This is a stackable horizontal spool holder inspired by RagingRoosevelt's design (but modeled from scratch). I made it to hold 5 spools of 1kg standard size filament but you could add or remove levels as needed for your setup. My main goal was to minimize the desk space needed for the spools for my MMU.

If you want to build this, you will need the following parts for each level in addition to the 3D printed ones:

• 4x 608 bearings (these are the size that came with the spool holders in the MMU2S kit and you shouldn't need any additional ones if you have that kit). 608ZZ and 608RS will both work fine.
• 4x M3x8mm socket head screws (to hold the bearings in place, but you could modify the model slightly and rely on a press-fit instead)
• 1x PC4-M10 fitting to connect PTFE tubes to the filament feed support

For a 5-level system like I made for the MMU2S, you'll need 5 times the above supplies. The notes on each model file include the quantities you will need for each part, assuming 5 levels.

All of the printable parts fit on the MK3S+ bed without issue. You will need supports when printing the following parts (I changed overhang threshold to < 45° since it handles the chamfers without issue and painted the filament hole to avoid supports generating there):

• Tall supports: to support the hex bump out on the top
• Filament feed supports: to support the hex bump and the filament passthrough
• Platter: print face down and add supports for the little 1mm recess for the spool aligner

I was able to assemble without glue and it holds securely, but Gloop or CA glue can be used if things are coming apart or loose at all.

If you want to feed the filament out the other side of the tower, you should be able to simply mirror the filament feed supports in your slicer and assemble accordingly.

Each level has a platter to support the spool and a separate swappable part that inserts into the platter to keep the spool aligned. I've included two sizes of the aligner in the model files that fit the spools I have. You can also adjust the parameters in these two OnShape models to support other sizes:

• This OnShape model is used if the spool center hole is smaller than 55mm
• This OnShape model is used if the spool center hold is larger than 55mm

The full OnShape model is available here. Please let me know if you make changes, I'd like to see what you improved!

Note that in the photographs, my version has a slightly different top cross-member and tall support design. I reworked it after printing so that the tall supports are the same for each level. Assembly is the same for both versions, just slide the top cross-member on the 3 tall top supports.