"Ken Sterling" wrote in message
s.com...

"DoN. Nichols" wrote in message
...
snip-------
And after all -- the pitch diameter is what really matters.
Hence the measuring over wires.

Enjoy,
DoN.


Yep, my point, exactly. All the rest does is cloud the issue. None of
it
is close enough to use for proper threading.

Harold


Points well taken, but in this particular situation, I'm threading
5/16-40, internal, 3/16 deep to a solid bottom. Don't know any
way to check this so just wanted to get the numbers as close as I can.
Thanks.
Ken.


In a case such as this, what I've done is turn my own plug gage. By using
(proper) wires and cutting the thread to proper form you can enjoy
considerable success, although the gage is subject to change, so it is good
for only a minimum amount of use. It's a good idea to use something like
O6 tool steel (Graph-Mo, for example), which tends to leave a better finish
than carbon steel. A leaded steel might be a good choice for a very small
amount of usage. It is also critical to have the use of a comparator, or
at least good magnification, so the proper amount of flat can be ground on
the threading tool, which, in the case of such a fine thread, is very
slight. If the thread in question is critical (such as having to pass
inspection) the chance of hitting the proper pitch diameter by trusting the
compound movement would be very small due to the minimal tolerance, although
certainly possible. The problem is you don't really have any idea if the
thread being generated is where you think it is, so it's very easy to stop
at the proper number on the dial and be off, either too large or too small
on the pitch diameter.

Hope this helps, Ken. It's not intended to give you a bad time.

Good luck!

Harold