Prusa MMU3 or ERCF universal buffer, takes 900mm filament, mounts on IKEA Skadis or stand, USS compatible

Welcome, you MMU3 or ERCF users.

I was kind of fed up with the spools standing around my Core One with MMU3 (former MK4S) so I installed 2 IKEA Skadis boards behind the printer to mount the spools. However, the Prusa buffer used a lot of space and it is not very flexible, since I like to feed from my drying boxes. I tried gravity holders and auto rewinders, but these did not convince me. I have been looking around for solutions until I stumbled over DiscoJon's concept, which I really liked. However, his concept integrates a spool holder and is made for standing, not solving my space issue. Thus I made a very rough remix in the slicer by removing the spool holder, adding a peg for the new Prusa USS boxes and 2 holes to take the universal Skadis peg. It worked, but took a long time to print and used quite some filament. As well, it can only take the Prusa MMU3 spindle only to the right side.

So I sat down and re-designed the concept from scratch in FreeCAD.

Advantages to the original concept:

• single piece print, uses less material, takes 900mm filament

• you can use it in ANY direction on a peg board (Skadis) - the spindle can point in the direction you need

• you can use any spoolholder compatible with the Core One mounting holes (links of my preferred versions below), even USS boxes (not tested, but should work)

• you can mount them on a stand and add up as many as needed (but you need long screws) to feed from dryers directly

• you can make your own stand to your liking

Printing intructions:

The buffer on its own prints in one piece, using only 135g of PLA and can take up to 900mm (!) of filament - I measured it. It needs to be printed upright, standing on the slot for the original Prusa buffer spindle. I added some seam painting on the in- and outside (see photos) to reduce nasty sink marks. I used the 0.25mm "structural" profile with 0.4HF nozzle and mostly standard settings. Just changed to gyroid infill + 5mm brim. This model prints in 5h15m as single piece! Do not try to print a single (!) instance with "speed" or "balanced" settings  - the overhangs will collapse, due to insufficient cooling. If you print more than one piece, you get away with "speed" or "balance", since the layer times will be longer. It should print on smaller printers as well (turned 45°), but you need minimum 210mm of z height.

Assembly instructions:

• To hang it on a Skadis board, you need to print 2, better 3 Skadis pegs which mount in any of the outside holes with M3x10 screws

• I have added a stand for it (Jan 27th 2026), which in my case takes 2 buffers and stands next to my dryer. You should be able to fit more than 2 buffers to feed a 4 spool dryer, but you need very long screws. The stand just clicks together. The clearance is 0.2mm - works perfectly on my Core One

• As a spoolholder, you can use the Prusa USS spool holder for the Core One+ or the really nice PTFE spoolholder, which can be found here (needs at least 2 additional M3x16 screws):

https://www.printables.com/model/1486513-prusa-core-one-to-core-one-upgrade-community-versi

https://www.printables.com/model/1288055-prusa-core-one-ptfe-spoolholder

• You also need an assembled MMU3 spindle (found under "buffer for all printers R4", wheel & segment + screws, nuts and a bearing), which can be found here:

https://www.printables.com/model/531604-mmu3-printable-parts

• Add a small piece of PTFE to the inlet and now you can mount it in ANY direction - with the spindle to the right, as per the photos, or to the left (flip around, it is symmetrical), top or down - however you like it and where you need it. It hides nicely behind the spool. 

• The holes are equipped with sockets for M3 nuts, since I plan to add a stand, so you can place it anywhere. It also enables me to combine 2 or more of these buffers to mount to my dual or single spool dryers. So more to come, but you are welcome to design these on your own and post a remix - looking forward to your ideas!

Please respect the license. No commercial use, but feel free to remix :-)

Version history:

December 4th 2025 - first release

December 12th 2025 - update model V2.1 - added the original Core One cut-outs in the model, so it can take all Core One spoolholders in any direction. Revised tolerances

January 27th 2026 - added a stand to feed from dryers