Adjustable-width Compact Spool Auto Rewinder (Proof of Concept, Metal Spring, Sliding Clutch, for Drybox)

Spool auto rewinder with

• metal spring
• adjustable sliding clutch
• compact design placed within spool
• adjustable width for spools between 67 and 128 mm
• intended for the limited space within the (Un)original Prusa (Heated) Drybox

For spools with a hole diameter > 51 mm. Perfect for 1kg and 2kg Prusament.

It is based on the Compact Spool Auto-Rewinder and it's stronger version remix.

Disclaimer

Please consider this model as a proof-of-concept.

I am happy with the overall design, but it still might need some tweaking of tolerances and did only very limited testing.

As I am not sure how soon I will be able to fine-tune and finalize it, I've added the complete Fusion360 design file and strongly encourage your input and remixes.

If you have any questions, feel free to leave a comment. I am happy to provide additional details on (printing or assembly) upon request.

Additional Parts

Due to the splitted body and further miniturization of the mechanism, a single auto-rewinder requires 6x bearings 10x15x4 mm (6700 / 61700).

Printing

I printed it from PETG on MK4S with mainly the standard settings

• 0.2 mm (STRUCTURAL) for the outer body and stands
• 0.1 mm (FAST DETAIL) for the interior

25 % infill and one additional perimeter layer.

Several parts need “smart fill” supports on vertical overhangs.

I liked the idea of the MMU3 spool auto-rewinder for the (Un)original (heated) drybox, but wanted to improve upon

• printed spring → metal spring
• sliding clutch relying purely on gravity-induced friction between spool and rewinder body → sliding clutch with adjustable friction
• fixed width → width adjustable to different spool sizes

In search of an alternative, I found the Compact Spool Auto-Rewinder and it's stronger version remix. It already uses a metal spring, a adjustable sliding clutch and places the mechanism neatly within the spool's hole, but the total width was still fixed.

Having limited space in the drybox, I wanted the rewinder to occupy only as much space as absolutely necessary, while at the same time being flexible to hold 1kg and 2kg Prusament spools.

So I used the concept of the Stronger Auto-Rewinder, but split the axle and main body into two separate parts. This way my version is compatible with spools having a width between (roughly) 67 to 128 mm and a hole diameter of > 51 mm.