Auto-Rewind in a Cereal Drybox

Cereal container dryboxes are an elegant way to store filament. Auto-rewinders prevent tangles and eliminate the need for filament buffers. Porque no los dos? Space constraints.
 

@Jerrari's Auto-Rewind Spool Holder for RepRack demonstrates an auto-rewinding system where the coils are contained entirely in the roller, making them very compact. If we shrink these rollers length-wise, we can fit them into a cereal container, with limited compromise to rewinding force, all while preserving a convenient lid-on-top orientation.

Features

• Auto-rewinding rollers
• Desiccant box with snap-on lid
• Hygrometer holder (rectangular shape)
• Lid-on-top orientation
• Fits spools up to 200mm diameter and 65mm width (successfully tested with 1kg spools from Bambu Lab, Elegoo, Sunlu, AnyCubic, and generic brands)
• No-drill option available (print a replacement lid and screw in a PC4 fitting.

What you need

• 1 - Cereal Box Container - A specific mould, sold under brands like Wildone  or Skroam. It has three vertical indents and looks like this:
   

• 4x 608-2RS Bearings (2 per roller): (AliExpress, Amazon)
• 1x PC4-M10 or PC4-M6 Fitting: Your filament will feed through this connector. Either drill a hole in the container or print a replacement lid designed for screwing in the fitting. (AliExpress, Amazon / Amazon)
• Desiccant Beads: (Amazon)
• (Optional) Hygrometer: (Amazon)

Assembly

Because the container tapers, two differently sized rollers are provided - one short and one long. Print one of each.

Refer to Jerrari's chill instructional video, skipping the frame assembly. The original model page also has offers instructions and additional details.

The main bracket should be placed in the container such that the hygrometer is as far as it will go toward the wide end. A vertical guide will ensure the short roller axle is positioned snugly between the two outer-most grip indents. Both rollers should spin freely.
 

Clutch 22
 
Jerrari added a clutch option for the final gear of the coils. Using the normal final gear, the rollers will stop rotating once they fully coil, at which point the spool will slide against them. In the clutch version, the coils unfurl when a tension threshold is reached, allowing the roller to continuously rotate. Both versions of the final gear are included among the model files.

I prefer the non-clutch final gear. The clutch frequently fails to receive enough tension to unfurl, and when it does, the unfurling is noisy. You may have a different experience, and performance of the clutch will vary depending on the material and weight of the spool, the material of the roller, and the direction the filament is pulled from. Jerrari recommends using Plasti Dip on the roller shell for added grip. 

(Left: normal final gear  Right: clutch final gear with insert)

Credit
 

Many thanks to Jerrari for his fantastic auto-rewind roller design.

Change Log

v1.1 - May 1, 2025

• Updated the body model: Removed the horizontal guides above the small roller (the little bumps next to the axle entrance). They were causing more harm than good for cardboard spools at the 65mm width limit.