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9B. MK3S+ / MK3.5 Extruder mod (KIT)

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9B. MK3S+ / MK3.5 Extruder mod (KIT)

9B. MK3S+ / MK3.5 Extruder mod (KIT)
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Last updated 2 months ago
9B. MK3S+ / MK3.5 Extruder mod (KIT)
 Difficulty
Very difficult
 Steps
39
 Available languages
CSPLDEESITFR
Tools necessary for this chapter
Tools necessary for this chapter
Tools necessary for this chapter
Please prepare tools for this chapter:
Needle-nose pliers
1.5mm Allen key for nut alignment
2.5mm Allen key for M3 screws
A measurement tool (optional), a digital caliper would work the best.
Printer preparation
Printer preparation
Printer preparation

This chapter will describe a modification of the single-material MK3S+ / MK3.5 extruder to accomodate MMU3.

Keep all the parts. Some of them will need to be re-installed back in place.
Before you start, make sure that:
The filament is unloaded and the print head is at a height it is easily accessible at.
The printer is properly cooled down and the steel sheet has been removed.
The printer is turned off and unplugged.
On the MK3.5 printer, ensure you have easy access to the electronics box on the left side.
MK3S+ Releasing the cable bundle
MK3S+ Releasing the cable bundle
MK3S+ Releasing the cable bundle
In order to use MMU3 on your MK3S+, a few components on the print head need to be changed. First, we need to release the extruder cable bundle.
If you use MK3.5 printer, skip two steps ahead.
Using an Allen key release the M3x40 screw on the electronics box and open the door on the other side.
Release two M3x10 screws and remove the extruder-cable-clip on top.
In case there are zip ties holding the cables inside the electronics box, carefully cut and remove them.
MK3S+ Unplugging the IR filament sensor cable
MK3S+ Unplugging the IR filament sensor cable
MK3S+ Unplugging the IR filament sensor cable
Carefully unplug the IR filament sensor cable and make sure it is free inside the electronics box.
We need to gently pull the IR filament sensor cable slightly towards the extruder as the sensor will be in a different position. Make sure the entire path of the cable is free. However there is no need for a complete disassembly.
MK3.5 Releasing the cable bundle
MK3.5 Releasing the cable bundle
MK3.5 Releasing the cable bundle
MK3.5 Releasing the cable bundle
This step is valid for MK3.5 printer only. If you are using the MK3S+, skip to the next one.
Remove four M3x6 screws holding the xBuddy cover. Remove the cover.
Remove the two M3x18 screws holding the front part of the cable holder and remove the Ext-cable-holder-a part.
Carefully cut and remove the zip ties securing the cable bundle, taking care not to damage any cables.
We need to gently pull the IR filament sensor cable slightly towards the extruder as the sensor will be in a different position. Make sure the entire path of the cable is free. However there is no need for a complete disassembly.
X-carriage-back disassembly
X-carriage-back disassembly
X-carriage-back disassembly
X-carriage-back disassembly
Cut and remove all the zip ties on the cable holder behind the extruder.
Release the textile sleeve on the cable bundle by pulling it back slightly. Usually, there is no need to remove it completely.
Remove all four M3x10 screws on the X-carriage-back part.
Split the x-carriage about 10 mm (0.4 inch) apart in the back to ensure the cables will be able move through more easily.
FS-cover and hotend fan disassembly
FS-cover and hotend fan disassembly
FS-cover and hotend fan disassembly
FS-cover and hotend fan disassembly
Release and remove the M3x10 screw on top.
Remove the FS-cover. It will be replaced with a new one.
Release the M3x40 Idler tension screw with the spring on the side. You can leave it in place.
Release the M2x8 screw, unplug and remove the IR filament sensor.
Be careful with the IR filament sensor, hold it by its sides. Try not touching the components on the PCB. Keep it in an ESD-safe place.
Release both M3x40 screws on the front, just few turns to create about 0.5cm (0.2inch) gap in the extruder body.
Release and remove all screws holding the Hotend fan on the side. Remove the fan. We need to reach a screw behind the fan.
Extruder-body disassembly
Extruder-body disassembly
Extruder-body disassembly
Extruder-body disassembly
Release and remove the M3x40 screw on the back holding the Extruder-idler on the side.
Remove the Extruder-idler from the printer.
Remove the other M3x40 screw on the back.
From now on, try keeping the extruder parts together as it can easily fall apart while it’s not being held together by the screws!
Using an Allen key, push the black Adapter-printer part up. Keep in mind there is a steel ball inside, which usually falls out. Remove the part entirely.
We will replace Adapter-printer part with a new part.
IR Filament sensor cable
IR Filament sensor cable
IR Filament sensor cable
IR Filament sensor cable
Find the IR filament sensor cable inside the cable bundle and move it from the electronics box towards the extruder slightly.
Grab the wires of the IR filament sensor cable and try gently pulling it up to the top of the extruder.
Don't pull hard on the cable.

Push the cable towards the extruder from the electronics box, while you are pulling the cable on top. This way, the cable should slide without a significant resistance.

Combine gentle pushing and pulling on the cable to avoid damage.
We aim to get 6cm (2.4in) of the cable above the top of the extruder body.
Hotend PTFE tube INFO
Hotend PTFE tube INFO
Hotend PTFE tube INFO
Hotend PTFE tube INFO
VERY IMPORTANT INFO! READ CAREFULLY!!
There is a short PTFE tube inside the extruder’s hotend. It plays a major role in the MMU operation. This tube cools down a molten filament tip to form a narrow sharp end on it, while the MMU does a material change.
The tube is considered a consumable as it wears down over time during the regular use. Therefore, it should be replaced once in a while, after the printer went over certain amount of material changes. We strongly recommend replacing it now, since the extruder is partly disassembled already.

A new hotend PTFE tube has a 1.85mm internal diameter. If your printer is new or very lightly used, you can skip the PTFE replacement in the upcoming steps and proceed to "Adapter-printer parts preparation."

The specimen on the right, however, was taken off a printer after approx. 20000 material changes, using a high-temperature abrasive filament that wore down the tube’s bore up to 2.4mm. This caused increased stringing and malformed filament tips, leading to frequent MMU filament loading problems on that machine. The worn PTFE tube needed replacement.

Splitting the extruder
Splitting the extruder
Splitting the extruder
Release both M3x40 screws at the front, just below the extruder motor. Don't remove them completely. We will use them to hold the extruder parts together.
Carefully split the extruder apart by pulling the front out.
Create approx. a 1cm (0.5in) gap similar to the one seen in the picture.
Partial extruder disassembly
Partial extruder disassembly
Partial extruder disassembly
Reach for the hotend and incline its upper part towards the motor. Wiggle it to slide it down.
If the hotend is still stuck inside, release the screws below the motor some more to increase the gap between the printed parts.
BE EXTRA CAUTIOUS with the hotend cables!!! You can break them! Use a reasonable force to pull the hotend out. Don't bend the cables too much.
PTFE tube parts preparation
PTFE tube parts preparation
PTFE tube parts preparation
For the following steps, please prepare:
Hotend PTFE tube (1x)
PTFE for MK3S+ is 42.3mm long, 1.85mm ID, 4mm OD, inner chamfer on one side, outer chamfer on the other.
The bundled PTFE tube is intended for MK3S+ only. The PTFE tubes  for MK3S and MK3S+ differ in length.
Old PTFE tube removal
Old PTFE tube removal
Old PTFE tube removal
Press the black plastic collet.
Remove the PTFE tube from the hotend.
While the black collet is still pressed down, push the PTFE tube in and then pull it out. This way, you will disengage the small metal hooks inside the black collet first. If you force the PTFE tube out without the hooks properly disengaged, the PTFE tube can jam inside.
Throw the worn-out PTFE tube immediately to the nearest trash bin to avoid installing it back by accident ;)
New PTFE tube installation
New PTFE tube installation
New PTFE tube installation
New PTFE tube installation
Now it is time to insert the new PTFE tube. Note, that each end of the tube is different.
One end of the tube has an outer chamfer. This end must be inside the hotend.
The other side has an inner chamfer. This conical shape is the filament entry. This part must be outside the hotend.
Push the PTFE tube in. Slide it all the way in and hold it!

Using your other hand pull the collet out while you keep pushing the PTFE tube in. THIS IS CRUCIAL for the hotend to work properly.

After you finish inserting the new PTFE tube, check that the whole hotend is tightened up and nothing got loose during the process.
Extruder reassembly (Part 1)
Extruder reassembly (Part 1)
Extruder reassembly (Part 1)
Extruder reassembly (Part 1)
Re-insert the hotend back into the extruder. Ensure its orientation is the same as seen in the picture.
IT IS CRUCIAL to ensure the hotend is fitted properly in the extruder-body!!! The top of the hotend must fit into the correct recesses in the printed parts. See the second and the third picture for a reference!
Extruder reassembly (Part 2)
Extruder reassembly (Part 2)
Extruder reassembly (Part 2)
Check once again the correct position of the hotend. Look from below the extruder. The heater block should be oriented as seen in the picture. Perpendicular to the printed parts, with the cables pointing to the back.
Guide the thermistor cables above the thick heater cables.

Take a look from the side of the extruder. The nozzle should be slightly below the printed fan-shroud. 

If it is significantly lower than in the picture, your hotend isn’t inserted correctly.

Extruder reassembly (Part 3)
Extruder reassembly (Part 3)
Extruder reassembly (Part 3)
Carefully and slowly push all the parts together.
In case of any significant resistance STOP immediately and check, which part is blocking the movement.
Tighten the two M3x40 screws on the front of the extruder slightly - just so that the extruder parts are held closer together. We will tighten the screws fully later on.
Adapter-printer parts preparation
Adapter-printer parts preparation
For the following steps, please prepare:
Adapter-printer-mmu (1x)
The package should include only the orange adapter. If you have printed parts yourself, please don't use the version with the hole for steel ball. (used for single-material printers)
Adapter-printer assembly
Adapter-printer assembly
Adapter-printer assembly
Insert the Adapter-printer into the opening on top of the extruder-body. See the protrusion, it must fit into the groove.
Push it down until it’s flush with the surface.
New chimney: parts preparation
New chimney: parts preparation
For the following steps, please prepare:
Chimney base (1x) with the Tappex Microbarb 0006-M5 threaded insert
Chimney (1x)
M3nS nut (1x)
M3 washer (1x)
M3x30 screw (1x)
M3x18 screw (1x)
New chimney assembly (Part 1)
New chimney assembly (Part 1)
Take the Chimney part and orient it as seen in the picture.
Insert the M3nS nut into the marked opening on the bottom of the printed part.
New chimney assembly (Part 2)
New chimney assembly (Part 2)
New chimney assembly (Part 2)
New chimney assembly (Part 2)
Add Chimney base onto the extruder. Note the correct orientation on the picture.
Make sure the cable is above the Chimney base and oriented as seen in the picture.
Slide the Chimney onto the base part from the right side.
Make sure the cable goes through the channel on the bottom of the Chimney base and goes out on the right side.
Fix the parts together by M3x18 screw. Tighten it up just so that the parts hold on the extruder. Don't tighten it up fully yet. We will need to move the parts later on.
New chimney assembly (part 3)
New chimney assembly (part 3)
New chimney assembly (part 3)
New chimney assembly (part 3)
Insert the M3x30 screw into the marked opening on the side of the Chimney Base. Screw it in until it pulls the chimney all the way in.
Stop tightening after you feel a slight resistance. Do not over-tighten the screw!
Insert the M3 washer into the marked opening on top of the Chimney Base.

Push it all the way in so that it locks the screw head in place.
Make sure the screw head is behind the washer. This way, you will be able to move the chimney precisely in both directions, by rotating the screw.
Using the 2.5mm Allen key, adjust the position of the washer so that it is centered and you can reach the screw head underneath later on.
IR Filament sensor: parts preparation
IR Filament sensor: parts preparation
For the following steps, please prepare:
Chimney cover (1x)
M2x8 screw (1x) you removed from the printer earlier
Prusa IR filament sensor (1x) you removed from the printer earlier
IR Filament sensor assembly
IR Filament sensor assembly
IR Filament sensor assembly
IR Filament sensor assembly
Attach the IR filament sensor onto the top of the chimney.
Make sure the electronic components on the sensor board are facing down and the three connection pins are in the back.
Add the cover onto the sensor.
Using the 1.5mm Allen key, lock the cover in place with the small M2x8 screw.
Look at the back of the extruder. Connect the cable to the filament sensor.
Make sure the safety latch on the connector is pointing up and the connector aligns with the pins.
If you plug the connector incorrectly, you can damage the eletronics!!!
Extruder-idler disassembly
Extruder-idler disassembly
Now, take the Extruder-idler part you removed from the extruder earlier. We need to get the Bondtech gear, the bearings and the shaft out of it.
The printed part will be replaced with a new one.
Using a 2.5mm Allen key, push the shaft out. Keep it for later use.
Take the Bondtech gear out, BUT BE CAREFUL, there are two bearings inside. Don't lose them!!!
Extruder-idler-mmu parts preparation
Extruder-idler-mmu parts preparation
Extruder-idler-mmu parts preparation
Extruder-idler-mmu parts preparation
For the following steps, please prepare:
Extruder-idler-mmu (1x)
Make sure you’re using the correct new part.
Bondtech gear (1x) you have removed from the original idler before.
Needle Bearing (2x) you have removed from the original idler before. Might still be inside the gear.
M3n nut (1x)
Shaft (1x) you have removed from the original idler before.
PrusaLube (1x) the supplied lubricant
Bearing assembly & Greasing
Bearing assembly & Greasing
Bearing assembly & Greasing
Bearing assembly & Greasing
Add a tiny bit of lubricant into the needles in both of the bearings. Wipe off the excess grease to prevent spreading it all over the place.
Insert both bearings into the Bondtech gear. Make sure the bearings do not slip out during the assembly.
Add a tiny bit of lubricant into the geared part of the Bondtech gear.

Make sure the lubricant doesn’t get into the filament groove.

Do not use excessive amount of lubricant. Just a tiny bit will do.
Extruder-idler-mmu assembly (Part 1)
Extruder-idler-mmu assembly (Part 1)
Extruder-idler-mmu assembly (Part 1)
Extruder-idler-mmu assembly (Part 1)
Take M3n nut and place it in the Extruder-idler-mmu2s.
Use the screw pulling technique.
Insert the Bondtech gear into the idler as shown in the picture. Make sure the geared part of the Bondtech is on the side of the plastic part with the cutout.
Slide the shaft in through the idler and the Bondtech gear. Use reasonable force to prevent breaking the plastic part.
Extruder fasteners parts preparation
Extruder fasteners parts preparation
For the following steps, please prepare:

M3x40 screw with spring (1x) (Extruder Idler tension screw. Might be still in the extruder.)

M3x40 screw (2x)
M3x20 screw (1x) (Extruder fan bottom corner)
M3x14 screw (3x) (Extruder fan)
There were two versions of the Extruder fan supplied. Most printers have Noctua fan, but if you have Delta fan, there are slightly different M3x16b and M3x22b screws. Use the screws you removed from the fan earlier.
M3x10 screw (4x) (x-carriage-back)
Extruder reassembly
Extruder reassembly
Extruder reassembly
Extruder reassembly
Fully tighten the two M3x40 bolts at the front of the extruder.
Add the fan to the extruder and push it to the back. There are cables behind the fan. You can GENTLY push the cables into the dedicated channel using an Allen key.
Before you proceed to attach the fan, make sure all the cables are inside the channel.
The fan has two sides, one has a sticker with markings on it. Make sure, this side is facing to the inside of the extruder.
Fix the fan using the following screws (depending on the fan version):
M3x14 / M3x16b screw (3x)
M3x20 / M3x22b screw (1x) in the bottom corner.
Extruder-idler-mmu installation
Extruder-idler-mmu installation
Extruder-idler-mmu installation
Extruder-idler-mmu installation
Add the Extruder-idler-mmu onto the extruder.
Add two M3x40 screws into the openings at the back of the extruder. Tighten them up slightly.
Do not overtighten the screw holding the extruder-idler part. Otherwise, the idler won't be able to move freely.
Add the M3x40 Idler tension screw with the spring into the opening on the left side of the extruder.
Hold the idler with one hand while you tighten the tension screw from the other side. The screw head should be aligned or slightly below the surface. That way, the idler is pulled with the correct amount of force.
X-carriage-back reassembly
X-carriage-back reassembly
Now, look from the back of the extruder. Gently push the X-carriage-back part in towards the extruder. Ensure no wires are pinched between both parts and that the cables engage into the dedicated channels properly!
Tighten all four M3x10 screws.

Tighten the screws with a reasonable force.

In case the top two screws are tightened up excessively, the top two bearings will resemble a V-shape, the axis won’t be able to move correctly and the top X-axis rod will get damaged. Tighten the top screws just lightly. Remember, the top two bearings are secured by the zip-ties - so the top two screws do not have to be overly tight.

Zip-Ties!
Zip-Ties!
For the following steps, please prepare:
Zip tie (7x)
Tightening the textile sleeve
Tightening the textile sleeve
Tightening the textile sleeve
Gently twist the sleeve to tighten it up around the cables. Slide the sleeve towards the extruder.
Take 3 zip-ties and insert them into the lower row of holes on the cable-holder.
Tighten up the sleeve around the cable bundle (without twisting the cables inside). Hold it tight while you fix it in place with 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 (pointing up)
Attaching the hotend cables
Attaching the hotend cables
Attaching the hotend cables
Push two zip-ties through the upper slots on the cable-holder. Tighten the zip-ties up slightly around the hotend cables.
Arrange the cables from the hotend into the dedicated channel on the bottom.
Tighten up the zip-ties and cut the remaining parts of the zip-ties.
Attaching the cable bundle
Attaching the cable bundle
Attaching the cable bundle
Let’s move onto the electronics box side of the cable bundle.
Tighten up the sleeve around the cable bundle. Hold it tight before you fix it in place with the clip and the screws. The textile sleeve should be held by the cable clip
Fix the cable bundle in place by tightening the two M3x10 screws holding the Extruder-cable-clip. Make sure no cable is getting pinched!
For easier cable-management inside the electronics box, attach the extruder cable bundle to the hooks on the inside of the Einsy-base with two zip-ties in the marked positions.
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