Gunsmithing Threading ?

[ROLEXrifleman]

OK, don't rape me over this one but I'm out of my league when it comes to this and now that I'm in a CLASS 3 friendly state and I'm getting things together I'm looking for some knowledge.

Please go over with me what I think I know and correct me were I'm wrong.

using the size 1/2 x 28 for these next statements



A) the 1st number, 1/2, represents the MAJOR diameter of the threads. Meaning the absolute top of the threads measured exactly 180 degres from each other ( top and bottom for lack of a better term) in this case the measurment from the top to bottom is .500" or 1/2

B) the second number, 28, represents the actual thread COUNT and not the pitch as commonly said. in this example we would have 28 threads along a 1" run. Obviosly we are talking barrels so 28 threads per inch of barrel.

C) Based on the numbers given the actual thread pitch for a barrel threaded 1/2 x 28 is .0357

D) what thread form is used when threading firearm barrels?

E) The HAND of the thread would be the direction a bolt ( in our cases a flash hider or can) would have to be turned in order to TIGHTEN. generaly speaking this is a RH. Why are there some that use left? Simply to be diffrent? I understand that in some cases you need to use a LH twist because there are rotaional forces acting that would loosen the connection through use, but in suppresor use there are no rotational forces be used, simply linear that could cause the can to loosen, so why not be standardized? damn HK Mark 23

F) Minor diameter would be the actual diameter of the shaft left under the threads?

G) Pitch diameter, do we even need to care?

H) The number of starts, can I assume for what is being talked about here the answer is 1?

I have more questions but I guess we can start here.

as always TIA

 

[ROLEXrifleman]

Re: Threading ?

Also, is there a standard for thread depth? I know the formula for minor diamter is major - (depth x 2)

 

[300sniper]

Re: Threading ?

a) partially correct. there is still some tolerance with a class 3 thread. i'm showing a .4935-.5000 major diameter for a 1/2-28 class 3 external thread.

d)60*

g) the pitch diameter is critical if you are doing an external thread without the internal threaded part (suppressor, brake, flash hider ect.) to use as a gauge. if you want a true class 3 thread, three-wire gauges are the way to go. you need the thread pitch to calculate what your "over the wire" measurement will be.


everything else looks correct to me.

 

[300sniper]

Re: Threading ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ROLEXrifleman</div><div class="ubbcode-body">Also, is there a standard for thread depth? I know the formula for minor diamter is major - (depth x 2) </div></div>

for a sharp 60* v-thread, .866/threads per inch equals the thread depth. using your 1/2-28 for example: .866/28=.0309" thread depth.

 

[ROLEXrifleman]

Re: Threading ?

saying thank you doesnt begin to show my appreciation!

 

[wnroscoe]

Re: Threading ?

Wow Rolex, now I'm confused

All kidding aside, all "V" threads used by gunsmiths are 60 degrees; this angle is built into the tool. If turning down and threading for 1/2x28 simply turn your shank down anywhere from .495" to .499", it doesn’t matter. After your threading tool is set at the correct angle and center start threading. Make sure you indicated your barrel in by the bore and not the barrel OD. Baffle strikes will suck for accuracy.

The depth for 1/2x28 threads is .0309" or .031", this can be determined by the formula below and works with all threads.

1 / 28tpi = .0357" x .866" = .0309"

When the compound gets to about .020" to .025" deep check the threads for fit. If they don’t fit, great, that means you can keep threading taking small cuts (.001") as you go until the threads fit. At this point, check often (after each pass) unless you’re threading to a gauge use your job piece for the fit.

There are two different classes of threads commonly used by suppressor manufactures, Class 2 and Class 3. Within each class there is a standard for external threads, "A" and internal threads "B"

Class 2B and 3B have the same measurements while 2A and 3A are different. The only way to thread your muzzle to an industry standard is with the use of a ring go gauge. Threading to fit your suppressor won’t be an industry standard 2A or 3A and may not work from suppressor #1 to #2.

 

[wi50]

Re: Threading ?

I suppose someone will chew my ass or have a technical response but heres for us laymen. Maybe it helps you, mmaybe not.

You can figure your infeed on the lathe with the compound set at 30*, it doesn't matter what diameter the thread is, if it's 28 tpi, or 12 tpi.

Take 1 dovode by TPI X .750 and you will get verry close to.

For example 1 divided by 28, X .750 = .027 infeed on your compound dial.

It will get you verry close, but may vary depending on machine, tool, material. Cut a bit less and check for fit. Once I cut my calculated infeed, I'll then cut a few thousandths straight in on the cross slide untill my threads fit the particular part. When threading for something like a brake or suppressor, one manufacture may have a bit different thread depth than another so I'll typically leave a little more clearance than when cutting threads to mate with a specific part.

 

[bachelorjack]

Re: Threading ?

<span style="font-weight: bold">We send ALL of our threading to Jered at American Precision Arms.</span>

 

[300sniper]

Re: Threading ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BachelorJack</div><div class="ubbcode-body"><span style="font-weight: bold">We send ALL of our threading to Jered at American Precision Arms.</span>

</div></div>

way to answer a guy's questions.

 

[robpiat]

Re: Threading ?

There are some great PDF drawings from AAC pinned over at Silencertalk