On Tue, 12 Feb 2008 13:38:01 -0800 (PST), John Martin
wrote:

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

That's the problem. One dial is 0-100. The other dial is 0-100-0-100 (eg.
0-200). Not very useful really :-(

I'd like to have had a talk with the chap that did it and seen what was in his
mind. Possibly with the aid of an auger bit...


Mark Rand
RTFM