Magnetic Rewind Attachment, with Dessicant Compartment for Polydryer (and similar dryboxes)

A system I put together to be able to rewind my spools after changing filament, without opening the box. I used Polydryer boxes, and thread length is sized to fit the width of the box, but it'd probably work in anything similar with the spool rolling on its rim. Optionally, the center can be packed with extra desiccant. The ventilated plug/cap is meant to be turned with a coin.

The FreeCAD/fcstd file included requires the ThreadProfile addon. It is parameterized to allow easy customization of the following:

• Magnet diameter, thickness
• Magnet Count (I found 10 was about right for the N52 1/4"x1/4" magnets I used)
• Main thread diameter (I suggest 25+mm for strength, and 40+mm if adding desiccant)
• Thread pitches and tolerance
• Overall length (For fitting other dryboxes)
• Clamping plate cone diameters and thickness (Match to the spool it is being installed in)
• Coin diameter and thickness (For the slot in the desiccant plug)

The file is pretty unwieldy due to all of the threaded parts, so I suggest disabling automatic recompute while editing the parameter sheet. Also specify mm when entering dimensions into the sheet.

When installing the magnets, I suggest alternating orientation so you don't have to worry about matching the magnets on the knob and spool side. It is for this reason I also suggest an even number of magnets.

Finally, on all of my Polydryer boxes, I've noticed that the metal tubes used as rollers have sharp edges that dig into the walls, adding a lot of friction. I suggest either polishing the ends, or printing a small disk (~7mm diameter, ≤0.4mm thick) to cover up them up. There are (probably) also more extensive modifications out there that would be even better.