I've always wondered why,when threading for a smallring mauser you make a relief cut in the barrel when you could relieve the threads in the reciever and not cut away barrel. Wouldnt it leave you with more strengh in the chamber area then the relief cut in the barrel?

Mauser barrel shanks have a relief cut so that they're easier to thread--no other reason that I know of. This small relief causes no issue in reqards to strengh but you could do as you suggest if you wanted.

The releif does not need to be large, and it is very difficult (impossible) to stop the threading in the EXACT spot on a rotating barrel. WIthout the relief, the tool would hit the shoulder of the barrel. With the relief cut to any decent size, you have no degredation of strength.

Even if you releived the female threads on the action, you would still have thread to a shoulder, requiring a relief groove.

Given the geometry of the relief grrove and the 55°Whitworth threads, I imaging the relief is stronger and less prone to faliure any way. If cut properly, there would be a lesser stress riser there than at the bottoms of the threads. So actually you are making the barrel better by cutting a relief.

But this is all only applicable on paper any way and has no bearing on the real world. I have never heard of a barrel letting go at the bottom of a thread or relief groove. If you had pressures that high, something else would give first. And the same goes for high or low cycle fatigue.

With or without the relief groove the strength of the tenon is only as strong as the diameter of the minor diameter of the thread. It makes no difference in strength.

If an action does not have the threads relieved, then you have to cut a relief groove. If you are using a recoil lug, or the action threads are relieved, the you don't need to cut a groove. Threading to a shoulder without a groove is done every day, I do it all the time.

I thread to a shoulder without a groove. I don't thread at 300RPM either. I was just taught this way many years ago. The groove hurts nothing though.
Butch

If you are careful and know what you're doing it is possible to thread to the shoulder as Butch said. But, if you must have a relief groove, cut it on the barrel not the receiver. The barrel is an expendable part, the receiver isn't. JMHO

Ray

Ray is correct.
Butch

Most all of the custom actions I encounter have the action relieved.

Cutting right up to the shoulder, even when pulling the belt by hand to drive the lathe really slow, is something that I've never been able to master. I've ground special bits with only half the form on the left side, but can't get right up flush against the shoulder. I sure would like to have someone who has mastered the art, either show me or describe how it's done.
Until then, I guess I'll continue to cut a relief groove.

Relieving the action and not cutting the groove in the barrel allows the barrel to be set back, if needed in the future.

A doubtful advantage in a hunting rifle, in my opinion.

quote:

Originally posted by ron vella:
Cutting right up to the shoulder, even when pulling the belt by hand to drive the lathe really slow, is something that I've never been able to master. I've ground special bits with only half the form on the left side, but can't get right up flush against the shoulder. I sure would like to have someone who has mastered the art, either show me or describe how it's done.
Until then, I guess I'll continue to cut a relief groove.

While I haven't mastered it myself, not that I would care to, I am proficient at withdrawing a tool at the precise minute to avoid a problem.

To do by hand you would need a very slow rpm, a good dial indicator, a foot brake, perfect timing and a quick reflex.

I would imagine you would bring your specially ground threading tool or insert to the shoulder, set your dial idicator to zero, with a 1 revolution lead, and use your foot brake to stop the machine at exactly the right time.

While being able to thread to the shoulder sounds good on paper, in practice, I would think it borders on the insane.

I am not a gunsmith, just a machinist making down hole oilfield tools. We ALWAYS thread up to the shoulder without a run out groove on the pin. From an engeering standpoint I really don't think it makes a difference but try telling that to a company man when your tool string comes up with a broken off tool at the pin. It's the difference between a $300. an hour wireline job or a $5000. an hour rig job.
All day long I thread at 300rpm to 500rpm as close as .010 to .030 from the shoulder. When you first start doing it your sweating bullets but now after 15 years I couldn't do it any other way. It's also faster cutting the relief in the box instead of the pin, time is money.
Some of the big hole Lehman's have an air kickout that is made especially for this.
I can even thread up to the shoulder while cutting metric threads when you have to reverse the machine and keep it in lead, although I'll only do this on a Leblond with a round on and off switch.
So my point is don't be scared of this, just get some scrap material turn up the rpm's, get a topping off insert and get after it. {Just don't try the 4tpi in the beginning.}

I saw an article by Steve Acker, I think it may be in his book, which shows a rig he designed that attaches to the spindle on his lathe so he can turn threads by hand and get right to the shoulder. I haven't had a need for it.

I thread to the shoulder, or at least close to it, with a dial indicator showing the stop point. What's the big deal anyway? The Mausers all have a relief on the inside anyway.

quote:

Originally posted by Toomany Tools:
I saw an article by Steve Acker, I think it may be in his book, which shows a rig he designed that attaches to the spindle on his lathe so he can turn threads by hand and get right to the shoulder. I haven't had a need for it.

I saw that and I did that.
I have a crank for my big lathe.
When cutting threads, don't turn the crank backwards without backing out the cross feed, the backlash in the cartridge feed will break off the tool tip.

Really big lathes are too wide to reach around. I sometimes turn the chuck by hand. By the time the threads are cut, I have a blister on my hand

quote:

Originally posted by Jim Kobe:
I thread to the shoulder, or at least close to it, with a dial indicator showing the stop point. What's the big deal anyway? The Mausers all have a relief on the inside anyway.

Ever try to recess the receiver?.....it's a lot easier said than accomplished!

I have pulled Mauser barrels with a "relief groove" as wide as a quarter of the tenon. I don't think that is needed. One should really have more than three full threads holding a barrel.

I believe it is practical to thread to within 1/2 of a thread width of the shoulder if using the traditional single point tool. Remember this cuts only with the advancing edge. That leading edge can be brought up to the shoulder, but the minor diameter of the thread will be at least 1/2 a thread away. If the face of the receiver is cut square, it may not draw up tight. I try to never take that much off the receiver, I just do a very very light squaring cut. That leaves enough relief in most mauser receivers to tighten up a barrel with threads cut almost up to the shoulder, no large relief cut is needed. Because I don't do this often, it also allows me to "adjust" if I later cut a chamber too deep.

Roger

The standard thread relief groove is 1.5 times the pitch wide cut to the minor diameter.

Pulling the tool out at the shoulder is easy with a little practice. I am convinced that most gunsmiths never thread enough to get really proficient at threading.
The 700 Remington barrels I have examined appeared to have been threaded with multichaser head like a Geometric or similar head that pops open at a stop. The 40X Remington barrels that I have examined have been threaded single point and the tool pulled out.

The old 1923 model Pratt & Whitney tool room lathe that I learned to thread on had two cross slides ...one inside the other. When threading, the inner slide was locked to the outer and the outer was unlocked from the carriage. The outer slide had a high helix nut that turned in against a stop. When pulling the tool out at a shoulder the high helix nut retracted the cross slides about 2 inches for one full turn of the dial.

Somewhere along the way I also ran an engine lathe that had an kickout on the carriage. It worked fine if you were threading to a thread relief groove.

quote:

Originally posted by ireload2:


The old 1923 model Pratt & Whitney tool room lathe that I learned to thread on had two cross slides ...one inside the other. When threading, the inner slide was locked to the outer and the outer was unlocked from the carriage. The outer slide had a high helix nut that turned in against a stop. When pulling the tool out at a shoulder the high helix nut retracted the cross slides about 2 inches for one full turn of the dial.

Yikes, that's like reading patents.