On Feb 11, 9:49*pm, Jon Elson wrote:
Bruno wrote:
A friend just got a Birmingham 12x36 lathe and tells me the leadscrew
is 8 TPI, yet the thread dial gear is 14 teeth, with 8 marks on it.
Anyone else out there with a similar lathe? Does it have the same
thread dial? *I would think a 16 tooth thread dial would be
appropriate. What's the thinking behind 14, and will it really work?

Have him get a magnifier and count again. *It is IMPOSSIBLE that
a lathe was built with a 14-T threading dial gear, unless the
guy who sold it to him is well known for practical jokes!

I'd expect if 2 teeth were missing, he'd clearly notice.

Jon

Nothing is impossible, although it of course would not work. Could a
manufacturer have gotten some 14 tooth gears mixed in with the 16's?
Maybe....

It is possible that the guy doesn't know how to count thread pitch,
and is including the first AND last thread in his count. Sort of like
saw teeth, where a handsaw of 8 points and 7 teeth per inch is the
same thing.

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

John Martin