Hi Greg,
My ISP has had recent problems with their news server, which has caused me
to miss several posts. I read your inquiry through Google, however, which
I have copied below:

I have a few unhardened HRS studs with 1/4-20 LH threads on the end,
which I didn't turn down enough- they're big enough that they won't
fit in the holes I just threaded with a proper tap- the OD is not
unreasonable, but the threads aren't deep enough. Otherwise the studs
are fine, so I'd like to deepen the thread by maybe 3 to 5 thousanths
or so. I've tried re-chucking and threading a little more, but its
really hard to get everything set right and the consequences are a
wrecked thread.

Since its just a couple studs that need help, I was thinking I might
be able to build a cheapie die (avoiding paying McMaster's highway
robbery for such things) by drilling & tapping a short length of 1"
diameter stock, then slitting it to provide relief for the
swarf/chip/turnings (I still don't know the difference..)- and
hardening so the sharp edge of the slit will last long enough. Maybe
I could run the slit in at something less than perpindicular to the
tangent of the stock to give the edge a bit of rake. Maybe I could
also be clever and slightly ream the end of the hole to introduce the
edge more gradually.

Would this work, or is there a better approach?

Thanks,

Gregm

Hi Greg,

Studs have what is known in the industry as a class 5 interference fit
thread, which is intended to be a force fit in the mating part. The
government has published manuals on threads in which this subject is well
discussed. They are (or at least were) known as the Screw Thread Standards
For Federal Services H28 Handbook.

It is documented in the handbook that studs should NOT bottom out on the end
of the thread, but instead be the force fit mentioned. According to H28,
a much higher incidence of failure is attributed to studs that are tightened
against the end of the thread. I would assume that studs are generally
heat treated and lend themselves to the force fit installation, so in your
case it may not apply.

Did I manage to add yet another layer of confusion? (Hope not!)

Good luck

Harold