Threading and thread measuring question

[seanb]

I have to cut a 5/8-24 thread on a gun barrel for customer. Thread class is 2A I am threading with a full profile insert.


I have the thread cut to the major diameter spec 0.6238-0.6166 but the pitch is undersize at 0.56508.


Now I don't have to meet any certain spec, but I am threading for a suppressor and I want to make sure the customer doesn't have a baffle strike.

So do I need to recut the thread?


And what is the thread pitch I am measuring with the 3 wires.

I don't have the quick detach flash suppressor that the silencer threads onto to test with.

 

[ridgeway]

Did you dial in the bore with a DTI before cutting and threading the tenon? If so, the tenon will be concentric to the bore. Therefore, you should not have any issues with clearance. As for thread fit, I prefer to have the piece I'm fitting so I can cut the threads and fit by feel. Sorry I can't be any assistance number wise.

 

[rangerman]

What do you mean by " the pitch is undersize at 0.56508 " ?

You said you wanted to make a 5/8 - 24 thread so the pitch should be 1/24" or .0417" .

 

[09kevin]

I think Sean is talking about the pitch diameter.

Kevin

 

[tripletap3]

I have ran into this several times especially when I don’t have the item that I am threading on the barrel. I always push the person to provide me with what they want to thread the muzzle for but sometimes I get the "I’m not sure yet" response. I don't try to get a super tight fit to the item anyway, because the person can/will change their mind and will want to use some other muzzle device that doesn’t fit. I personally find that having a accurate and square shoulder for the device to seat up against is what is most important for alignment. I have a collection of “high quality” dies in all the popular muzzle thread sizes just for this occasion.

 

[GK1918]

simply put, the customer can not provide the example, such as the female thread, take it some where else. Im not being wise, but I have to know
all aspects with what I am working with, so no lawyer fellow comes after me, especially with fire arms, and when you have a couple thousand miles
of thread cutting under your belt, you dont need wires and all that written stuff 'that says you have to do". Its like --does one have to look at the floor board to find your brake and gas pedal and read the math for stepping on the brake? So why should a 5/8 24 thread turn into a Nasa project?

supose i'll get the thumbs down, but I'm the owner of the shop.
samuel

 

[Ray C]

In every situation like this that I've ever encountered, thread class and fit are, of-course important factors -but... the shoulder lockup (be it square or tapered) is by far, the predominant concern that dictates practical success or failure.

In any event, by definition, the thread is cut too deep if your Pd is 5651. I have a feeling the depth might have been cut without taking into consideration the flat top of the crest.

If you calculate the theoretical depth of the thread, you need to cut to that depth relative to the major OD before flattening off the crests to the allowed widths as shown in this calculator.

Go here and plugin 5/8-24 UNEF external. http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx



Ray

 

[Bill Gruby]

If you are saying "Pitch" Crest of one thread to crest of next thread is .56508 you should have cut the barrel right off during the threading operation. As stated earlier the "Pitch" for that thread is only .0417.

"Billy G"

 

[Tony Wells]

Once you say "5/8-24 2A" then yes, you are cutting to a certain specification. It should be safe to assume that you received that in an instruction either from the customer, or as a mating part spec from the attachment you intend to fit up. There are ring gages available that will give you a go/no-go evaluation of some of the features, most particularly the pitch diameter. Each feature of the thread has controls determined by the "2A" you gave. I don't generally favor topping inserts for UN threads. Some people believe that you should just cut until they top, and the thread should be good. Maybe, maybe not.

Using thread wires isn't the simplest thing to learn. They are as accurate as the user, though. If your PD is truly that much under, then technically, you have scrapped the thread. The mating part will rattle on. Not acceptable. You've not much choice but to cut off the bad threads and try again, unless you have length constraints.

I believe I would try a couple of times on a piece of scrap to perfect the method before working on a customer's piece.

 

[seanb]

If you are saying "Pitch" Crest of one thread to crest of next thread is .56508 you should have cut the barrel right off during the threading operation. As stated earlier the "Pitch" for that thread is only .0417.

"Billy G"

Sorry I meant pitch diameter