Tim Williams wrote:
I doubt you need a machine *anywhere* near as stiff as a metalworking lathe.
Just a slow turning, sealed spindle as far as I know. The only forces
present are bearings, the flame and pressure (plus or minus) inside the
glass, no? And the flame needn't be positioned within thousandths of the
glass surface either.

Nope.
I've used a couple of stepper motors duct-taped to a plank, for
joining a couple of tubes.
Worked just fine.