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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

  2. This is the most important and hardest chapter, take your time, don't rush. Properly assembled extruder is essential.
    • 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.

    • The hotend for MK3S/MK2.5S MMU2S needs a shorter PTFE tube compared to the MK3/MK2.5 MMU2 (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, printed parts. Don't worry if you finish with few unused items.

    • The package also include magnets, which are used on the single material version and are not needed when assembling the MMU2S upgrade. We include them as an extra if you decide to switch to single material.

  3. For the following steps, please prepare: Extruder-body (1x) M3x10 screw (1x)
    • For the following steps, please prepare:

    • Extruder-body (1x)

    • M3x10 screw (1x)

    • M3nS nut (2x)

    • M3n nut (2x)

    • Adapter-printer-mmu2s

    • The package should include only the orange adapter. If you have printed parts yourself, please don't use the version with the hole for the steel ball.

    • Specific MMU2S printed parts are included in the MMU2S Extruder Bag.

  4. Take two M3nS nuts and insert them in the Extruder-body. Make sure both are all the way in.
    • 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.

  5. 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: use the Bondtech gears recovered from your printer. Also, 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 ;)

    • Reuse the Extruder motor from the disassembled printer. Don't use the Extruder motor from the MMU2S kit, the cable is not long enough.

  6. 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.

  7. 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.

  8. 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.

  9. For the following steps, please prepare: Hotend for MK3S/MK2.5S (1x)
    • For the following steps, please prepare:

    • Hotend for MK3S/MK2.5S (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.

  10. Take the orange Adapter-printer-mmu2s (without hole for steel ball) and insert it in the Extruder-body.  The surfaces of both parts should be almost aligned. DON'T use any screw to secure the Adapter-printer-mmu2s. It should hold inside the Extruder-body by itself.
    • Take the orange Adapter-printer-mmu2s (without hole for steel ball) and insert it in the Extruder-body. The surfaces of both parts should be almost aligned.

    • DON'T use any screw to secure the Adapter-printer-mmu2s. It should hold inside the Extruder-body by itself.

    • 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 might be missing.

  11. Hotend assembly was completely reworked from MK3/MK2.5 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.
    • Hotend assembly was completely reworked from MK3/MK2.5 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.

  12. 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 the extruder motor assembly on the Extruder-body.
    • 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 the extruder motor assembly on the Extruder-body.

    • 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.

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

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

    • M3x18 screw (1x)

    • M3x10 screw (1x)

    • M3n nut (1x)

    • FS-cover-mmu2s (1x)

    • IR-sensor-holder-mmu2s (1x)

    • IR-sensor-cover-mmu2s (1x)

    • The list continues in the next step...

  14. For the following steps, please prepare: Prusa IR-sensor (1x) M2x8 screw (1x)
    • For the following steps, please prepare:

    • Prusa IR-sensor (1x)

    • M2x8 screw (1x)

    • MK3S and MK2.5S share the same IR-sensor, but need different communication/power cable:

    • IR-sensor cable for MK3S (1x)

    • IR-sensor cable for MK2.5S (1x)

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

  15. Take the smaller connector WITHOUT THE SENSOR! and carefully push it all the way through the IR-sensor-holder-mmu2s. Once the connector is through, connect the cable and the sensor together.
    • Take the smaller connector WITHOUT THE SENSOR! and carefully push it all the way through the IR-sensor-holder-mmu2s.

    • Once the connector is through, connect the cable and the sensor together.

    • Make sure the safety latch is facing up.

    • The sensor must be facing down.

    • Pictures show MK3S IR-sensor cable, but use the same procedure for the MK2.5S cable. This is valid for the entire manual.

  16. Take the IR-sensor and place it in the holder, make sure the orientation is the same as in the picture. Take cover and place it on the top. The cover is asymmetrical, see the picture.  The smaller gap in the cover should be on the left. Secure the IR-sensor and the cover using an M2x8 screw.
    • Take the IR-sensor and place it in the holder, make sure the orientation is the same as in the picture.

    • Take cover and place it on the top. The cover is asymmetrical, see the picture. The smaller gap in the cover should be on the left.

    • Secure the IR-sensor and the cover using an M2x8 screw.

  17. Carefully insert the cable in the channel, make sure it is all the way in. Take the FS-cover-mmu2s and push in the M3n nut. Slide the holder on the cover, again make sure it is all the way in, otherwise, the holes won't align properly.
    • Carefully insert the cable in the channel, make sure it is all the way in.

    • Take the FS-cover-mmu2s and push in the M3n nut.

    • Slide the holder on the cover, again make sure it is all the way in, otherwise, the holes won't align properly.

    • Secure both parts using an M3x10 screw, see the picture for the correct hole.

    • This entire IR-sensor assembly is also called "chimney" in the Handbook.

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

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

    • X-carriage (1x)

    • M3n nut (2x)

    • M3nS nut (4x)

  19. 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.

    • In case the nuts keep falling out, use short screws from the spare bag to fix them temporarily.

  20. Place cable in the X-carriage, use the small printed overhangs to keep the cable inside. Gently place the FS-cover assembly on the rear side. The length of the cable isn't important for now, we will adjust it later. Guide the cable through the slot, remember this path, we will use it for other cables as well.
    • Place cable in the X-carriage, use the small printed overhangs to keep the cable inside.

    • Gently place the FS-cover assembly on the rear side. The length of the cable isn't important for now, we will adjust it later.

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

  21. 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.

  22. 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 from the back of the extruder.
    • 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 from the back of the extruder.

    • 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.

    • Good job! Grab one extra gummy bear ;)

  23. Flip the FS-cover assembly on top of the Extruder. Align the left edge with the extruder body. Use a M3x18 screw to join both parts together.
    • Flip the FS-cover assembly on top of the Extruder.

    • Align the left edge with the extruder body.

    • Use a M3x18 screw to join both parts together.

    • The IR-sensor cable can go straight in the extruder, no need for any additional loop. Carefully pull the cable, contrary if the cable is stretched, push it slightly in.

    • Finish the sensor assembly by inserting an M3x40 screw.

    • Make sure all the gaps are gone.

  24. 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.

    • In case of the upgrade from MK3/MK2.5 the fan was fixed using M3x18 screws, switch them for M3x14.

  25. Now you can tighten screws on both sides. 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.
    • Now you can tighten screws on both sides.

    • 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.

  26. 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!

  27. 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.

  28. For the following steps, please prepare: Extruder-idler-mmu2s (1x) Bondtech WITHOUT the hole for the lock screw (1x)
    • For the following steps, please prepare:

    • Extruder-idler-mmu2s (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

  29. 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.

  30. Take M3n nut and place it in the Extruder-idler-mmu2s. 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-mmu2s.

    • 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. In case of a self-printed part, please drill both holes for the shaft with a 3mm drill before inserting the shaft.

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

  31. 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.

    • It is recommended to create a tip on the filament. It will be easier to insert it all the way into the PTFE tube.

    • 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.

  32. Place the Extruder-idler-mmu2s 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 (though the range of the movement is small).
    • Place the Extruder-idler-mmu2s 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 (though the range of the movement is small).

  33. Use the M3x40 screw with the spring to introduce tension to the Extruder-idler-mmu2s. Hold the Extruder-idler-mmu2s on the other side, until the screw reaches the nut.
    • Use the M3x40 screw with the spring to introduce tension to the Extruder-idler-mmu2s.

    • Hold the Extruder-idler-mmu2s 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.

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

    • Print-fan-support (1x)

    • M3x10 screw (1x)

    • M3n nut (1x)

  35. 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.

  36. 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.

  37. 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 fan's plastic casing. Also make sure the fan can rotate freely.

  38. 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 ;)

  39. 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!

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

    • P.I.N.D.A. sensor (1x)

    • IMPORTANT there are two sensors, which are similar. Learn the difference:

    • P.I.N.D.A. sensor - 4 wires, used previously in the extruder, use it now

    • F.I.N.D.A. sensor - 3 wires, part of the MMU2S package, will be used later on

    • Look of the P.I.N.D.A. sensor might slightly differ, namely the colours.

  41. 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.

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

    • Zip tie (2x)

  43. 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 with X-axis motor and PSU facing towards you. LCD is on the other side. 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 with X-axis motor and PSU facing towards you. LCD is on the other side. 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 with the "belt inserts" is facing towards you.

    • We will adjust the lower bearing later on.

    • Tighten and cut the zip ties.

    • Check all the square M3nS nuts are still in the X-carriage.

  44. 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

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

    • X-axis belt

    • Use the belt from the disassembled printer.

  46. 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.

  47. 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.

    • Note that MK2.5 has a slightly different X-end design, namely the absence of the tensioning screw from the top.

  48. MK3 owners only: 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.
    • MK3 owners only: 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.

  49. 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.

  50. 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.

  51. 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 48 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.

  52. 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.

  53. If you have MK2.5, please skip this step. 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).
    • If you have MK2.5, please skip this step.

    • 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.

  54. 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.

  55. 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.

  56. 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)

    • MK2.5S extruder differs from now on! Please use another chapter and then return here. MK2.5S extruder cable management Follow the linked chapter to the very end, apart from the cables you need add one printed part (Endstop-block).

    • MK2.5S users only: after you return back to this chapter, you can skip to the Step 64.

  57. 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.

  58. 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.

  59. 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.

  60. 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.

    • 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.

  61. 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)

    • The MMU2S includes a textile sleeve for the oldest MK3/MK2.5 designs, use it to replace the spiral wrap.

  62. 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).

  63. 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.

  64. Carefully and quietly open the bag with the Haribo sweets.  High level of  noise might attract nearby predators!
    • Carefully and quietly open the bag with the Haribo sweets. High level of noise might attract nearby predators!

    • Sort the bears into six rows according to the following scheme (colours might differ):

    • Previous and current chapter were very difficult, at least 25 % of total amount is needed.

    • Idler assembly is quite easy, 10 % is enough.

    • Pulley body assembly requires your attention, eat no less than 20 % of all bears.

    • Electronics assembly is the last chapter with high level of difficulty, consume 25 %.

    • Spool holders with the buffer are easy to make, research shows that 10 % is enough.

    • Preflight check is almost effortless. Experienced user will require no more than 10 %.

  65. Are we there yet? We are just getting started! Important info only for those, who are upgrading from MMU2 to MMU2S (MMU2S unit already assembled), you can skip to chapter 6. Electronics and MMU2S unit assembly (Step 23)
    • Are we there yet? We are just getting started!

    • Important info only for those, who are upgrading from MMU2 to MMU2S (MMU2S unit already assembled), you can skip to chapter 6. Electronics and MMU2S unit assembly (Step 23)

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

    • Don't worry about the cables, we will connect them later ;)

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

Finish Line

311 other people completed this guide.

Jakub Dolezal

Member since: 02/20/2017

225 Guides authored

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Prusa Research Member of Prusa Research

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367 Guides authored

15 Comments

Took about 1 hour 45 min to do this, plus another 15 for connecting the electronics after. Not too bad.

Kenji Castro - Reply

It seems there is a step missing from this guide, the Endstop Block is not installed in this guide as part of the MK2.5 -> MK2.5S upgrade.

Steps 64-65 could be copied from the following guide to cover this:

3. E-axis assembly

Brent W - Reply

As mentioned above in the comments, it’s in Step 56 as a bullet point. But I agree it could be a separate step, I’ll report it and see what can be done.

Martin L. - Official Prusa CS -

Hi Brent,

there is a reason behind the current guide layout (overall guide maintenance). Please follow the linked guide and then return here.

Jakub Dolezal -

ahh, I see, so I just missed the link. I am okay with that, I had thought that the Endstop Block wasn’t mentioned at all in these guides.

Thanks for looking into it!

Brent W -

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