Spool Center Hub (parametric), 608 Bearing

UPDATE: 15 July 2024: added retention nubs to the press-fit axel so they fit the hub more snugly

UPDATE 13 August 2025: added a parametric file so you can create adapters for spools that aren't already included. There is only one option, and it is for the spool's hub diameter (what I call the the hole in the center of the spool the ‘hub’—it's not the correct term but it's easier to type). Enter a value between 45 and 100 mm, outside of these limits the design will break. Your custom sized adapter will fit the standard hubs (hex things that hold the bearings).

We all know that for best results, hydroscopic materials like TPU should be printed from a drybox. I like this cereal box adapter https://www.printables.com/model/835472-4l-cereal-filament-dry-box , but had issues with mounting the spool. I wanted to have the least possible resistance to the extruder pulling the filament and getting everything aligned so that there is no interference is crucial—but not easy to accomplish with the model's hub adapter. This design solves the issue by providing a hard mounting point. This is designed for spools with a 55 mm center opening… I have verified compatibility with Overture, Bambulab and Polymaker and other brands may work too, or they might not. LMK if there's a size you really need and I'll spin it up.

The model uses 2 608 sized skateboard bearings, they should be easily obtainable on line and at price points that vary depending on how “smoothly" they roll. I would try to avoid ones that are caked in grease—we don't like greasy fingers around printers.

A couple of notes. The adapter is printed in 2 parts (no supports): a hub and an axel. These are assembled via friction fit and as there are so many variables to getting an exact fit, you may need use a tool*** to encourage things into position—the default ‘correct’ position is where the axel is flush with the hub on the side that the bearing goes onto. If you have spools that are narrower, there should be some room to adjust how much the axel sticks out. I've provided a tool to assist with alignment and removal of the axel from the hub.

The bearings are intended to be press fit so they don't fall off and go rolling under the table. If they are too loose, a bit of one of those prime lines makes a dandy shim. There is a second plate that has a loser slip fit for the bearings, this can be handy if you want to keep a set of hubs on several spools and switch the bearings between them but yes indeed, they can fall off and roll under the table.

These adapters can be used for any other spool holder that is expecting a 608 bearing in the center of the spool (I haven't found any really, so looks like there's more design work for me… donor spool holder for respooling!)

*** Sage advice I got from the construction trades: 1. Use the right tool for the job. 2. The right tool is always a hammer. 3. Anything can be a hammer