been fixed in the docs and the build already.

    Neil F - Reply

    Hello Neal and everybody else. The thing is, we are testing the assembly many times before we decide about the length of the fasteners and the instructions in the manual, So maybe it’s a tight fit, but the M3x10 screws should really work. Please make sure that some fo the nuts didn’t fall off from the extruder carriage.

    Martin L. - Official Prusa CS -

    Nuts are defiitely there… the top two screws won’t catch and just spin freely.

    Daniel Wilday - Reply

    Hello Daniel, try using a longer screw to see if there’s something wrong with the nut. Perhaps it needs to be deeper inside the part.

    Filip M - Official Prusa CS -

    Hello Martin L and everybody else! I managed to get my screws to fit but the length is just wrong. You have to be very specific about the order you screw these in if you want a 10mm screw to fit. Not sure if the jump to 12mm is somehow uneconomical for you guys but it would save you some typing here at the very least.

    shaun@broadbent.cc - Reply

    I have used 12mm screw for the top two screws. I suggest to change it in the manual.

    Jan Bielawski - Reply

    Hi Jan,

    M3x10 screws should suffice, perhaps there was some extra printed material in holes in your parts? Also, if you start with top screw first, then it would be better to follow it up with tightening the bottom screw next on the diagonal while holding the part with your hand, so that it has flat contact with the extruder body. All screws should reach the threadings.

    Marcin M. - Official Prusa CS -

    Same problem, I released the two other screws to be able to put both parts closer on the top and it worked fine

    Paquay - Reply

    Leave other screws loose then two top screws go in easily. Then tighten all screws.

    ahill22600@gmail.com - Reply

    I also have problems tightening the top right screw which I fixed by using a slightly longer screw. Also when the screws are all tightened the x-axis had trouble moving, when I loosened these a little (so there was a slight gap between the back and the rest of the extruded) it moved freely again. Should I leave this gap or is there something I have done wrong here?

    Craig Nicholls - Reply

    Hello Craig,

    There should be no gap, both halves of the extruder body should be tightened flush against each other. Try to hold both parts tightly with your hand while screwing it in. It could be that the threading for the hole in the extruder body didn’t print correctly and it’s not catching on, in that case a longer screw is a good solution. However, seeing that there are many comments from users with a similar issue, we will look further into this with the production.

    Marcin M. - Official Prusa CS -

    Hi Marcin, as I outlined below the top bearings were just slightly out of place and once I moved them to the correct position it all fitted together and screwed into place easily.

    Craig Nicholls -

    Regarding there being no gap between the halves of the extruder body - if I tighten this so there is no gap then the carriage has great difficulty moving along the x-axis. If I then loosen the screws so there is a slight gap then it moves freely again. So I need to leave a gap otherwise I am pretty sure the printer won’t work.

    Craig Nicholls - Reply

    Hi Craig,

    No there definitely should not be any gap, please check the cables and the zip ties on the bearings.

    Martin L. - Official Prusa CS -

    Thanks Martin! I checked the bearings again and the top bearings were slightly to one side and I clicked them into place. After this the x-carriage back fitted flush and screwed in easily. I had checked this before and it wasn’t obvious that the bearings were out of place. If people are having trouble fitting the back x-carriage it may be worth seeing if this is a cause, at least it was for me.

    Craig Nicholls -

    Here I found out that I pushed the nylon wire in the M3 screw hole, it did fit.

    Marijn - Reply

    I needed to use a longer screw for the top right when upgrading my mk3.

    Chris Combs - Reply

    For me it was necessary to use M3×14 for the top screws. Impossible with M3x10.

    Christian - Reply

    ''''I also found one upper screw just spun. I just used a longer screw to pull it in, then switched to the M3x10. I suspect it was just the imperfections on the head side of the screw preventing it from going all of the way in, far enough to catch the nut.

    Gary Boone - Reply

  62. For the following steps, please prepare: Zip tie (5x)
    • For the following steps, please prepare:

    • Zip tie (5x)

    • Textile sleeve 13 x 490 mm (1x)

    • There are three textile sleeves in the package, use the largest one (both diameter and length).

    In the upgrade kit I received I only had one textile sleeve. It’s fine because I already have the other two, so maybe the doc just needs to be updated?

    Travis DePuy - Reply

    Hey Travis,

    The doc takes a few more scenarios into account.

    Filip M - Official Prusa CS -

    }Only one sleeve in my kit too. Shame I was hopping to replace the spiral sleeving on the X motor as well.

    Danny Sargent - Reply

    Only one sleeve here, too

    Frank Paynter - Reply

    I second that.

    Only one sleeve, which was a pitty because I too wanted to replace the plastic spiral for the x-motor.

    ludodg@gmail.com - Reply

    One sleeve here.

    Chris Combs - Reply

  63. Open one end of the textile sleeve and slide it on the cable bundle leading from the extruder. Don't forget to include the nylon! Leave the cables from the hotend out for now. Length of the first wrap should be slightly longer than the  cable-holder part, about 5 cm is enough.
    • Open one end of the textile sleeve and slide it on the cable bundle leading from the extruder. Don't forget to include the nylon!

    • Leave the cables from the hotend out for now.

    • Length of the first wrap should be slightly longer than the cable-holder part, about 5 cm is enough.

    • Gently twist the sleeve to make it smaller and tighter around the cables, orient the sleeve's seam downwards, then slide the sleeve towards the extruder.

    • Take 3 zip ties and insert them into the lower row of holes on the cable-holder.

    • Twist the sleeve again (without twisting the cables inside) and tighten the zip ties.

    • IMPORTANT: Cut the remaining part of each zip tie using pliers as closest to its head as possible. Note the correct position of each zip ties's head (slightly off-centre to the left).

    Twisting at first just rotates the sleeve, here’s how I did it.

    Hold the cables out straight, with some tension, so they won’t twist.

    With the same hand, hold the sleeve about 7-10cm back from the end.

    Twist the sleeve at the end.

    You basically need something to twist against and a way to stop the cables twisting.

    David Moore - Reply

    Before tightening the sleeves in the next step, be sure to test the fans with a 9V battery. I forgot to this (again), and the ground wire of my front print fan is now broken. I now have to cut the zip ties and disassemble everything, and my printer is out of commission for another week as I wait for a new a fan (that I had to buy myself).

    Timur Tabi - Reply

  64. Use two zip ties and push them through the upper slots on the cable-holder. ATTENTION! Before tightening the zip ties add the cables from the hotend. Use the channel in the printed part to arrange them properly. Once the hotend cables are included, tighten the zip ties and cut remaining parts.
    • Use two zip ties and push them through the upper slots on the cable-holder.

    • ATTENTION! Before tightening the zip ties add the cables from the hotend. Use the channel in the printed part to arrange them properly.

    • Once the hotend cables are included, tighten the zip ties and cut remaining parts.

    • Open the textile sleeve and insert the cables from the hotend.

    • Compare the look of the cable management with the last picture.

    • The zip tie arrangement was tested with the injection molded double spool holder (provided in the kit and assembled later on). If you intend to use any other frame mounted type holder, make sure the zip ties won't crash into it, which might result in a print failure.

    There are some forum comments that the hotend wires are getting damaged by the screw in the heated bed cable cover facing up. Make sure the wires from the hotend sit up into the channel at the bottom of the two parts of the backplate.

    George - Reply

    this should really be added to the instructions. there are hardly any photos even showing the channel and its easy to miss once you are at this step. There is no mention of its existence. Also I notice the channel has a hole on one side (the left when looking at the front of the printer) as if perhaps a zip tie or something else was meant to go there to hold things in place. I feel like this part was just not thought through very well.

    joseph chagan -

    This will not work with the heatbed cover replacement used with the IKEA Lack enclosure. I damaged my hotend wires when they scraped against it during XYZ Calibration. :(

    Scott - Reply

    Is it ok if the red hotend sheath wire is touching where it connects to hotend? i was not sure if it would melt,

    chris gilreath - Reply

    Hi Chris, it depends. The cable should not directly touch the heater block.

    Martin L. - Official Prusa CS -

    The design of the cable holder is flawed and needs to be fixed. Attaching the hotend cables to the bottom frequently results in a damaged cable. I discovered that my cable was already damaged before performing this upgrade.

    Prusa, you need to create a new design that carries the hotend cable UP and not just out. The slot for the hotend cable bundle is too small, and there is nothing that holds the bundle in the slot. I was able to improve my wiring by removing the zip tie around the cable bundle. The two thicker cables are attached to the holder as normal, and the two thinner ones are off to the side.

    Timur Tabi - Reply

    Dear Mr Tabi,

    please make sure to arrange the cables exactly as shown on the photos. If you do so, the cable cannot get damaged.

    Martin L. - Official Prusa CS -

    I stand by my comment. I think it’s a design flaw to have the cables attached so low, and the slot really is too small to hold all the wires. It could be made wider. Lots of people have connected everything correctly and the cable still gets damaged.

    Timur Tabi -

    Mr Tabi,

    The thermistor and heater cables always have to be led from below. Some people are (somewhat understandably) afraid to use all 3 zip ties as instructed and to tighten them properly so that the cables won’t be hanging down. It’s a tight fit, agreed, but certainly not a design flaw since it’s not an issue for the majority of printers.

    Martin L. - Official Prusa CS -

    The criteria for a “design flaw” should not be that it works 51% of the time.

    Also, these cables undergo millions of fatigue cycles in under a year with normal, weekly use (that’s my estimate, but wouldn’t you agree?). In under a year my heater cartridge leads had fatigued/corroded through and failed. The glass wrap/insulation on the thermistor cartridge had fatigued through and the leads were likely to soon fail when I replaced both cartridge and thermistor.

    Any input about improving stress relief, routing, and also chemically protecting these leads (thermal decomposition products of PLA, etc., are likely corrosive, no?) should be appreciatively received, in my opinion. You’ve done an exemplary job on the whole with the engineering, but it can still be much, much better.

    Caleb B. - Reply

    A picture showing the hotend cables would be greatly appreciated!

    Dave Nelson - Reply

    Hi Dave, those cables are visible on all 3 pictures. Do you have something else in mind?

    Filip M - Official Prusa CS -

    Got to this step and saw one of the hotend cables broke. Everything was going so smoothly up until this step.

    John T. - Reply

    when tightening all zipties you have no slack in the thermistor- and heatercables which is needed when working on the hotend, changing a nozzle

    ludodg@gmail.com - Reply

    Concerned at this point while testing the lateral end stop. The extruder structure doesn’t reach the end stop. The cable wrap presses against the upper frame and RAMBo box. Going to try undoing the wire holder and sleeve and see if I can thin them down at all.

    Jayme Cousins - Reply

    Hi Jayme, if you have MK2.5S, then you also need to install the extruder endstop block.

    If it’s MK3, then make sure your textile sleeve is properly squeezed and zip ties are tightened according to the manual.

    Filip M - Official Prusa CS -

    Since there is a bunch of discussion on this step and the official answers don’t really give an answer that was satisfactory: the solution to the wires getting too close to the screw on the heated bed is covered in Step 2 of the Electronics Assembly (basically, add an extra nut to the protruding screw, on the other side of the bed, so the screw becomes shorter and doesn’t protrude out)

    Also: do try to get the wires into the little notch in the extruder (not shown in the pictures), as it lifts the wires a bit away from the previously mentioned screw.

    Rcmaniac25 - Reply

    The description mentions a channel in the printed parts to guide the hot end wires though, however there is no clear photo of this channel or the wires fitted through it.

    Be aware of this channel and guide the wires through it, otherwise you will most likely damage the hot end wires by catching the screw on the bed heater wiring cover.

    A clear photo from the rear/under side of the extruder assembly would have been a good idea. It seems too little too late judging by some of the previous comments :(

    Luke Carmichael - Reply

    Hi Luke, a photo will be added, plus we have changed the design of the HB cable cover. All the screws are now facing down.

    Jakub Dolezal -

  65. Are we there yet? Almost!
    • Are we there yet? Almost!

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

    • Checked everything? Let's move to: 4. Electronics assembly

    Orange is my favorite color so I printed all parts in Prusa Orange.

    Granted, this might be a problem for the sensor which I will find out … but it GREATLY improved the ease of assembling.

    Working on the orange parts was much easier to see then on black parts, with black wires, black zipties, a black sleeve …

    ludodg@gmail.com - Reply

Finish Line

259 other people completed this guide.

Jakub Dolezal

Member since: 02/20/2017

217 Guides authored

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29 Comments

I also have the MMU2, which uses a QSM-M5 connector to the extruder. How can I use that with this upgrade?

Jeremy - Reply

took me 2.5 hours

dito milian -

Hi Jeremy,

If you are already an MMU2 owner, you will receive the MMU2S Upgrade Kit for free - in there, you will find fs-cover-mmu2s plastic part which is used to connect the PTFE with QSM-5 to the extruder.

3B. MK3S/MK2.5S - extruder upgrade

Marcin M. - Official Prusa CS -

I think that took about 2 hr.

The instructions were easy to follow. Huge thanks for all the pictures too!

-B

Byron Wingerd - Reply

Hello,

You can send us the feedback about assembly time directly by clicking Suggest a time next to Time required :)

Marcin M. - Official Prusa CS -

Is anyone else experiencing that firmware 3.6 for Mk3S is not working right with the new filament sensor? I loaded Hatchbox Silver and it loads fine bu then as it goes through its 9 points it errors out and says filament not loaded?

almonster@yahoo.com - Reply

Hi,

It might be related to mistakes with the E axis assembly.

Have a look here, perhaps it will help you: https://help.prusa3d.com/article/43mduc4...

Filip M - Official Prusa CS -

In step 6 (Filament lever) I see something happening that is not as described:

When I put in the long magnet, such that it repels the short one, when I slide it fully in, the short magnet jumps out of its slot. That’s no problem: I can slide it in later. But in step 14, where I should punt the motor on top, I cannot hold the short magnet and prevent it to jump out and glue itself to the gear. Playing around and trying to get it right, the long magnet got away and broke in half. I’m glad I have a spare! Any suggestions how to handle this?

Len - Reply

(Comment split in more pieces because the length will not be accpeted)

Phew! I got it all in. Here are some manipulations that proved helpful in the end:

* I held the hot end in place using a tie wrap around the hot end cooling ribs and the extruder body. That freed up a hand while trying to get the motor in place. The tie wrap can be removed after the extruder-cover has been placed.

* I could never have taken the picture in step 6 with the green tick mark, as the magnets won’t stay in place as shown there: one jumps out of its slot as the other is fully inserted. Did I get magnets with differently oriented fields?

Len -

* I used a very flat piece of plastic: PETG, 0.8 mm thick, around 10 mm wide and 30 mm long. I had it lying around in the form of a band cable clip. It may be helpfull to print a piece like that up front, before disassembling the printer. I used it to prevent the short magnet from jumping out of its slot from the moment the long magnet came into place up to the time that the motor was like 2 mm above its final position. It worked!! The motor is in place, and so are the magnets.

* As a final test that the magnets are properly oriented, you can slide in the test filament from step 10, see the fs-lever move away and, on filament removal, see it move back again.

Len -

* The teflon tube in the hot end must be made to protrude from the silvery base for no more then 13.0 mm or it will prevent the gear from turning, and it will prevent the motor from being mounted properly: the tube prevents the gear from coming down sufficiently towards the tube. I had to try a few times before the teflon tube descended sufficiently into the hotend: perhaps because my hot end was actually used instead of being virgin? It can be measured with calipers (slide gage: very useful tool for every 3d printing afficionado) and it can be tested by trying to turn the gear with your finger nails after mounting the motor: you should be able to turn it. Try to turn it before mounting to get a feel for the resistance you should expect from the motor alone.

Len -