Conversion of 12 x 24 lathe

Hello,

A friend of mine, having seen my conversion of a Sherline lathe and
the parts it makes, has decided that he really needs to convert his
much bigger lathe. It's a Chinese made, gear head lathe (less than a
year old), which can swing parts 12 inches in diameter. He wants to
turn model locomotive wheels on it which are cast iron and 10 inches
or 7 inches diameter. The lathe can be seen here http://www.warco.co
uk/lathes/gh1224.htm

Backlash has already been considered and various modifications have
been either made or planned to correct problems.

How do we determine the right size stepper motor for this two-axis
conversion?

Presumably, the best choice would be to run the steppers through a
belt-reduction drive to increase the torque available?

I can't convince him that once he's converted his machine to CNC he
might not want to run it manually, but if he insists, are there any
strategies that might permit this?

Thanks for your advice,

Mike Jones
Cardiff, Wales