Rewinding Spool Holder (inspired by Filamentalist)

Rewinding Spool Holder

When I first saw Filamentalist (https://github.com/Carrot-collective/ERCF_v2/tree/master/Recommended_Options/Filamentalist_Rewinder/Filamentalist_Classic_Rewinder) working, it was magical.

There was one big flaw in my opinion though: supporting filament spools, especially cardboard spools, on rollers can be unreliable if they are almost empty. So I took the Filamentalist idea and built a new design based on that idea, but with a central hub instead of rollers.

For the hub design, I took inspiration from Bambulab AMS Lite. It's intended to be a bit slippery, as the spool slips on the hub a little during rewinding if the filament-O-Ring friction is too high. The adjustment screw under the PTFE push fit is used to tweak the amount of grip on the filament.

I included number plates 1 through 5 to make the 5 spool holders for a Prusa MMU2/MMU3 easily identifyable.

Update 2025-11-11: new frame_mainplate.stl to allow adjusting gear tolerance (the middle gear can be moved by 2mm). Adjust so the gears run smoothly but keep the gap between the teeth to a minimum.

Bill of Materials

• 1x 8mm steel rod, at least 85mm long (I used 100mm to build mine)
• 1x HF081412 one way bearing
• 2x O-rings 3.5x20mm (20mm ID, 27mm OD)
• 1x ECAS pneumatic press fit
• 3x bearing type 608 (8mm ID, 22mm OD, 7mm thickness)
• 4x bearing type 625 (5mm ID, 16mm OD, 5mm thickness)
• 12x M5 nut DIN 934
• 2x M5 locking nut DIN 985
• 8x M5x20 DIN 912 (cylinder head) screw
• 1x M5x25 DIN 912 (cylinder head) screw
• 5x M5x35 DIN 912 (cylinder head) screw
• 1x M4 locking nut DIN 985
• 1x DIN125 washer (4.3mm ID, 9mm OD)
• 1x M4x20 DIN 912 (cylinder head) screw
• 6x M3 nut DIN 934
• 3x M3x10 ISO 7380 (button head) screw
• 3x M3x8 ISO 7380 (button head) screw

Printing

PETG and PLA should be fine. For a more duable spool holder, print the gears in something abrasion resistant. I used Iglidur 150, probably overkill for that task.

Some parts need supports. If you need a rewinding spool holder, you are not a beginner. Add supports where necessary for your printer.

I'm not sure if all parts are in the ideal print orientation. Use your own judgement to correct the orientation.

Assembly

General instructions

• (Almost) all screw heads and nuts have their recess where they fit into. Exceptions are the M5 locking nuts.
• All bearings have the correct sized hole they need to be pressed into. This does require some force.
• Depending on print quality, the gears can be a bit rough. You might have to tweak the seam and/or corners if your printer isn't tuned well enough or you use a more difficult filament for them. They have to mesh smoothly.

Spool Axle

• Using M3x8 screws and M3 nuts, connect 3x spoolaxle_spoke to spoolaxle_hub.
• Insert 625 bearing into spoolgear.
• Using M5x20 screws and M5 nuts, connect spoolaxle_hub to spoolgear. The screw heads sit flush in the spoolgear. If they don't, you might have it on backwards.
• Using M5x25 screw and M5 nut, connect spoolgear to mainplate, use photos as reference to see where it goes. You'll need the long end of an allen wrench to fiddle the screw in.

Middle Gear

• Insert 625 bearing into middlegear.
• Using M5x20 screw and M5 nut, connect middlegear to mainplate, use photos as reference to see where it goes.

Mainplate

• Mount rearfoot and frontfoot to the mainplate using M5x35 screws and M5 nuts. The angles on mainplate and the feet have to match, don't mount them reverse.
• Mount the driverarm to the frontfoot using M5x20 screws and M5 nuts.

Driver Assembly Preparation

• Insert the 608 bearings into mainplate (1x) and driverarm (2x).
• Insert the one way bearing into the driverwheel and pull the two O-rings on the driverwheel.
• Press the ECAS fitting into filamentclamp_R. This does need some force. Depending on your printer's quality, you might have to tweak the overhang parts of the print a little. It has to be a strong press fit though, don't take off too much material.
• Connect the two filamentclamps using an M3x10 screw and M3 nut.
• Mount the numberplate to the filamentclamps using M5x20 screw and M5 locking nut. The bend in the numberplate loosely matches the filamentclamps curve.
• Prepare the drivegear using 2x M3x10 screws and M3 nuts but don't screw them down yet

Driver Assembly

• Insert the 8mm shaft through the driverarm, holding the driverwheel with the one way bearing between the two driverarm bearings.
• Make sure the driverwheel can roll freely in the “filament off the spool” direction with a stationary shaft.
• Between driverarm and mainplate, first put the distancetube and then the drivegear on the shaft while continuing to push it through the bearings until it sits in the mainplate's bearing and the gears all mesh.
• Screw down the drivegear screws to lock the shaft in place.
• Mount the filamentclamps in the driverarm using M5x35 screw and M5 locking nut (yes I know, this could be prettier, I got lazy).
• Add the M4x20 screw with a washer through the front of the driverarm and through the filamentclamps. Put the M4 locking nut in the filamentclamps and twist it only a few turns so it does not fall off.

Tuning

Add a spool of filament, thread the end through the filamentclamps (there is a funnel where the filament should go into) and push/pull on the filament coming out of the ECAS fitting. Tighten the M4 screw until it properly rewinds but not much tighter, allowing for some slip between filament and rubber O-Rings.