On Feb 12, 1:50*pm, Mark Rand wrote:
On Tue, 12 Feb 2008 07:37:32 -0800 (PST), John Martin
wrote:



That said, I've never heard of a 7 TPI lead screw, and can't imagine
why you'd want one.

John Martin

Does it count that my BCA jig borer (actually an Excel Model "0" ) has got
14tpi leadscrews on both axes of the table?

In this case, someone installed 7/16" Whitworth screws, either when it was
made in the middle of WWII, or at some later date. They'll get replaced with
10 or 20tpi ACME ones when I rebuild it.

Mark Rand
RTFM

Yeah, it counts. Confusing, though - at least to me. On a lathe, you
can use about any pitch leadscrew you want and get the desired feed
through the change gears. On a screw used for positioning, though -
unless you've got some gears between the dial and the screw - you'd
have to be working in fourteenths (or some fraction thereof) of an
inch, no? Not in the usual thousandths. What is on the dials?

John Martin