The subject seems to have shifted from polishing with diamond to making faceting machines.
if I was to build a new mast and faceting head assembly from scratch I would base it on Robert Slaters.
https://www.jrobertslater.com/homebuilt-faceting-machine/
His machine is easier to make than mine and the digital angle encoder he has on it is a huge plus and something I want.
But for the moment I’m busy making a concave cutting attachment, so the angle encoder will have to wait.