MMU Filament Carousel

This is a space-saving, tabletop alternative to the vertical spool mounts Prusa provides with their printers and MMU upgrades.  The concept consists of 5 independent spool holders that stack into a single tower.  Each spool holder is fitted with a ring-shaped ball bearing followed by a hollow base, allowing the spool to rotate freely and independently from the rest.  A segmented tower provides holes for the PTFE tubes that feed the MMU, as well as “bridge” pieces to stabilize the stacked assembly.  The modular design allows 1 to 5 spools to be stacked and easily swapped.

**NOTE: Each spool holder requires a ring-shaped ball bearing to allow the spool to rotate; a bearing with a 35mm bore diameter fits perfectly.  These are the bearings I used: https://a.co/d/6NAKZJe

Description of components:

• Base:  Single unit that integrates the first spool holder and base for the PTFE tower.  I put spare anti-slip pads on the bottom which help keep the assembly in place during printing.
• Spool holder:  Provides the stationary, stackable base for each rotating spool. 35mm center shaft fits the ball bearing described above.  The mounting section at the top is inserted into the bottom of the next spool holder, and these are notched to prevent unintended rotation.
• Spool ring:  Slides over the spool holder and sits on top of the 35mm ball bearing.  The spool will then mount over the ring, allowing it to rotate freely.  Sized to work with Prusament and most other filament spools.
• Tower section:  Stackable segment aligning with each spool holder assembly.  The tower provides the holes for the MMU's PTFE tubes, as well as a slot for the “bridge” supports that stabilize the entire assembly.
• Bridge:  A removable part that fits on the top of each spool holder assembly, and mounts to a slot in the corresponding tower segment.  Provides stability for the fully stacked and loaded carousel assembly.
• Tower clip:  A removable clip that can be installed between each tower segment to secure the connection and further stabilize the PTFE tower.  
• Tower spacer:  During assembly, it may be necessary to raise the tower segments 1-2mm to maintain alignment with the stacked spool holders.  These 1mm thick spacers will do the trick!
• Spool holder cap:  Decorative cap for the topmost spool holder in the stack.

Printing:

I printed all components with PLA, 0.20mm layers and 25% infill.  Supports are recommended for spool holder and spool ring.

Assembly:

1. Add non-slip pads to the bottom of the base (optional, the spares from your printer or MMU kit are perfect!)
2. Add a 35mm ball bearing to the spool holder in the base.
3. Add a spool ring which will rest on the bearing, then add a filament spool.
4. Add a tower segment to the base; secure with a clip and insert PTFE tube that feeds the first MMU buffer.
5. Add a bridge to the top of the spool holder, insert the other end into the slot in the tower segment.
6. Add additional spool holders and tower segments as needed, following steps 1-5. 
7. Add spool holder cap to the topmost spool holder.

Tip: I would advise that you assemble the entire stack without filament spools first.  Make sure the tower is straight and the bridge pieces are level between the spool holders and tower segments.  It may be necessary to add one or more tower spacers, and/or slightly shorten the bridge pieces to achieve a fully aligned stack.

Usage:

The base assembly + 1 tower segment can be used by itself as a single-spool mount.  Add or remove a spool holder assembly and tower segment to support up to the 5 filaments that can be loaded to the MMU.  As long as your printer and this assembly are on a solid, stable work surface you should not experience any issues with the fully stacked carousel assembly while printing.