UPDATE: 2 (3 actually) really key bits: Added hex shafts so things can actually turn on it, and added a little snap-y thing so that when closed the balls won't fall out. The snap bit is a little big, I filed it down, but as I only need one I didn't bother tweaking the file.

I needed a thrust bearing type thing for the gyro/pendulum/hamster in my Lego BB-8.

I had bought a small bearing, but decided it wouldn't work, and I have some 1/4" Acetal balls lying around, so I decided to make an upper & lower race for them.

It's hard to see this at work, so I made a video of them spinning: https://youtu.be/8dvflMZPUWg, and another which doesn't help much: https://youtu.be/s5WQSzcg234 - feel free to visit the advertisers to support my things :)

The load is intended to be over the balls. Loads on the end of the upper ring will cause it to rub on the bottom. The bottom race's inner wall is lower and the upper race's outer wall is shorter. My thinking is that maybe the balls get shoved to the outside and the top gets shoved toward the center. Not sure if that actually happens though, may have needed more oval of a cross section for that.

You'll need about 19 Acetal (Delrin) 1/4" bearings. The race is slightly larger which worked well for me with my printer error, however you may need to scale it slightly (very slightly). You don't want the race completely packed with bearings, 18 or 19 is probably good.

I bought bearings from McMaster-Carr