Barrel threading question?

[mark5pt56]

So, I'm not a machinist, but I understand a few things in regards to how things work and why something is made a certain way, etc.. This pertains to when one would screw on a tuner, this case an ATS and you have to use the spacer and maybe another smaller one so the threads of the tuner will stay on the barrel threads. When a barrel is threaded is there a reason why there's such a large gap between the ends of the threads and the barrel shoulder? My guess is the cutter is a certain width and one is unable to run the threads closer to the shoulder? If that's not it, why is it?

 

[spife7980]

That’s exactly it, you can’t get minor to full thread depth all the way to the shoulder so you turn down that last bit clear so it doesn’t jam the threads stopped before the shoulder faces come into contact.

 

[mark5pt56]

Okie, thank you. Having said that, I do wish some would get closer if possible, have had a couple to where I had to use the provided shim and another from the Dead Air shim kit.

 

[DeathBeforeDismount]

Buy a lathe take a few years of schooling so you can see how easy it is. If you want good solid cuts you need to use big solid work holding, which doesn't always play well with making cuts in small spaces. You can buy or make shims from just about anywhere including McMaster carr. It's really a non issie.

 

[mark5pt56]

Buy a lathe take a few years of schooling so you can see how easy it is. If you want good solid cuts you need to use big solid work holding, which doesn't always play well with making cuts in small spaces. You can buy or make shims from just about anywhere including McMaster carr. It's really a non issie.

Ok, look--I was asking a question to make sure I understood the why, not criticizing anyone or saying the job was easy. I have seen a slight difference in the gap, hence asking, guess it may be a difference in the equipment. I'll leave it at that for now.

 

[jhoyda]

Ok, look--I was asking a question to make sure I understood the why, not criticizing anyone or saying the job was easy. I have seen a slight difference in the gap, hence asking, guess it may be a difference in the equipment. I'll leave it at that for now.

The ignore feature is most useful on this website.

 

[spife7980]

Ok, look--I was asking a question to make sure I understood the why, not criticizing anyone or saying the job was easy. I have seen a slight difference in the gap, hence asking, guess it may be a difference in the equipment. I'll leave it at that for now.

Most specs call for .060 of undercut clearance in the 1/2x28 or 5/8x24 threads.

If we take an inch and divide it by 28 we get .035” and by 24 we get .042” so the specs are calling out about 1.5-2x the thread revolutions.

Can’t speak to the ats tuner and how much of a spacer it may need

 

[FredHammer]

That’s exactly it, you can’t get minor to full thread depth all the way to the shoulder so you turn down that last bit clear so it doesn’t jam the threads stopped before the shoulder faces come into contact.

Had a friend send me a pic of a threaded muzzle with the threads leading all the up to the shoulder. I hadn't seen that yet on a muzzle thread job and was told the guy was a machinist that would dabble in some barrel work. I was under the understanding the space between shoulder was exactly for the reason you stated above. So, how did this particular machinist get the threads all the way to the shoulder? Some hand threading device? I sent off a pic resend of the muzzle in question.

ETA Pic:

 

[LeftyJason]

Speaking as a cnc machinist with lot of years cutting threads.

First view this video. Not mine. BTW finding a short video of cnc thread cutting with out a thread clearance is hard.


That thread insert is a single point type non topping. This shows a topping insert.

Either type the absolute closest you can get the insert to a shoulder is 1/2 thread+ a little clearance. That last thread will not be full either because of the thread retract. That is best case scenario.

If you are machining these threads on a manual non cnc lathe you need the thread pull out if if you are threading conventionally to stop the lathe in time. Or you can start in the cutout with your tool upside down and thread backwards. Or use an ID threader on the backside spinning reverse.

 

[spife7980]

Had a friend send me a pic of a threaded muzzle with the threads leading all the up to the shoulder. I hadn't seen that yet on a muzzle thread job and was told the guy was a machinist that would dabble in some barrel work. I was under the understanding the space between shoulder was exactly for the reason you stated above. So, how did this particular machinist get the threads all the way to the shoulder? Some hand threading device? I sent off a pic resend of the muzzle in question.

ETA Pic:
View attachment 8448189

That looks pretty shitty to me and its relying on the female thread to have a clearance cut around otherwise it will jam up before the shoulder faces come into contact. Which many muzzle device manufacturers do just so they dont have to answer a phone call where a bad thread is ultimately to blame. Its easy to use a 1/16 parting tool to clean up the barrel thread for zero issue insurance.

 

[LeftyJason]

Had a friend send me a pic of a threaded muzzle with the threads leading all the up to the shoulder. I hadn't seen that yet on a muzzle thread job and was told the guy was a machinist that would dabble in some barrel work. I was under the understanding the space between shoulder was exactly for the reason you stated above. So, how did this particular machinist get the threads all the way to the shoulder? Some hand threading device? I sent off a pic resend of the muzzle in question.

ETA Pic:
View attachment 8448189

What does the thread look like on the other side? Where the thread goes shallow at the bottom is where it will start to have issues.

 

[FredHammer]

That looks pretty shitty to me and its relying on the female thread to have a clearance cut around otherwise it will jam up before the shoulder faces come into contact. Which many muzzle device manufacturers do just so they dont have to answer a phone call where a bad thread is ultimately to blame. Its easy to use a 1/16 parting tool to clean up the barrel thread for zero issue insurance.
View attachment 8448228

Ok, this would explain why he says the muzzle brake fits fine.

 

[FredHammer]

What does the thread look like on the other side? Where the thread goes shallow at the bottom is where it will start to have issues.

Don't know, only pic I got and he has a brake on it now.