Digital screwcutting "gearbox"

Hi all,

I am sure that thius question has been asked and answered many times,
so apologies in advance if it is tedious. However...

I am interested in adding facilities to my Super 7 lathe to allow it to
cut threads using a stepper to drive the L/S, synchronised to the
headstock through a phase-locked loop. A side benefit should be
variable slow feeds and a "virtual saddle stop". I have worked out a
scheme to do this which I think will work but would like to see if I
can learn from others' experience first!

Can anyone please point me to material on the web, or elsewhere,
suggesting how this can be done, and/or other peoples' experiences of
doing it?

Cheers,

John Haine.