Prusa MK3S+MMU2S Filament Feeder System

I recently got my long awaited kit for Prusa MK3S + MMU2S, exited by the thought of being able to create parts in different colors - and even types. I had not read too much up front, but after the order was placed I began doing some research. Seeing warnings about MMU2S being a beast to handle did not scare me....thinking that I am quite tech savvy, Oh man was I wrong! The building of both the 3d printer and the MMU2S was a great and fun experience - but it was the easy part.

I tried for hours and days just to get a the MMU2S change the filament getting more and more crazy. Problems with filament feeding, IR sensor issues, pinda calibration. My god I was regretting the whole thing and was getting very close to crush the whole thing with the biggest hammer in my workshop!

Something had to be done. My biggest problem was the filament feeding system issued with the printer. It was big & clunky and - to my experience - gave WAY to much friction fr the filament to come all the way to the MMU2 unit. After fixing the IR sensor issues this was the problem to be attacked.

Guess there is many solutions to the problem out there but what's the fun of that - I had to make my own :D

My approach:

Feed the filament from "bottom-up" hence ensuring no bended PTFE in the back of the machine. Any bends here will give issues for the bond gears in the MMU2 unit.

There must be a buffer for the filament retracted from the unit. I saw someone using old spools for this but this just takes too much space. So I made my own compact version of this

Reuse. In good Prusa spirit tweak, adjust and make reuse of surplus hardware. The (useless in my opinion) spool holders gave a great starting point. Both the bearings in the kit and the 8mm rods are used in this setup. If you do not have these parts from before you must source them yourself.

See the pictures - it should be self explanatory.

I used PLA for the filament base - since I at that timne had not gotten PETG for my machine. If you use PLA - there could be NO WARPING. Even the sligthest warp will destroy the model since the margins are small. I recommend to use PETG. Never printed with this material before now and I am a fanboy...will never by PLA again :D

For the buffer spools the spool sides must be glued so that filament does not get yammed.

In the filanent spooler there is one 608zz bearing in each spool. Use m3x15 for putting on the plates. For the spool buffers there are two 608zz bearings - one pushed in from each side.For me - this solution has solved every problem with feeding the MMU2S with fresh material. There is absolutely NO FRICTION when the filament is loaded, hence the bond gears in the MMU2S has no problems getting the filament to the extruder. When the extruder takes over pulling filament there is of course a bit more drag but no problems for the machine. The bearings in both the spooler and the buffer makes everything go smooth.

I hope this can help someone else than me from crushing their machine. I am actually starting to like this addon and the fantastic opportunities it gives!!!!

The original Onshape file is here if you want to fork and tweak:

The STLs are available on Thingiverse here:


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