(Non-Auto-Rewind) Spool Holder for RepRack

On my quest for a good way to feed my LACK-housed Mk4S/MMU3 from RepRack-mounted filament spools above, I looked at a number of alternatives to Prusa's spool buffer, which doesn't really work great with my setup. Among other things, I investigated a few auto-rewinders, none of which worked reliably enough for me to trust them in a production environment. What I settled on instead is shown in https://www.printables.com/model/1130321 – I'm not using any buffer.

(Update 5-8-2025: I have finally found a rewinder that appears to be much less finicky than everything else I tried: the Filamentalist).

I had a handful of Jerrari's auto-rewinder spool holders lying around from from my experiments so why not use them to feed the filament from the RepRack, after removing all the coils and clutches (which, alas, in my hands always ended up binding at one point). I find this roller style more versatile and easier to use than Repkord's own RackRollers or RackStand. However, the way the cylinders are inserted into the frame didn't really work for me; I kept knocking the rollers out of the frame with my fat fingers when swapping filament. 

So I made this remix, which uses small protrusions on each side to snap into the 608 bearings and hold the rollers securely in place. None of the other frame parts were changed. While I was at it, I changed the threads in the cylinder bodies and caps to open and close the usual way (righty tighty). For the sake of completeness, in the 3mf files provided, I also include frnktrgr's excellent remix of the original front frame part, which adds a PC4-M10 pneumatic connector for PTFE tubes.

Version 1.1 – 05-08-2025: Added a front frame part with 2 (two) PC4-M10 connectors.

BOM

8x M3x6 screws (M3x8 screws also work fine)

8x M3 nuts

4x 608 ball bearings

1x PC4-M10 connector

Unlike Jarrari's original, no need for spray-coating the rollers.

Assembly

What I found easiest is to first put the nuts into their respective openings and secure them with what Prusa's assembly manuals call the “screw pulling technique”. Then fasten the base to the two sides with the M3x6 screws. The sides are symmetrical, so orientation doesn't matter. Now firmly push the ball bearings into their openings in the cylinder caps and cylinder bodies and screw the cap on the body. Slightly bend the two sides apart and slide the openings in the ball bearings onto the protrusions. Unlike in the original, orientation of the cylinders doesn't matter. Finally secure everything by attaching the front and back parts with M3x6 screws.  

STEP file included.

If you like what I'm doing…

 … consider buying me a coffee or joining my Club.