Auto-Rewind Spool Holder for Modular Drybox

Description

Now that I have a multi-color kit installed on my printer, I needed an auto-rewinder for my cereal container dryboxes in order to be able to keep my filament protected while printing and still reduce tangles on unloading.

After dropping some earlier efforts to add some escapement mechanism, the functionality actually came across fairly quickly, due in large part to the various other designs people have made with their descriptions of their process.

Printing

Settings

These are designed with 0.2mm layers in mind, with supports enabled. The springs need to be printed in PETG for better performance and lifetimes.

STEP vs STL

I've included .step files because they give smoother results with smaller files as long as your slicer (such as Orca Slicer) supports them. The .stl versions are included for those who need them for their workflows, but are normally of a poorer quality due to tessellation being baked in.

Springs

I was originally going to start with some ID card lanyard springs since I bought a larger pack of them back when I wanted one to use for a cable lift for my original Ender 3. Since I could not quickly find which box I had packed those up into, I went for the PETG spring route.

There are three different sets you can choose from. They differ in the number of "starts" each has: 1, 2 or 3. I've been defaulting to 2, but the others might work for your situations and needs.

Multi-color

Default versions have cut-outs for marks, but for multi-material printers you can either use the include "*_mmu.step" files or the stl versions with explicitly including the corresponding "*Marks.stl" file.

For multi-color printing, either choose Cap.stl + CapMarks.stl or Cap_mmu.step, and then Cover.stl + CoverMarks.stl or Cover_mmu.step. If you use the *_mmu.step files, you'll need to paint the marks the proper filament color. The nut files also have multi-color options available.

Parts Needed

For a complete hub you will need to print

• 1 cap

• 1 cover

• 1 drum

• 1 selector

• 1 selector disc

• 1 shaft

for springs:

• 2 SpringA

• 2 SpringB

• 1 SpringLock

helper tools:

• wrench A and or B, used for adjusting the tension

additional hardware

• 2 standard 608 skateboard bearings

Post-Print

• lining up the center pieces, fit one of spring A into spring B and gently push together until they seat. Repeat for the other set of spring A and spring B

• push on A/B spring pair down onto the spring lock (with the notched hole in the center) until they seat

• push the second A/B pair down onto the first until it seats

• push the drum on to the top of the springs assembly until it seats

• push one 608 bearing into the bottom of the cover piece

• slide the shaft from the inside of the cover into the bearing at the bottom. The squared end should extend fully from the bearing

• slide the spring assembly down onto the shaft, with the notched lock spring going in first

• gently push the selector down into the larger opening side of the cap, with the three legs lined up near the end of the internal spring arms where they end in the knobs. They should push the spring arms in as they go then lock into place with their tops peeking out the other side of the cap

• rotate the selector away from the ends of the spring arms, fully towards the "-" end of the slot. The wrench with three slots can help work these into place

• gently push down the selector disc onto the top of the cap, lining up with the three extruding ends of the selector. If needed, a small drop of glue can help hold the selector disc to the selector, but be sure not to get either glued to the cap itself. Note that the selector disc is optional, and can be left off

• firmly push the cap down onto the drum until it makes its way against the internal spring arms and the threads meet. Screw it firmly into the cover

• push the second 608 bearing down on the top of the shaft, fully into the opening on the cap

• screw one of the nuts partially onto the assembled hub unit

• lower the spool down onto the hub

• screw the other nut onto the hub, then screw both evenly until they tightly hold the spool in place, centered on the hub unit

• fit the two mount pieces into the side arms of the drybox

• paying attention to the direction arrows on the bottom of the cover, fit one end of the shaft into one side

• lower the other side of the drybox assembly down onto the remaining end of the shaft.

Once all pieces are in place, adjust the tension of the hub until it starts to slip only after at least half a revolution, and closer to tight enough to prevent slipping, but not tight enough to cause the filament to be hard to draw.

After getting the tension right, feed the filament out of the box and up through the normal printer's loading mechanism.

Usage

Once tension is adjusted, the hub should allow printing as normal, and then when the printer backs filament up it should keep just enough tension to pull it back in and not leave coils around.