How are the barrel threads cut in an action?

[boltfluter]

It is!
Watched a action get thread milled at a manufacturer here in Washington, plus they do a cool start of the thread with no half thread and a really robust lead in like you see on fire hose threads.
Really cool process.

Not 100% but I believe that is called a "higby cut".
Paul

 

[Alex Wheeler]

Some single point, some thread mill, and some still finish with a tap. Threads are not super critical in my opinion.

 

[SKWERLZ]

Not 100% but I believe that is called a "higby cut".
Paul

Yea!

That’s what it is.

 

[jackieschmidt]

Some single point, some thread mill, and some still finish with a tap. Threads are not super critical in my opinion.

As long as they are truly straight and square with the bolt way and action face.

 

[Dusty Stevens]

As long as they are truly straight and square with the bolt way and action face.

As long as theyre loose enough the action face, which is straight with the raceway, can put the barrel straight. They dont have to be very straight at all in reality

 

[Alex Wheeler]

As long as they are truly straight and square with the bolt way and action face.

Opinions will vary here. I have measured out hundreds of actions. One with the threads and action face that are truly square to the bolt way is quite rare. In my opinion thats not too important. So long as the lugs seat and threads are loose enough to allow the barrel to shoulder without bind I have not been able to correlate accuracy to action straightness.

 

[jackieschmidt]

Opinions will vary here. I have measured out hundreds of actions. One with the threads and action face that are truly square to the bolt way is quite rare. In my opinion thats not too important. So long as the lugs seat and threads are loose enough to allow the barrel to shoulder without bind I have not been able to correlate accuracy to action straightness.

I don’t disagree with you and Dusty often, but on this one, I have to take exception.
if you tighten threads against an unsquare surface, the threads will no longer have an equal load in the radial direction. Sure, you will compress or distort a fractional amount of the material on the V’s that contact first, but for things to be truly correct, the threads and that the action face should indeed be truly square with each other.
With me , it’s a machinist thing.
In the long run, does it make any difference on the target. Probably not. But……..

 

[Alex Wheeler]

I don’t disagree with you and Dusty often, but on this one, I have to take exception.
if you tighten threads against an unsquare surface, the threads will no longer have an equal load in the radial direction. Sure, you will compress or distort a fractional amount of the material on the V’s that contact first, but for things to be truly correct, the threads and that the action face should indeed be truly square with each other.
With me , it’s a machinist thing.
In the long run, does it make any difference on the target. Probably not. But……..

Im not arguing that at all. Im just saying it doesnt show up on target.

 

[Dusty Stevens]

I don’t disagree with you and Dusty often, but on this one, I have to take exception.
if you tighten threads against an unsquare surface, the threads will no longer have an equal load in the radial direction. Sure, you will compress or distort a fractional amount of the material on the V’s that contact first, but for things to be truly correct, the threads and that the action face should indeed be truly square with each other.
With me , it’s a machinist thing.
In the long run, does it make any difference on the target. Probably not. But……..

Im thinking if the shoulder is straight it will align the barrel to the shoulder, which is straight once im done, (action and barrel), then i feel as long as the threads are loose enough to not influence that pull up the shoulders are what hold it straight. Thats why i dont like a watertight thread on a barrel, i let the shoulders dictate the pullup. As long as its got the wobble to mate up the threads being straight is irrelevant to that joint. Just my opinion of course. In all my machining days and all the hundreds of hours of fastener schools i went to for turbine bolting i have never wanted the threads to make or break the joint. Very few of the threads on a threaded joint actually do anything anyway. And if we were going by real engineering standards a tenon would be over 2” long too!

 

[BoydAllen]

I have an early Stiller Viper action, which like the Panda has an aluminum body with a steel insert for the lug seats and tenon threads. Back then the inserts were thread milled with an intentional taper to distribute the load farther back from the action face. Later, I understand that the method of threading was changed and to eliminate possible confusion by smiths, the taper was eliminated. The taper was designed to be paired with an untapered tenon cut so that it had enough clearance for the smaller thread diameter toward the rear of the action. It is my understanding that because of tenon stretch as it is tightened, with parallel action and tenon threads, that most of the load is on the first three threads. Harold Vaughn discusses this subject extensively in his book "Rifle Accuracy Facts" in which action thread taper is given as one way to distribute the load.

 

[jackieschmidt]

I have an early Stiller Viper action, which like the Panda has an aluminum body with a steel insert for the lug seats and tenon threads. Back then the inserts were thread milled with an intentional taper to distribute the load farther back from the action face. Later, I understand that the method of threading was changed and to eliminate possible confusion by smiths, the taper was eliminated. The taper was designed to be paired with an untapered tenon cut so that it had enough clearance for the smaller thread diameter toward the rear of the action. It is my understanding that because of tenon stretch as it is tightened, with parallel action and tenon threads, that most of the load is on the first three threads. Harold Vaughn discusses this subject extensively in his book "Rifle Accuracy Facts" in which action thread taper is given as one way to distribute the load.

We are talking two different things. A tapered thread is still truly straight with what ever mating surface it seats against. A crooked thread is still crooked regardless.

In my opinion, seating a true thread against a crooked face is no different than seating a crooked thread against a true face. Either will place an uneven load on the joint.

 

[Walt Krafft]

I know of no way to directly measure concentricity or straightness of a thread. If you can't inspect it, the only way to control it is through good machining practice when you make it. Then, allow the assembled parts some wiggle room to align themselves.

 

[BoydAllen]

We are talking two different things. A tapered thread is still truly straight with what ever mating surface it seats against. A crooked thread is still crooked regardless.

In my opinion, seating a true thread against a crooked face is no different than seating a crooked thread against a true face. Either will place an uneven load on the joint.

Yes, I admit I did get off topic.

 

[jackieschmidt]

I know of no way to directly measure concentricity or straightness of a thread. If you can't inspect it, the only way to control it is through good machining practice when you make it. Then, allow the assembled parts some wiggle room to align themselves.

historically, the one positive way to insure any two separate surfaces are truly straight, (or square) with each other is machining them on the same setup. In theory, the only discrepancy that can arise is the accuracy built into the machine.

Bat Machine has a great video where they take the viewer from every step in the manufacture of their actions. Bruce has a way of explaining things In a down to earth manner. In the video at about minute 13:40, he speaks of the importance of machining the thread at that particular time in the process to insure it is true with the body and boltway before the piece is removed from the machine, BUT, …….does not mention facing it.

As a machinist, that caught my attention. Maybe they do face it at that time as well, but he didn’t say it and emphasize the importance of insuring those two surfaces do indeed run perfectly true and square with each other.

 

[Jud96]

Single point threaded on a CNC lathe with carbine inserts during the same operation the face, bore, and lug recesses are machined.