Nicely done indeed, both in the design and execution.
A couple questions as an EE who had to learn a bit of machining to build my projects.
1) I have been under the impression that lapping compound and the like should be kept far away from the lathe and mill and other precision tools as you don't want specks of the lapping grit to wind up in places where it shouldn't. That didn't seem to bother you much. I keep my bench grinder, for instance, 30 feet or so from the lathe and mill. What's the real story?
2) Over time, will the ball-to-carbon fiber surface become work polished and hence not develop enough friction to hold the arms in place? Or is that expected and the solution is to tighten the plates to increase pressure between the plates and ball surface?