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