Square Threads

H

Harry Bonar

New member
Sirs:
Doc and I were doing a 495 A-Square - I was helping him.
I had the bbl. tennon at .800, the tennon minor dia, cut and started threading 10 TPI! Everything looked fine - then, at the proper time we started the bbl. on#R@R$TT^%&&^*%&&. Visibly, the first thread was wider! Well, my threading tool had worked fine before but this steel was HARD!
My first thread, instead of being .050 wide was .075!!!!! %%$%#$##^#.
Yes, we corrected it and it worked great. I immediately made a new stiffer tool and AOK!
I won't mention the other mistakes we made on this project - no one would ever listen to me again! But, we've got this cannon feeding now and all is well - KEEP THOSE SQUARE CUTTING BITS SHORT AND STIFF AND .050-.052 WIDE!:o
Harry B.
 
Mr. Bonar, pardon me if I did not comprehend your answer, but if you cut the minor diameter to .800, your major diameter should have been .900. If you cut the minor diameter first, you will make no thread. Whereas, if your major diameter was .800, your minor diameter should have been .700 for a 10 t.p.i. square thread.
 
Harry,

I remember, when I first got drawings for the Garand, being surprised to discover the thread was not a sloppy square, but actually was an Acme thread. Moreover, the pitch diameter isn't in the vertical thread center, so the the intersects of the thread sides don't, at mid tolerance, have the same width at the minor and major diameters. I don't know if it is at all germane to what you were dealing with, but I'll put up a picture of the Garand thread specification for the curious?

garandthreadsde4.gif
 
Last edited:
Happy it worked out for you!

I might have practiced on a piece of stock before risking the barrel itself.

The first threads I ever single-pointed, nearly 30 years ago, were something on the order of 1.5” X 2TPI internal ACMEs ~4” deep in nickel-aluminum-bronze… first day on the job. I was sweating bullets and with the little bit of experience I had at the time, I literally engaged the nut and pulled the chuck around by hand…. Foreman came by later and said “nice threads, tomorrow I'll have a job that'll challenge you". :eek:

The Mori-Seiki I did it on became my personal buddy and I’ve never run a finer engine lathe.
 
square threads

Sirs:
I didn't give up, found under magnification I'd ground my tool wrong. Junked it and made a new one, "VERY CAREFULLY"!
Chucked a piece up, turned tennon to 1.125 dia. length .800 and got perfect threads with no play right into P-17!!!
There were two problems with my first tool, it was old, and it was oversize slightly and CUT like an ACME!
Nick, thanks for the drawing - I'll remember that! Thanks for the constructive help. I'm 72 now, need two frpont teeth pulled, a plate made, and was helping Doc buile his 495 A-Square, plus a different set of glasses!!

We shot the 495 A-Square twice each and let me tell you - it is a boomer. :D
No, my wife didn't knock my two teeth out - Sourdough hard pretzels!
Harry B.
 
SRG

Sir:
Sorry if I confused you. The tennon length is .800
on the P-17, major thd. dia is 1.125 and minor dia is just how you want thread depth to match action threads. I made a mistake in my tool being old - Sorry, but I do know how to cut square threads - if you have somes "tricks" up your sleeve please let me know - I can always learn something.:)
Sorry for the misunderstanding - I'm an old fart!
Harry B.
 
Last edited:
You must log in or register to reply here.
Back
Top