Cursitor Doom wrote:
On Wed, 16 Jul 2014 17:52:32 +0100, "harryagain"
wrote:

They are quite common on new cheap lathes for example, saves having a
gearbox.

But how would you do screwcutting and whatnot if you can't change the
speed of the saddle independently of the chuck? I can't see any way of
avoiding a gearbox (or a set of changewheels) in such circumstances.

Sorry CD - this is just more Harry ********!

Cheap lathes have brush motor with drill speed type pulse width
modulation speed controllers.
They do away with having geared heads in this was but still have
standard changewheels for screwcutting.

There is quite a lot of work going on under the amateur electronic
leadscrew project where the leadscrew is driven by a stepper motor but
electronically synchronised with the lathe mandrel for a near infinite
range of screw cutting pitches. proper CNC lathes have nearly always
done it this way but I digress!