Quote Originally Posted by claytume
Donald..........never seen or heard of these.........anywhere on the net I can see one?
They're the simplest form of CNC for a lathe -- look at threading setups for Taig or Sherline lathes, neither of which have change gears available to do traditional thread cutting. In their simplest form, they use an optical encoder on the spindle, and each spindle pulse is converted to some set number of lead screw stepper steps, giving a set amount of advance per revolution. Using an encoding wheel with enough teeth, combined with the response time and inertia of the stepper system, gives smooth motion.

Start here.