Trammel of Archimedes
28 December 2016
That looks like a fun one-day project. Google's woodworking workshop had a router bit with a 10° angle, which made the grooves easy to cut.
I used my lathe to create a nice knob, and cut the rest of the parts on the bandsaw. Once stained, everything was ready for assembly.
At first it was a bit rough, but rubbing candle wax on the slides made it run smoothly. A dot of epoxy on each screw keeps them from loosening. Below is a video of the mechanism in action.
With hindsight, there's one design defect. The whole thing is too large to hold comfortably. I should have made it smaller so that it fits more easily in a hand. An easy fix I'm considering is to drill four finger holes in the base so that it can be gripped from below, similar to a bowling ball.