An idler pulley that goes on ball bearings, roughly compatible with the ones that come with Shapeoko.
I wanted to go with a dual-drive on the Y axis, but that required sourcing a second set of idlers (and inventables is out of stock). Luckily, the part isn't that tough to model from scratch. Sized for 16mm OD bearings (size 625) on a 5mm shaft.
2x 625ZZ bearings
1x M5 bolt (length depending on application)
1x shim washer
- Print, making sure the thin portion gets 2 shells
- Build your bearing-washer-bearing sandwich
- Insert sandwich into idler part. It should be snug, but not enough to require a hammer.
If you have to deform the print to insert the bearing, increase clearance parameter and try again. I've tried with -ZZ and -RS bearings, and both of them need a little bit of loading before they turn instead of the bearing turning on the bolt. If your bolts are undersized, a layer of masking tape may help.