All Hardinge HLV and HLV-H variants feature a continuously variable speed drive to the spindle. It starts with a 3-phase, two speed squirrel cage induction motor, rated at 500 rpm and 1500 rpm nominal (less in practice, due to slip) at 50 Hz. This would be 600 rpm and 1800 rpm at 60 Hz.
Depicted here, are two external rotor, polyphase, electronic commutation motors, fitted to custom mounting plates, ready to be installed in disk recording systems, to control the leadscrew.
These are very high precision motors, with features allowing accurate, closed-loop control of speed over a wide range, as well as positioning applications. A combination of hall sensor arrays and high resolution encoders makes them extremely versatile, compatible with a wide range of lathes.
Back in 2015, we started a big lathe project, taking a beat-up Fairchild lathe from the 1930's, fitting it with an RCA cutter head, and eventually going full-on with a stereophonic feedback cutter head, vacuum clamp-down platter and automatically variable pitch.