On Jul 7, 11:42 pm, woodworker88 wrote:
On Jul 6, 10:14 am, Ned Simmons wrote:

Hardinge specs the thread as 1.238-20 in the "Total Workholding"
catalog. You may find the relevant section here...http://www.hardinge.com/?pageId=141

Yeah, I thought it was something like that.

The thread OD on my collets measures from 1.220 - 1.230 for Enco to
~1.243 for R-S-B. I made a collet nut for an S&D drill grinding
fixture that fits closely on a 1.240 thread. Some of the R-S-B collets
are too tight for it.

How would you measure an inside thread to cut it to 1.238"? Cutting
out a fixed distance from the ID only works if the tip geometry is
correct and your lathe isn't worn. The spreadsheet gearbox chart I
made for my old South Bend gives the 29 degree infeed and tip width
based on Machinery's Handbook thread data but in practice the last few
thousandths are cut-and-try, mainly because I don't regrind the tip
for each pitch, especially the internal threading bit. It's about
right for 32TPI so it makes coarser pitches undersize if I zero the
compound on the blank's surface. If I understand the book correctly,
the flat should be 0.00625" wide for an internal 20TPI UN thread.

This is why I suggested using your largest collet thread as a GO
gauge.

Jim Wilkins