I want to have some barrels threaded for use with suppressors, and the reputations of gunsmiths here in Vegas are mediocre at best.

Is there some sort of tool for checking that the muzzle threads are concentric to the bore?

George

More wise men will chime in, but checking concentricity of threads to any surface is problematic. A cap with internal threads, known to be concentric to the outside diameter would be the only tool my meager brain can think of...then the OD could be checked against the bore.

Depth mic and a gauge pin will get you plenty close enough

I think it's called using a reputable gunsmith that you trust... in the first place.

Ask the GS how he will do the threading; if he mentions a die, and not a lathe, then run away fast. Now, roughing with a lathe and cleaning up with a die might be ok. With any kind of good lathe skill, it is hard to do it wrong unless you are a real hack. Checking it after it is done is too late.

I had a guy in the shop just last week who blew his can off a new Savage with one shot. He wanted the same thing. The only thing I could think of was to thread a cap in the lathe then thread a stub also in the lathe, fit the cap to the stud and turn the OD to be concentric with the internal thread, put it on the client barrel, set it up using a pin gauge to dial in the bore, screw the cap on the barrel And check it with a dial indicator to check concentricity.

Lots of F'ing around and he didn't want to pay my hourly rate

Right; I just assume that the caps are already concentric with the cans. If not, then you will know with the first shot.
And so far, they have been machined well by the can maker.

You can make a gadget and charge him $150 to check it. Then, when you find out that it's non-concentric, you can chop off the old thread, re-cut the center in the muzzle with a piloted center cutting reamer, cut a new thread between centers and charge him another $150. (USA to CAD exchange is .30% so adjust accordingly)

OR !

Pull off the barrel, chop off the old thread, re-cut the center in the muzzle with a piloted center cutting reamer, cut a new thread between centers, charge him $150 and send him on his merry way.

It boils down to how much you like or dislike that particular customer, but Occam's razor always applies.

Or... since what you really want to know is if the can is concentric with the bore, why not set the barrel up in the lathe ( through the headstock, ),center the bore, then screw the can on and indicate the bore of the can? No special doo- dads, etc., and tells you what you need to know.

If the barrelled action or just barrel is setup correctly in the lathe to turn true with live centre support then you can't really go wrong in getting the thread concentric if cut with the lathe tool, not a die.
Suppressors for 22 RF rifles screw onto the 1/2" x 1/2" 20NF thread tight to the shoulder at end of thread. The thread should be cut on the snug side and with the suppressor screwed up tight to the square shoulder on the muzzle a spin up in the lathe will tell you immediately if you have got everything concentric.

For larger calibres the thread is usually cut so the suppressor, which is usually an over barrel type, will spin on easily and tighten on the taper of the barrel close to the stock forend tip to form a gas seal.

Got my sons Weatherby Vanguard 7mm-08 here at the moment with a suppressor on board; barrel shortened a couple of inches and can slides over barrel for approximately 3-4" before contacting the 1/2' 20NF thread then tightens up snug on the barrel taper.

Unless you really butcher everything it is impossible to not get these concentric, again a spin up in the lathe will show good the job is.

If your gunsmith keeps on getting it wrong I guess you will end up with 12" barrel and shortened stock forend

One easy way to check is screw on you muzzle device place a long rod that is a close fit to bore size into the barrel.

One should see if the rod is closer to one side of the device or the other.

If the treads are really off the rod well be touching the muzzle device.

Geeez.....all you need is a uni-mic and gauge pin clamped within the foot of the uni-mic

quote:

Originally posted by ted thorn:
Geeez.....all you need is a uni-mic and gauge pin clamped within the foot of the uni-mic

The deviation that you are looking for is mostly lineal, not axial. Plus, most people in this industry don't use full form carbide tooling so relying on the tops of the threads which people have crested with a file, if any of these coconuts bother to crest at all, is probably a fools venture. To get any sort of an accurate analysis you have to get your numbers from the flanks of the threads. That means that you have to cut a standard to measure from. You could use the device you intend to screw on. In doing that you are just assuming that the threads on the device are even remotely true and square and that the hole is even close to being in the middle. That's another crap shoot. I have had people bring me brakes to screw on and I always run them on a standard before installing them. Quite often they run out and flop around like a broken leg on a cat.

The threads are checked using the bore dia as the swing point.......gage pin via the anvil of the uni-mic claml and a small pin gage to hit the C/L of the barrel threads.

Take 3 or 4 quick spot checks and you will know the bore C/L vs the thread tangent

It wouldn't take 5 minutes

Well, If your can is 8 inches long and it's out .010 inch at the end. .010 inch divided by 8 is .00125 inch deviation per inch. Now, your thread extension is 1/2 inch long, so .00125 inch divided by two equals .000625 inch to look for. Or, if you went from thread to thread on 28 TPI you would be hunting for .00004464 inch deviation per thread. Thems mighty thin numbers. You would be wanting to make sure you had ZERO, play in the pin in your barrel or you could be chasing shadows. But I guess if one were to squint REALLY HARD, you might be able to get some sort of hard numbers!

Thin, mighty fawking thin! When I start looking for 1/2 thousandths of an inch I get a bad case of the heebby-jeebbys. But I'm kinda funny that way.

I am an end user, not a gunsmith. I don't trust any of the local yokels due to the horror stories I've heard from folks here.

I guess I'll have to send them off to be done.

George

Send it to Tom. If he screws it up, we'll pass out ugly sticks and have a good, old fashioned caning! I haven't been to a caning in a LONG time. They're a hit with the kiddies too and fun for the whole damned family. he he

quote:

Originally posted by speerchucker30x378:


Well, If your can is 8 inches long and it's out .010 inch at the end. .010 inch divided by 8 is .00125 inch deviation per inch. Now, your thread extension is 1/2 inch long, so .00125 inch divided by two equals .000625 inch to look for. Or, if you went from thread to thread on 28 TPI you would be hunting for .00004464 inch deviation per thread. Thems mighty thin numbers. You would be wanting to make sure you had ZERO, play in the pin in your barrel or you could be chasing shadows. But I guess if one were to squint REALLY HARD, you might be able to get some sort of hard numbers!

Thin, mighty fawking thin! When I start looking for 1/2 thousandths of an inch I get a bad case of the heebby-jeebbys. But I'm kinda funny that way.

.0005 would be a nice break

I can only wish

quote:

Originally posted by GeorgeS:
I want to have some barrels threaded for use with suppressors, and the reputations of gunsmiths here in Vegas are mediocre at best.

Is there some sort of tool for checking that the muzzle threads are concentric to the bore?

George

George, A quick visual check off the lathe
There should be NO drag on the thread. The mod will locate against the shoulder.finger tight. Look through the bbl when it's fitted you should see a clear round hole at the end of your mod.The mod bore will be 1 mm + on the rifle calibre.

If being done on a barrelled action then the easiest way is to chuck the action in the headstock with a mandrel of four jaw chuck and put the muzzle in a live centre.

that was the threads are concentric with the bore at the end where it counts.

A collar can then be turned to recrown if wished.

Not a very big job over here, have a look at this series of videos:

https://www.youtube.com/watch?v=HJyNiQax4eQ

quote:

Originally posted by GeorgeS:
I want to have some barrels threaded for use with suppressors, and the reputations of gunsmiths here in Vegas are mediocre at best.

Is there some sort of tool for checking that the muzzle threads are concentric to the bore?

George

Many ways to check concentricity to the bore as pointed out by a few here. But the real deal is checking after it's threaded is to late. I'd advise you spend the money and take your work to a shop that does proper work.

$150 for muzzle threads, if charged that i'd never thread a barrel, But yet I don't have overhead to pay for an a full time job to subsidize the garage hobby. I charge $50 to turn and thread a barrel i can just pop off the action, More if sights and gas blocks are in my way, $75 to cut crown and thread, I can have a guy in and out in an hour or less, and i doo use full profile carbide inserts, those little expensive buggers are worth their weight in gold. Far better finish and when you do your calculations on thread depth on the compound wow look at that the number line up... What do you know. Using and ground tooling is fine and i did it for two decades but sneaking up on the pitch diameter was always fun, I guess I could have ground two tools to use for the more common threads 1/2-28 and 5/8-24 but I never did. as of about three years ago I bought a Valenite threading tool with a selection of inserts. I have a box of 24 TPI inserts for the most common stuff. It sure does make life easy and produces a very nice finish.

Just an FYI I bought a toolmakers microscope with .0001" dials and 30X scope. So any of this stuff that is hard to measure. well if i can get it on the microscope I can measure it. I may have to do a boat load of reverse math to get the dimensions I need but I can trust my numbers. I need to get a DRO for that thing to make it easier to do that math. but that's another issue.

Kerry,

Do you have an FFL to receive firearms, or is it walk-in only?

George

Walk in's only. My city will not allow a shop like mine to exist in a home. One more reason I need to buy a house in the county jurisdiction

thanks. Next time I'm in San Diego, I'll get in touch with you.

George