"Tim Wescott" wrote in message
news
On Tue, 03 Apr 2012 14:29:35 -0400, Wild_Bill wrote:

This calculator offers numerous options to suit several different
lathes.

Interesting, but wouldn't work with my Smithy, which has a gearbox
between the change gears and the lead screw (said gearbox having a
fast/
slow lever that changes the ratio by 2:1).

The gearing isn't that difficult to figure out. If the spindle and
leadscrew turn at the same speed, the lathe will copy the leadscrew's
pitch. For other pitches the cut-thread-to-leadscrew ratio equals the
gear ratio.

jsw