I too will dig the spare speedo from its slumbers & have a play. Firstly I’ll have to calibrate the lath, which runs on three phase, controlled by a inverter drive, to that end I’ll have to find some reflective opto switches (or reed switches), then I’ll have to rag an old calculator & link the 1 & + to a circuit with two optos & an off circuit to another. Then arrange them around the chuck having made an adapter for the speedo drive.
OH shit you do it & I’ll just watch ! !