Predictably, after getting my little metal lathe, I spent the next few weeks getting to know the machine and trying to make some useful projects.
I played around with metal pen designs, using some UNI refills from the office store and working out dimensions from there. They have a screw-in plug for the top to extend/retract the tip, and various combinations of knurling or hex grips, and various proportions of aluminum or brass.
The spinning tops are brass with an aluminum handle and a 1/4" ball bearing for the base. I got that part of the design from one of the online top sellers and adapted it to the stock I had. For all of these (and the pens) i was mostly winging it other than a couple of fussy dimensions, so they're all a bit different.
The tops spin really well, since they're made on a lathe and fairly concentric, and have some weight from the brass. At one point i had 12 of them all spinning at the same time, and they go long enough i could probably spin twice as many before the first one stopped.
After that i tried a different challenge and made myself a scribe that uses old steel phonograph needles for the scribe point. The needles are hard steel, and i probably already have a lifetime supply from even the limited listening i do on my acoustic phonographs.
It's really just a single-size pin vise, with an aluminum collet modeled after the one in Dremel tools, but the depth limited to seat a phonograph needle with a usable amount of stick-out. There's a storage compartment in the top closed off with a screw cap that holds several more needles for replaceable tips, or to store the tip for transport.