Self-contained Original Prusa Enclosure + MMU Mod

The main difference between this and other mods is that it uses the stock buffer unit and encloses it within the enclosure itself, making the entire setup self-contained. I originally built the enclosure for the MK3S+/MMU2S in late 2023/early 2024. I've since upgraded the printer and MMU to MK3.5/MMU3, and it fits just as well. The mod should equally work for MK4/MK4S with the MMU3. 

Main features

• All 5 spools for the MMU, as well as the buffer unit, are contained within the enclosure.

• Includes PTFE tubing to easily bypass the MMU, for when the printer is to be used with the MMU disabled.

• Compatible with the following addons:

  • Hinged lid (required, would be a pain to change filament without it)

  • Fire suppression system

  • LED strip (moved to the top)

  • PSU quick release

  • Advanced filtration system

Assembly guide

This guide may be incomplete because I don't have all the information to hand at the moment. This build was done over several months, on and off. I went over many iterations of trials and errors during that time. I didn't keep a good record of that build process, so don't necessarily remember which models I ended up using and which ones I ended up discarding. I will go back to determine the sources for the final build and update this guide accordingly.

This guide is brief because I don't have time to write a comprehensive guide for now. I'll come back and add details later when I have time.

Materials

Assuming you already have the MMU3 including the buffer unit, print:

• 3 upper spool holders, including 1 mirrored (for front top left)

• 2 lower spool holders (elogated), including 1 mirrored

• 3 spool holder arms (reuse the 2 existing ones from the printer for a total of 5)

• 2 middle filament guides (one is the mirror of the other)

• 1 filament guide with integrated hygrothermometer

• 1 filament guide for top front right

• 2 dual filament connectors

• 1 quad filament connector

• 3 LED spacers

You'll also need the following (*I got these from RS Components):

• PTFE tubing, ID 2.5mm, OD 4mm* (#232-8386)

• Festo fittings, QSM-M5-4* (#121-6037)

• M3 x 8 and M3 x 18 screws and M3n nuts

• Molex 5-way male CLIK-Mate to 5-way male CLIK-Mate wire to board cable for LED strip, at least 650mm* (#15135-0506)

Procedure

Insert festo fittings into the quad filament connector and dual filament connectors. Install the quad filament connector on the top right, close to the front, with an M3 x 18 screw and M3n nut. Install the dual filament connectors on the top left and top right, close to the rear.

The PTFE tubes connect the front filament guides at the front to the festo fittings in the quad filament connector on the top right of the enclosure. Insert the PTFE tubing into the front filament guides and route them behind the top front and top right of the enclosure for spools 1-4, and insert the other end into the quad filament connector, like this: https://i.imgur.com/E0LoIh8.jpeg. Feed the filaments through the filament guides at the front, through the PTFE tubing and quad connector, into the buffer unit.

For spool 5 (rear top left), connect the PTFE tubing between the two dual filament connectors via the festo fittings. Route this around the top rear of the enclosure. Insert a 15-25cm PTFE tube on the other side of the dual filament connector and leave it dangling. Load the filament clockwise, and feed the filament front to rear by inserting it into the dangling end of the PTFE tubing, like this: https://i.imgur.com/KaXcjX5.jpeg. 

For the buffer, no need to attach the leg. Place the buffer where the printer PSU used to be, with the segments/cassettes facing up: https://i.imgur.com/nvIaeBk.jpeg. Connect the segments/cassettes with the PTFE tubing to the quad/dual filament connectors on one end, and to the MMU on the other. Avoid abrupt bends in the PTFE tubing - a larger radius is better for lower friction. I'll update the guide with PTFE tube length later.

For single-filament non-MMU mode (for using the printer with the MMU disabled), use the remaining slot in the dual filament connector closest to spool 5 (top rear left). Attach a PTFE tube from the front-facing festo fitting in the dual filament connector to the extruder. Insert a segment of 10-15cm PTFE tube into the rear-facing festo fitting and leave that end dangling. Load the filament anticlockwise, and feed the filament into the dangling PTFE tube, from the rear to the front of the enclosure. When printing with the MMU disabled, use spool 5.

More details later. See photos for now (photos with captions here). Some photos are of the older MK3S+/MMU2S setup, but it's pretty much the same for compatible MK3/4 series + MMU3 setups.

To move the LED strip to the top, I had to extend the cable. The longest cable I could find was 600mm, but even that was still a few cm too short. I ended up buying two of that, cutting them and soldering them together. I then replaced the short stock cable with the longer cable.

Origins and sources

This mod was originally shared on Reddit. It uses various models from other authors, in combination with some models that I've created myself. The models uploaded here are my own. Links are provided to models sourced from other authors.

My own sources

STL and FCStd files are provided. The FCStd files are editable in FreeCAD.

• LED spacer: Use this to increase the distance between the LED strip and the enclosure, to accommodate some PTFE tubing. 

• Quad filament connector: Use this to route filaments 1-4 from the front to the right of the enclosure.

• Dual filament connector: Use this to route filament 5 from the top rear left to the right of the enclosure, and to route the filament directly to the extruder when bypassing the MMU.

• Front top left filament was pending but have now been added as filament-guide-3a/b.stl.

Other sources

These are used as-is: 

• Original Prusa Enclosure printable parts: https://www.printables.com/model/251931 

  • The stock spool holder is used for the upper spools. Simply mirror the model during slicing, if necessary.

• MMU3 printable parts: https://www.printables.com/model/531604

  • Use the stock buffer unit from this source. 

• Spool holder arm with solid tags: https://www.printables.com/model/516999

  • I tried other spool holder arms without the solid tag, but the tags broke. This model has strengthened tags.

• Filament guide with integrated hygrothermometer: https://www.printables.com/model/501895

• Middle filament guide for front lower spools: https://www.printables.com/model/506025

• Spool holder for lower spools: https://www.printables.com/model/512278 

  • These are elongated compared to the Prusa stock, to raise the spool a bit higher. Otherwise, it's difficult to change the spool due to the printer frame being in the way. The same model is used for both the left and right spools, by simply mirroring the model during slicing.

The following parts are optional.  If you have the original MMU3 parts, you don't need these. I used them initially when I first adopted the MMU3 buffer unit to use with my MMU2S. I had printed all plastic parts to assemble the buffer but I still needed the metal pins and the metal collettes. I didn't have the MMU3 upgrade kit at the time so I looked for printed alternatives and found these, which worked great: 

• Buffer segment/cassette with printed shaft: https://www.printables.com/model/852926

• Collettes for buffer segment/cassette assembly: https://www.printables.com/model/599675

Print settings

I printed these parts in generic PETG, typically at 0.20mm layer height, 15-20% gyroid infill, without supports. The spool holder arm was printed at 100% infill.