Some people are dumb on threads

LeftyJason

Thumbnail-les
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Bought this gun "factory new" and might should've sent it back but I did get it for $100 cheaper. No idea who threaded it originally. Planned on sending it to @LongRifles Inc. before I got it anyway.

Internet pic. Forgot to take my own.
1253135.png

Thread shoulder looks like crap and doesn't feel completely smooth. Burrs on threads.
20200327_233655.jpg20200327_233726.jpg
But the biggest problem is the thread pitch.
20200327_234101.jpg
Why the heck would anybody ever thread a gun muzzle 1/2-20?
 

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stevieb92

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I've never heard of a suppressor threaded for 1/2-20, but my guess is it was done by someone not familiar with suppressors. That thread is commonly available in a standard tap and die kit. It's a standard bolt fine thread, but not the extra fine 1/2-28. Have it cut off and re-threaded for 1/2-28.
 

LeftyJason

Thumbnail-les
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I've never heard of a suppressor threaded for 1/2-20, but my guess is it was done by someone not familiar with suppressors. That thread is commonly available in a standard tap and die kit. It's a standard bolt fine thread, but not the extra fine 1/2-28. Have it cut off and re-threaded for 1/2-28.
That's why I'm sending it off to Long Rifles. Also because I had a local smith quote me $180 just for threading.
 
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hlee

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I inherited a 300 weatherby mag with 9/16-32 threads. People do weird things...
 
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Tiger_Shilone

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As all ready stated, most suppressed pellet rifles that are not metric threaded have 1/2-20 threads as do some european rimfires. CZ and Anschutz sell 1/2-28 threaded rifles in the USA but sell 1/2-20 elsewhere.

Those are pretty crappy threads, not cutting fast enough at improper SFM gives threads like those. SS is a bitch though, soft metal (depending on heat treat) that work hardens on the surface quickly.
 
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LeftyJason

Thumbnail-les
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As all ready stated, most suppressed pellet rifles that are not metric threaded have 1/2-20 threads as do some european rimfires. CZ and Anschutz sell 1/2-28 threaded rifles in the USA but sell 1/2-20 elsewhere.

Those are pretty crappy threads, not cutting fast enough at improper SFM gives threads like those. SS is a bitch though, soft metal (depending on heat treat) that work hardens on the surface quickly.
Im a cnc machinist myself. I once had to cut tapered double shouldered buttress threads in 0.5 inch walled aluminum pipe 3" dia 30' long. Limited to 200rpm because any faster was scary.

I've cut quite a bit of stainless myself as well on lathes. At work I grind threads in inconel along with other grinding. I work with 15-5, 17-4, inconel, Udimet, and Mar-m-247. Not a stranger to threads.
 

Tiger_Shilone

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30' 3" pipe, wow. Sounds like an oil rig set-up, seen those guys chase damaged threads in a HAAS TL-3 in the field with what looked like 15' unsupported spinning out the backside with a 3' diameter whip swinging around. I was in awe and nervous as hell at the same time.

Titanium is another one that surface work hardens quickly while machining it. Most of our stuff is one or two one-off job shop type repairs or prototypes in mild steels or aluminum alloys. Don't use the exotic materials too much and we always have to go look up what the insert chip loads need to change to for them to cut successfully. Proper insert coatings help too, but we are pretty limited to what we have on hand usually.

Back to the threads, LRI has some great machine porn vids that he has posted here. Got to love all the custom fixtures he has for his CNC's.
 
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Sniff

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1/2x20 has been the most common thread for .22 calibre in the UK and New Zealand forever.

I've got at least six.22s and two .223s threaded 1/2x20 and only one, a S&W MP15, in 1/2x28.
 
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TACC

Gunny Sergeant
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Thete is no way to salvage what has been done on that correct? They have to literally cut off that and start over correct?
 

LeftyJason

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Thete is no way to salvage what has been done on that correct? They have to literally cut off that and start over correct?
Yes. Threads are the same size. I can stand a barrel that is half an inch shorter.

To understand threads here is a basic blueprint.
082711_0213_Understandi20.jpg
Say you have a 1/2-28 3a thread.

All 1/2 inch threads have the same basic major diameter.
Pitch length is dependant on the threads per inch (the - 28). In this case it is 1÷28=. 035714.
The 3a means the class of fit as in how loose it is. Controlled by pitch diameter. You look it up for whatever thread you are cutting. Thread classes go from 1-3, a for external, b for internal. 1 are the loosest, 3 the tightest.

Here is the Thunderbeast arms print for rimfire threads.
TBAC_Rimfire_Thread_Guide.jpg
It specifies the thread fit (3a) and the pitch diameter (dimension b).

If my original nasty thread was cut correctly its pitch diameter should've been 0.4643-0.4675 for a 3a thread.