Creality Space Pi spool holder

If you're doing any kind of reverse Bowden thing, you know that any resistance when pulling filament into the extruder is a bad thing, and the Space Pi's dinky little 624Z bearings with their 4mm ID and shafts have an awful lot of resistance.

This series of parts offers a way to improve that:

• Common 608 (skateboard) bearings integrated into a large diameter spool holder for low rolling resistance
• Self-centering, lift-out/drop-in mating geometry for easy installation and removal of the filament spool
• Optional reuse of the stock 4mm rods for additional rigidity (some spools might need them removed)
• Crowned spool holder to keep the spool from walking off the holder
• Chamfers to make the lid close easily, even if things aren't centered

You can also customize the spool holder to meet your specific needs, or if you want a more robust version you can also make the spindle out of metal with a lathe.

Construction

To build the full assembly, you'll need

• 2x wedge (suggest flat side down)
• 2x stand (suggest non-chamfered side down)
• 2x pulley of diameter of your choice (thick side down)
• 1x spindle (vertical; support suggested) OR both halves of the split spindle (vertical, brim suggested)
• 2x M3x10 (or longer) screw
• 2x M3nN nut
• 2x 608 (rollerskate) ball bearings; open for minimal resistance, shielded (e.g. Z) or sealed (e.g. 2RS) variants will also work

If using the split spindle, you'll also need

• 1x M3x10 screw
• 1x M3nS square nut

If you prefer, you can also split the spindle model yourself in the slicer and join it with a dowel.

To assemble, bolt the two pulleys together using the M3 screws and M3nN nuts, then tighten them down enough that the two halves won't move. If using the split spindle, push the M3nS into the slot and bolt that together as well. Press one of the bearings into the pulley assembly, insert the spindle, then add the other bearing on the other side - these should all be easy press fits. Screw the two wedges on to the spindle, with the flat side facing out; you might need to file the ends of the spindle a bit to deal with elephant's foot.

When printing, use a filament that'll be resistant to the temperatures you expect to run the dryer at. I recommend against PLA.

Installation

Remove the stock 4mm shafts and 624 bearings from the Space Pi. If you're using the 4mm rods, press those into the holes on the bottom of the stands - ensure the chamfers are on the outside. Snap both stands in place where the bearings were, then stick the spool holder into a filament spool and drop that into the stands with the wedges centered in them.

Your particular bearings may need the pulley pieces aligned differently, or the wedges screwed on looser or tighter than mine did. There's an amount of experimentation and tweaking involved here, but the unloaded assembly should spin freely for at least a second or two, and much longer if a full spool is loaded.

Use

To change the spool, just lift it out and swap the spool holder into a new one. The design accommodates common spool sizes, but you may need to remove the 4mm rods from the stands or design a different (larger) spindle for some brands of filament.

Customizaton

Spool doesn't fit over the pulley or the edge hits the shaft or case? Design your own! Check the 3rd image for the critical dimensions of a pulley half. If you'd like to bolt halves together, the bolt circle should be about 31mm in diameter, and you should leave 3mm of material at the bottom of the hole.

Changelog

2024-10-01: added an alternate set of parts to print the spindle in two halves and bolt them together

2025-02-28: added a 54mm pulley model which should fit cardboard spools, an image with the critical geometry for designing your own spools, and switched to using nylocks to bolt the pulley together