I was looking for an auto-rewind spoolholder that fits inside the common cereal box dryboxes. It rewinds your filament on unload with a MMU und makes using buffers obsolete.
Most of the existing designs use external springs or weights and don't fit inside the hub and cereal boxes. Also the printed spring designs didn't work well for me and they don't have a proper clutch/freehub mechanism. The clutch is friction based and never has a well defined slipping threshold.
This isn't actually a remix, it's a completely new design with a different mechanism. It uses common household rubber / elastic bands and a lead screw.
Features:
- Very slim designs, fits inside the spool hub with no extra space needed. Therefore it can be used in any kind of drybox and with any kind of spoolholder.
- Clutch / freehub. It rewinds a defined number of revolutions (ca. 1,5 by default) and then disengages.
- Reverse freehub. It can be further rewinded by hand.
- Torque can be easily adjusted by rubber band length and tension
- Optional lockout lever can be installed to use the spoolholder/hub with no rewind function and no additional drag / completey free spinning
- Quick print, less material usage and no support required.
Of course there are also some disadvanteges:
- Auto-Rewinding is currently limited to about 1,5 revolutions, that's about 90cm with a full spool. The screw design (pitch) could propably be changed to achieve more, but I have not tested it.
- The freehub mechanism is noisy.
- The current design is very narrow to make it fit inside dryboxes. the Hub Body is 80mm and the axle is 90mm in width. Because of that it doesn't fit wide spools. Max width is probably around 70-75mm.
BOM:
- 2x 608 bearing
- 2x household elastic rubber bands
- 2x 15mm piece of filament
- 2x 5mm piece of ptfe tube
PRINT:
- PETG recommended.
- 3 Walls, 0.2 layer, 15% infill. Optionally 0.1 for the screw and sledge.
- no supports
- good bed adhesion and brim required for printing the screw (standing upright)
- the files are not oriented for printing, slicer auto orientation works well
- your printer should be well calibrated.
ASSEMBLY:
- Insert the printed springs into the pockets of the bottom and top hub shells. They should clip in so they don't fall out . Otherwise use a drop of hot glue to fix them. The printed springs are used only for the reverse freehub.
- Install pieces of 15mm filament and 5mm ptfe tube to the bottom shell. Make sure to use the correct length, they act as a bearing and should be able to spin. Also make sure that the ptfe sits in its pocket.
- Fix the rubber bands to the sledge and put the sledge onto the screw, than install the 608 bearings and put the screw into the bottom shell.
- Carefully route the rubber bands around the ptfe bearing as shown in the pictures. You can play with different lengths and tension. The rubber band should barely be tensioned when in the relaxed position. Longer bands usually give a more linear tension and torque. Press the rubber band into the grove so it can't get pitched between the bottom and top shells in the next step.
- Carefully snap the bottom and top shells together. Make sure the rubber bands don't get pinched anywhere. Also make sure that the filament pieces find their counterpart holes in the top shell.
- Mount your filament spool and center it using the caps.
- Slide the axle of the spoolhub into the bracket from the top.
Additional Notes:
- There is an addional “ScrewShort” part. This replaces the normal “Screw” and reduces the rewinding turns to around 1 turn. I use this because 1 turn is sufficient for me.
- The provided “Bracket” can be glued directly to the inside of a cereal drybox (Fits the common ones on Amazon). Otherwise you can remix this part to use the hub with whatever spoolholder you like.
- The lockout levers are optional. When the spool is removed you can insert them into the slots on both sides from the outside to disable the rewinding machanism and use your spoolholder like a normal free spinning one.
- The hub shells contain multiple sub-parts for the lettering. You can use it to print the lettering with MMU in a different color, but you don't have to.
- You can grease the screw and sledge for lower friction and wear.
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