Threading help please

[Huub Buis]

In general if wall thickness is a problem I turn 0.5 mm pitch thread.
The threading depth depends on the tool geometry. If you have a sharp self ground HSS tool, you need to thread deeper than if you use an insert with the correct tool nose radius.
You can measure outer threads "easy" with the 3 wire method. Any 3 equal size wires (drills) will do if they are not to large or to small. If you turn the outer thread first than you can use that to verify your inner thread.
If you have a threading table that lists a 0.5 mm thread (M3) than you can use those values to calculate the values for other thread diameters that have the same pitch. For an M10 thread, just add 7 mm to the given dimensions.
The machinist handbook and this web site have a lot of size information. Beware that the cutting depths given are for threading tools that have the correct tool nose radius.

 

[redgrouse]

Presumably this is the exit cap of the suppressor holding the baffles in place ? Why not use 40tpi thus saving 0.10" per side on thread depth so this would leave a wall thickness very close to 0.025" -- similar solution to the M24 x 1.0 but imperial.
Is there any reason why you are using 1.0" OD or could it be larger ? Most 22cal suppressors are larger and most use 1/2" UNF thread on the barrel

 

[Investigator]

Presumably this is the exit cap of the suppressor holding the baffles in place ? Why not use 40tpi thus saving 0.10" per side on thread depth so this would leave a wall thickness very close to 0.025" -- similar solution to the M24 x 1.0 but imperial.
Is there any reason why you are using 1.0" OD or could it be larger ? Most 22cal suppressors are larger and most use 1/2" UNF thread on the barrel

Well, it's the mount endcap. threaded 1/2-28 to mount on the barrel. The diameter is pretty standard for rimfire suppressors. I'm not worried about the wall thickness at the root of the threads, there is plenty therefor the pressure it will hold.

 

[RandyWilson]

I’m blown away, where do you guys get these numbers from ? Machinists handbook?

It's a fluke of 60 degree threads @ 75% that the drill diameter is the major diameter minus the tread spacing. Examples would be a M6x1.0 would use a 5mm drill. M8x1.25 would use a 6.75 drill. This the same technique RJ did above where he used your 28 tpi to get 1/28 (0.036).

 

[tobnpr]

Ya know, there's a gunsmithing subforum under the weapons forum...
No reason to be cryptic describing what you're doing as threading a "rod" and a "tube", assuming you're doing this legally.
Machining tolerances are extremely tight for suppressors to maintain precise concentricity for obvious reasons.
It's oversimplification. I'm a smith, and I've read your posts several times and I'm still not clear on exactly what it is you're trying to do.

This is a direct-thread suppressor, on a Form 1 that has been approved?

 

[Investigator]

Really wasn't trying to be cryptic or hide anything. I'm making a form 1 rimfire suppressor, never tried to hide it. But the fact is I'm working on a tube. It will eventually become a suppressor tube, but right now it a 1" tube from online metals. The rod is likewise a 1" rod also from online metals. When I'm done, the rod will yield caps for the tube. Call it a suppressor tube, silencer tube, 6" tube, round tube, it's still a tube.

 

[Parlo]

Use metric to do the calcs in your head. If you have to use imperial try to use the pitch instead of the tpi. Knowing the tpi is only a figure to calculate the useful figure - the pitch.

 

[tobnpr]

Really wasn't trying to be cryptic or hide anything. I'm making a form 1 rimfire suppressor, never tried to hide it. But the fact is I'm working on a tube. It will eventually become a suppressor tube, but right now it a 1" tube from online metals. The rod is likewise a 1" rod also from online metals. When I'm done, the rod will yield caps for the tube. Call it a suppressor tube, silencer tube, 6" tube, round tube, it's still a tube.

OK, I'm "sort of " tracking- but still confused.
So your barrel is 1" OD with a 1/2"-28t muzzle (?).
I've never seen a factory muzzle threaded like that, so I'm assuming you did that profile yourself- but no idea why?
Did you cut the muzzle threads as Class 2, or 3? This determines the minor diameter of the male threads- which corresponds to what you'll need for the minor of the female threads for the mount. Easy enough to look up these numbers in the Machinery's Handbook based on the class of thread.

I am unclear as to how you plan to index this mount.
.050 shown on your drawing at the base of the mount is not enough meat to properly index the mount on the muzzle.
Why not use solid stock for the endcap instead of thin-wall tubing, drilled/bored/threaded for the 1/2", to seat/align on the muzzle shoulder?

 

[Investigator]

OK, I'm "sort of " tracking- but still confused.
So your barrel is 1" OD with a 1/2"-28t muzzle (?).
I've never seen a factory muzzle threaded like that, so I'm assuming you did that profile yourself- but no idea why?
Did you cut the muzzle threads as Class 2, or 3? This determines the minor diameter of the male threads- which corresponds to what you'll need for the minor of the female threads for the mount. Easy enough to look up these numbers in the Machinery's Handbook based on the class of thread.

I am unclear as to how you plan to index this mount.
.050 shown on your drawing at the base of the mount is not enough meat to properly index the mount on the muzzle.
Why not use solid stock for the endcap instead of thin-wall tubing, drilled/bored/threaded for the 1/2", to seat/align on the muzzle shoulder?

I'm unclear on what you are unclear about, not trying to be thick or make a joke, I just don't understand.
Let me start over.
You may be confused about the barrel, in this scenario there isn't one. The only 3 parts in this discussion are a suppressor tube which is 1" OD, and 2 endcaps for the suppressor. One of them will have a an exit hole for the bullet and will be threaded into the tube. The other endcap will be threaded externally to the tube, and will have internal threads of 1/2-28tpi to thread onto the industry standard threads for barrels.
Because it's easy, and I had no reason to change, setting the lathe up for 28tpi one time is why all the threads are 28tpi. There are other considerations for the thread choices but 28tpi seems to cover them all.

Edited to add: I'm not sure what you think I'm trying to index. I just need a 1" tube threaded with internal threads on each end, to which endcaps will be threaded into.

 

[Investigator]

Maybe this will help explain: This is not my pic, just one I found with a quick search on the internet, but this shows the 3 parts im making: