Following a bit of diagnostic work on the latest lathe purchase, it looks like the SCR motor controller is the problem (motor runs smoothly when powered from a couple car batteries, but growls/rumbles when powered by the controller, and the controller is pulling far too many amps - pulling 5amps from the mains when only 1amp is going through the motor).

So, I've now got the option of either trying to locate a new motor controller suitable for powering a 0.55kw (3/4hp) 180V DC motor, or swapping the whole lot out for a normal AC motor and VFD.

The only suitable SCR controllers I've found so far are KB Electronics ones, with the KBCC-225 being the nearest match in terms of features. However, it's going to cost at least $200, and that will probably work out to nearer £200 by the time everybody else adds their fees/taxes.

And for £230 I can get a 1hp Marelli motor & Parker VFD delivered from here.