Gunsmithing the intricacies of threading?

[Heretoimproveforhunting]

looking for some input from some of the smiths on here in regards to whether the solution to the following is just 'cleaning up' the existing threads, or would it have to be cut and rethread.

background:

i've now received two barrels from a manufacturer threaded 5/8-24. in both cases when attempting to install brakes from another manufacturer, ive run into instances of incompatibility. in the first event the brake got stuck. had to be cut back, etc.

On the 'replacement' barrel, once i started getting resistance again i stopped and called manufacturers of both parts. both have taken it in and said their respective product checks out to their specs. Barrel manuf showed me 5-6 pictures of various competitor brakes / threadcaps threaded fully on the barrel. brake manufacturers QC group identified no issue with their product, but gave me the following regarding their thoughts on the barrel threading:

" We measured the barrels thread pitch and we found that the pitch was oversized at .602, five thousandths over the acceptable range. We utilize class 2 threads for our adapters where the acceptable range is .59270 through .59670."

based upon my limited understanding of pitch (peak to peak - correct me if im wrong), is this something that can be fixed by re-chasing the threads a bit?

i tried to understand the classes. it just seems odd to me that other manufacturers stuff went on and not this one. does that mean everyone typicaly uses class 1 for threads for MDs?

 

[Mordamer]

One of them is telling you the truth and the other one isn't. I'd tend to believe the brake manufacturer as they actually took measurements. Muzzle threads should be cut to a 5/8-24 3A (class 3) spec and muzzle devices can be cut to a 5/8-24 2B or 3B spec (class 2 or class 3) and be compatible.

The measurement of .602" is a pitch diameter and cannot be measured on the peak of the threads. Assuming that is an accurate measurement, that pretty much tells the story. It is indeed too large to meet class 3 spec. The gunsmith that did the barrel threads is most likely the culprit. He is doing something wrong when it comes to cutting his threads to a standard.

 

[The King]

He probably cut the thread boss oversized and then threaded until he had peaks.

It’s a common issue with how folks are taught threading - you oversized the boss a little to ensure you get sharp peaks all the way around - but then you check it as you cut past the peak.

Some smiths forget they did it that way and just peak them.

One of them is telling you the truth and the other one isn't. I'd tend to believe the brake manufacturer as they actually took measurements. Muzzle threads should be cut to a 5/8-24 3A (class 3) spec and muzzle devices can be cut to a 5/8-24 2B or 3B spec (class 2 or class 3) and be compatible.

The measurement of .602" is a pitch diameter and cannot be measured on the peak of the threads. Assuming that is an accurate measurement, that pretty much tells the story. It is indeed too large to meet class 3 spec. The gunsmith that did the barrel threads is most likely the culprit. He is doing something wrong when it comes to cutting his threads to a standard.

 

[The King]

I don’t think much thought went into it frankly. Mostly because before suppressors it didn’t matter too much - and these days we just reuse the old paradigms.


For example, the cone shaped barrel shoulder is superior in every way for mounting a suppressor. And in some ways probably superior for mounting a barrel to an action, too.

Using a forcing cone would, for example, make the Bar-loc work right.

A kindred spirit (you had me when you mentioned fit class)

Let me give you the engineering data in English (but if you need it can go full technobabble)

I don’t know if the people who make these things even know class fitting exists, actually engineer the threads based on the load or they just grab the closest thread that fits the round stock. I see no indication that any significant thought went into any of it. I have never seen a published standard that the industry would adhere to on this issue or even stresses the joint is designed to withstand.

Here is the short text

Starting at zero (defined as fitting a 1” pin in a 1” hole)

You can’t do it because that’s the beginning of an interference fit because there is no gap. Same with a thread. There has to be a geometric gap so they don’t rub, and air/fluid can escape.

But that gap cannot be enough to cause off center axis loading because that can cause clamping force issues or induce stressors leading to failure.

This value is a GEOMETRIC RELATIONSHIP in several planes- not a raw linear dimensional number.

Looser fits are for frequent assembly/disassembly and will tolerate some dirt- as a trade off there will be the potential for “off axis” movement in all degrees of freedom and possibly some effect on tensioning requirements.

Tighter fit classes require strict lubrication and sometimes heating and cooling just to install and are often “single use” fasteners. (father of the old wives’ tale that you should always replace nuts and bolts- for high fit classes you better)

Also, the female thread (B) is almost always true to dimension, and the male thread (A) sets or assigns the fit class.

The “pitch diameter” talking about fastener threads and not gears (measured P2P for size but at any 2 like points along the helix for overall fit when in contact) determines the surface area of contact for tensioning strength.

(this is why when you select a tap make sure the fit class is the same for the female thread and why you have adjustable dies to adjust this- don’t just randomly grab 2 and believe because both are ¼-20 they are mated)

Another consideration is the thread- if the thread is forged or rolled then the threads are super dense relative to the core-ANY DRESSING of those threads removes that super strong dense material and reduces clamp strength and joint integrity by ORDERS OF MAGNITITUDE.

So you CAN chase the threads (lathe, tap/die or file) within reason and the parts will fit mechanically and probably pull tension satisfactorily but by removing metal you run the risk of affecting indexing ( timing as some call it), tension, axial and radial alignment.

Actual results will depend on the specific joint and the modification so there is no real prognostication other than you know what you are doing – just be cautious like any machinist and if need be cut a dimensioned model and experiment.

Hope that helped- this is a complex subject and I know this is the evaporated milk version.

 

[Heretoimproveforhunting]

It is indeed too large to meet class 3 spec.

mordamer - do you know the limits of class 3A spec off-hand?

 

[Heretoimproveforhunting]

my first inference prior to the feeback here was that a class 1 would have the widest tolerances, with 2 being tighter and 3 being the tightest. (maybe tight isnt the appropriate word). but from a few remarks here do i have that backwards? type 3 would have more 'play'?

 

[Driftr76]

I believe the tolerances for an external 3a 5/8-24 are:
O.D. = .625-.6178
P.D. = .5979-.5949

 

[Heretoimproveforhunting]

picture may help me follow. BofI - on those tolerances, how do they apply in relation to my photo. A, B,C ?

with respect to the measurement the MD manufacturer gave me (this is a QD brake associated with a suppressor) what is that referring to - A, B, C ?

would welcome direction to any particularly good diagram on the web. my quick searches werent very enlightening

 

[Driftr76]

 

[Mordamer]

picture may help me follow. BofI - on those tolerances, how do they apply in relation to my photo. A, B,C ?

with respect to the measurement the MD manufacturer gave me (this is a QD brake associated with a suppressor) what is that referring to - A, B, C ?

would welcome direction to any particularly good diagram on the web. my quick searches werent very enlightening

Play with this calculator.

UN imperial screw thread calculator

theoreticalmachinist.com

 

[Driftr76]

To measure pitch diameter, you're either gonna need a thread mic or thread wires and an o.d. mic.

 

[Heretoimproveforhunting]

i'll play with the calculator. drifter thanks for the photo. so if i understand correct, the PD could be reduced. but a PD can't be increased because the metal is already gone.

 

[CHADPEZZLE]

i'll play with the calculator. drifter thanks for the photo. so if i understand correct, the PD could be reduced. but a PD can't be increased because the metal is already gone.

Correct. Pitch Diameter can be reduced, not increased.

If the barrel threads are out of tolerance as the Muzzle Brake manu. says, it could possible be re-threaded/chase the threads. There isn't a large margin for error and the setup is critical to get things concentric to the bore.

Taking of .005" total doesn't leave a lot room to work with.

Unless the barrel manufacturer says the PD is different than what the other guys measured, I'd be inclined to assume it's the problem, and even though other brakes thread on it's not cut to a standard/tolerance that most would agree is acceptable.

.005" over sized on the PD is way out of tolerance when it comes to the numbers a lot machinist/gunsmiths maintain on a daily basis.

 

[J McGriddle]

Play with this calculator.

UN imperial screw thread calculator

theoreticalmachinist.com

This calculator is awesome. I use it all the time for custom/oddball threads at work.

 

[Wannashootit]

Good (and recent) video explaining thread fit/pd



Nose radius of the insert (or ground hss) is also important. Full-profile inserts will keep depth of thread to a minimum because the nose radius is specific to the thread pitch. When barrel wall thickness is minimal on sporter contours this can be an important consideration.

 

[carlsbad]

Some good information in this thread on how to manage thread class and fit. However, as the OP pointed out. many brakes etc are made in small lots in various shops and often do not meet the thread class that they are advertised as. I always ask to have the brake or muzzle device in hand if possible. Some brands I have more confidence in and can thread a muzzle to match them without the device in hand.

However, here is some guidance: Thread fit is almost always better loose than tight. For muzzle devices, the loads are not high and perfect thread fit isn't necessary. a loose fit will avoid problems and a tight fit will often cause problems. For a muzzle device that I don't have in hand I generally make the pitch diameter about .002" below minimum spec for the class.

Nobody is more frustrated than a customer with a new barrel eager to go shoot it and the muzzle brake threads on half way and gets stuck.

--Jerry

 

[Heretoimproveforhunting]

Thanks everyone. all very helpful and enlightening.

 

[Heretoimproveforhunting]

spent some time at lunch playing with the calculator link provided, and set out the 3 classes side by side. running comparisons i see how the tolerance between A and B threads clearly 'tighten' as you move from class 1 to 3. snapshot of spreadsheet attached.

back to my issue at hand. so my brake manufacturer quoted the barrel thread pitch diameter at .602. From the tables that is out of spec for A threads in all classes.

Now, one of the different adapters that the barrel manuf sent me a photo of clearly threaded on my barrel is a made by a company that specs class 3A threads for their stuff. A pitch dismeter of .602 is also outside of their spec, but whatever class B thread spec they are using is compatible (based upon pictures provided). looking at charts it would imply they use class 2b or 1b, but as these manufacturers deal in suppressors, i would think they'd stay toward the tighter end of the spectrum, ruling out 1b. But then at the specs for 2b, it would only leave about 1 thousandth between my barrel pitch diameter and a class 2b max pitch diameter. Seems pretty darn tight.

im just perplexed how these other adapters fit right on in the photos.

 

[Mordamer]

spent some time at lunch playing with the calculator link provided, and set out the 3 classes side by side. running comparisons i see how the tolerance between A and B threads clearly 'tighten' as you move from class 1 to 3. snapshot of spreadsheet attached.

back to my issue at hand. so my brake manufacturer quoted the barrel thread pitch diameter at .602. From the tables that is out of spec for A threads in all classes.

Now, one of the different adapters that the barrel manuf sent me a photo of clearly threaded on my barrel is a made by a company that specs class 3A threads for their stuff. A pitch dismeter of .602 is also outside of their spec, but whatever class B thread spec they are using is compatible (based upon pictures provided). looking at charts it would imply they use class 2b or 1b, but as these manufacturers deal in suppressors, i would think they'd stay toward the tighter end of the spectrum, ruling out 1b. But then at the specs for 2b, it would only leave about 1 thousandth between my barrel pitch diameter and a class 2b max pitch diameter. Seems pretty darn tight.

im just perplexed how these other adapters fit right on in the photos.

Class of thread doesn't equate to better suppressor alignment. The shoulder on the barrel aligns the suppressor square with the bore. We all like a nice tight thread fit, but it can cause problems like the one you are experiencing.

 

[Heretoimproveforhunting]

mordamer -

i've always leaned toward the use of adapter ayatems for all of my supressors. i understand the attraction of direct thread from the perspective of saving on adapter costs, but i have always been concerned about cross threading / galling / crappy thread job effects on a direct thread suppressor. its easy-er to have to throw out a $100 mount versus deal with a $1k paperweight. im surprised i dont hear more horror stories about people with direct thread suppressors. or maybe they are out there and i m just not looking for them

 

[LRI]

Figure your time and aggravation. Wanna mitigate that moving forward and make any/all "gunsmits" cringe when they try to feed you a line of shit with regards to threading a muzzle?

Your Jedi Weapon Lies here...


It's exactly why I "cowgirled up" and bought all this shit.

 

[Heretoimproveforhunting]

Chad -

It's very convenient that you showed up. you guys 'fixed' the first barrel i had problems with. I'll likely be sending you this one, to try to clean up the threads, but going to talk to the barrel oem one more time next week. I'd rather they do it at their cost and risk of threads being wacked. Still waiting to have barrel and adapters in hand from the brake manuf.

 

[carlsbad]

Chad,
Your gauges won't help me if your threads are perfect and the muzzle brake in .002" under. --Jerry

 

[majohnson2]

Most manufacturers use Class 2 threads to insure parts are interchangeable no matter where they go. If you can find a 5/8 24UNF die you can chase the barrel threads fast and easy. Just use lots of oil.

 

[LRI]

Chad,
Your gauges won't help me if your threads are perfect and the muzzle brake in .002" under. --Jerry

I would politely disagree and state that it does. You get two cooks in a kitchen who get told that the meal sucks and they'll both start lobbing mortars at each other.

With a set of ring and plug gauges, you know exactly who to have the conversation with. Only one guy needs to be standing with no chair when the music stops.

 

[carlsbad]

Chad,
I'm not sure you were that polite. I have NIST traceable thread gauges older than many of the members here, I'm sure older than your new CNC machinery since CNC wasn't widely used when they were made. I have a drawer full of custom thread gauges that I've made myself for threads I needed to make. I am a full believer in thread gauges. but they won't help if you're mating up to a bastard thread.

I think you understand my point.

--Jerry

 

[Dolomite_Supafly]

You might be able to use a tri needle file to clean up the threads enough to make it useable. .005” isn’t a lot and shouldn’t take too long on a lathe.

 

[Rubicon Precision]

Chad,
I'm not sure you were that polite. I have NIST traceable thread gauges older than many of the members here, I'm sure older than your new CNC machinery since CNC wasn't widely used when they were made. I have a drawer full of custom thread gauges that I've made myself for threads I needed to make. I am a full believer in thread gauges. but they won't help if you're mating up to a bastard thread.

I think you understand my point.

--Jerry

You shouldn’t be making bastard threads, unless you are engineering/designing something from scratch for a particular reason. If the boy threads on the barrel are in spec, and the muzzle device won’t fit, the muzzle device is out of spec and needs to be repaired/replaced. Specs are there just for this very reason.

 

[carlsbad]

Rube,
So if your customer sends you a muzzle brake that isn't per spec do you return it and tell them you can't fit it?

--Jerry

 

[Rubicon Precision]

Rube,
So if your customer sends you a muzzle brake that isn't per spec do you return it and tell them you can't fit it?

--Jerry

If the customer supplied brake is out of spec, I absolutely would recommend they send it back for repair/replacement. Why would you make your work out of spec to mate to a single out of spec muzzle device? It only makes sense for the part that is OOS be repaired.

Edit: you purchased a bolt from one manufacturer and a nut from another. They do not screw together. Turns out the bolt is in spec but the pitch diameter of the nut is too small, why would you alter the bolt?

 

[carlsbad]

Ok. I'm doing it wrong. I try to make it easy on my customers and don't make them argue with a manufacturer so I won't have to take another pass off the muzzle threads.

I don't want to argue. You keep doing it your way and I'll keep doing it mine.

--Jerry

 

[alwaywatchyoursix]

I only understand half of what I'm reading, but I'm following this closely now because I'm having a very similar problem. I've got a barrel I recently acquired from another SH member, and the muzzle threads are messed up. Some items, like a really loose thread protector, will go on with just a little bit of resistance, while others will only make it to just before the damaged threads. And for some reason (probably lack of knowledge) I can't use a die to clean up the threads.

Just trying to make sure I know what I'm doing before I end up screwing things up and having to get it re-cut and re-threaded.

 

[TACC]

I definitely learned alot about threading here today. I guess I am just fortunate to not have this problem as of yet, but at least I will be a little bit better prepared if it does occur.

 

[carlsbad]

I only understand half of what I'm reading, but I'm following this closely now because I'm having a very similar problem. I've got a barrel I recently acquired from another SH member, and the muzzle threads are messed up. Some items, like a really loose thread protector, will go on with just a little bit of resistance, while others will only make it to just before the damaged threads. And for some reason (probably lack of knowledge) I can't use a die to clean up the threads.

Just trying to make sure I know what I'm doing before I end up screwing things up and having to get it re-cut and re-threaded.

If it is a used barrel, the threads could just be dirty. Clean with fine wire brush.

If you are using a used muzzle brake, then often the Muzzle brake threads have carbon buildup on them.

Make sure your muzzle brake is the same pitch as the threads on the barrel. While threads are somewhat standardized, it is not uncommon to have different threads, e.g., 5/8-24, 5/8-28, 5/8-32.

In my experience it is very unlikely that the threads on the barrel are oversize but it is fairly common for muzzle brakes to be undersized. .

 

[alwaywatchyoursix]

If it is a used barrel, the threads could just be dirty. Clean with fine wire brush.

If you are using a used muzzle brake, then often the Muzzle brake threads have carbon buildup on them.

Make sure your muzzle brake is the same pitch as the threads on the barrel. While threads are somewhat standardized, it is not uncommon to have different threads, e.g., 5/8-24, 5/8-28, 5/8-32.

In my experience it is very unlikely that the threads on the barrel are oversize but it is fairly common for muzzle brakes to be undersized. .

Yep, first thing I did was scrub and degrease the threads using a fine wire brush. They are definitely damaged. You can see what look like flattened and widened spots on the peaks of the external thread.

The muzzle brakes I'm using, at least one of them has never been used on any other barrel. I've got a thread protector that will go on without any major issue, but you can tell when it's hitting the more severely damaged threads because there's a little more resistance and it makes that metal-on-metal squeaking sound.

Using an Area 419 Hellfire adapter, the resistance goes up quite a bit when it hits the most damaged areas. I could probably get it on with a wrench, but I'm worried about it never coming off. If I'm understanding what I've seen elsewhere on here, galling could become an issue? I'm not sure if anti-seize would be enough to negate this.

The Surefire muzzle brake I have becomes so tight as soon as it hits the first damaged area that I'm not sure even a normal wrench would be enough. It's definitely new as it was just an extra I had sitting around, but to be fair, I do wonder if maybe it's somehow undersized. When I pull it off, I can see that the barrel threads have actually scraped away some of the metal in the brake and left the shiny metal underneath exposed.

Those are the easiest and the hardest of the ones I've tried. I have a few others that fall in between, but at the end of the day, the threads are visibly damaged and I'm not comfortable trying to He-Man something on just because of impatience.

I've used some thread files with the correct pitch to try and clean them up. Hasn't seemed to make a difference. And when I put the barrel in the vise and try to use a die to chase the threads, I end up with so much resistance just trying to get it started that I'm worried I'll cut all new threads.

I'm more amateur mechanic than machinist, so I have used dies before, but not frequently, and I'm being a little more conservative in my approach here because a barrel isn't as easily replaceable as a simple bolt.

 

[ScottDWallace]

Easily the best thing to get you started down the path of good threading. By determining the PD and taking the Major Dia, you can easily call out the offending party.

Brown & Sharpe 599-4816 48-Piece Thread Measuring Wire Set: Amazon.com: Gateway

Brown & Sharpe 599-4816 48-Piece Thread Measuring Wire Set: Amazon.com: Gateway

www.amazon.com

Also, find a copy of Machinery's Handbook. Super handy for literally everything we can and could do in a shop. You can reference the various thread tolerances there.

Machinery's Handbook, Toolbox Edition: Oberg, Erik: 9780831130916: Amazon.com: Gateway

Machinery's Handbook, Toolbox Edition [Oberg, Erik] on Amazon.com. *FREE* shipping on qualifying offers. Machinery's Handbook, Toolbox Edition

www.amazon.com

 

[alwaywatchyoursix]

what you are describing is starting to sound like you could have some threads simply cut wrong. ( this is without seeing it obviously)

- Did anything ever screw on to this barrel in the first place?
- I might suggest you putting dychem on the thread and screwing 2 different devices with the same thread and see if they are binding the same.
If they are that's a good indicator you may have an improper thread

- Have you used a thread gauge to verify the male thread yet?

I can get a thread protector on with just light effort, and it'll go until it bottoms out. The Surefire brake, which is the toughest to get on, spins on just fine until it runs into the damage portions of the threads. Once it hits the damaged portion, it becomes VERY stubborn and the barrel threads are actually cutting into the nitrided metal of the brake.

I haven't used a thread gauge yet. More mechanic than machinist, so the only thread gauge I have on hand is the kind that just tells you the size of the bolt and the TPI. Not too bad considering I paid about $5 for them at Harbor Freight over a decade ago. But I might pick up a set like @ScottDWallace linked above. Or some ring and plug gages like LRI linked higher up. I'm not sure how often I'll use them, but I have a problem when it comes to hoarding tools anyways.

Just so it's clear, the threads are most definitely damaged. Like, visibly so in some areas.

I ordered a split rethreading die a few days ago, so we'll see if that fares any better once it arrives. Worst case scenario is finding out that the threads are not salvageable and the barrel needs to be cut and rethreaded, in which case I'll be forced to finally track down a decent machinist in my area.

Thanks for the dychem suggestion also. Hadn't thought of that.

 

[ScottDWallace]

The one he is describing is the high tech model and requires some precision use.

I guess I wasn't exactly clear as how to use these, my apologies. They are quite the opposite from high-tech, but benefit greatly if you have a third hand! You place two wires (all of the same diameter and size determined by the instructions with the wires) on one side of the threads, and with your third hand, place the single wire on the opposite side. Use a micrometer to measure the across the wires. You will take that measurement, do a little math in accordance with the instructions, or your new machinery's handbook, and you will get your pitch diameter, or PD. Look up the PD tolerance for the type of thread you have and you will instantly know where your problem lies.

I will say that this is usually for machinist's, gunsmith's, and operators to verify threads, but it is indispensable for anybody that works with threads in general. You can then use the PD measurement to adjust your split ring die or filing.

So if I understand your situation right, you have a comp that will not thread on completely. There are really only three things that could be in error that comes to mind. Though, I've only had one cup of coffee, so forgive me if I've missed one or two. Crest height (major diameter) is too high, which can sometimes be addressed with a quick and LIGHT filing. Pitch Diameter is out of tolerance on the high side. Or what @Blacksmith of Isaiah said, and which is the most likely suspect, the thread pitch is just wrong. The barrel maker/gunsmith could be threading on a metric lathe and uses a setting that is "close enough". If you don't have a TPI gage, you can set your calipers to 1.000" and just count the threads. That's assuming you have 1" of thread. Do math accordingly if you have less.

Good luck and keep us posted!

 

[alwaywatchyoursix]

The one he is describing is the high tech model and requires some precision use.

I was suggesting this one- highly accurate, quick, dirty and will tell you where to file and how much ( and will tell you exactly what thread you have and if its at a standard 60 degree angle or even metric on one and std on the other)

That's similar to how the ones I have work, though considering the low quality of them, I've only ever used them to count TPI. The teeth on mine aren't cut nearly deep enough to be able to verify anything more than TPI.

I guess I wasn't exactly clear as how to use these, my apologies. They are quite the opposite from high-tech, but benefit greatly if you have a third hand! You place two wires (all of the same diameter and size determined by the instructions with the wires) on one side of the threads, and with your third hand, place the single wire on the opposite side. Use a micrometer to measure the across the wires. You will take that measurement, do a little math in accordance with the instructions, or your new machinery's handbook, and you will get your pitch diameter, or PD. Look up the PD tolerance for the type of thread you have and you will instantly know where your problem lies.

I will say that this is usually for machinist's, gunsmith's, and operators to verify threads, but it is indispensable for anybody that works with threads in general. You can then use the PD measurement to adjust your split ring die or filing.

So if I understand your situation right, you have a comp that will not thread on completely. There are really only three things that could be in error that comes to mind. Though, I've only had one cup of coffee, so forgive me if I've missed one or two. Crest height (major diameter) is too high, which can sometimes be addressed with a quick and LIGHT filing. Pitch Diameter is out of tolerance on the high side. Or what @Blacksmith of Isaiah said, and which is the most likely suspect, the thread pitch is just wrong. The barrel maker/gunsmith could be threading on a metric lathe and uses a setting that is "close enough". If you don't have a TPI gage, you can set your calipers to 1.000" and just count the threads. That's assuming you have 1" of thread. Do math accordingly if you have less.

Good luck and keep us posted!

My bad if I made it sound like you were confusing me. I get what you're saying on verifying the thread measurements so I can find out exactly which part is at fault.

The thing is, everything (except the 5/8"-24 die I tried) does spin on UNTIL it hits the damaged threads. Where the various muzzle devices differ is in how they behave once they get to that point. I'm sure that's mostly a matter of exactly how to spec each part is cut. But before I start worrying about how to spec each device is, I'm planning on repairing the damaged threads.

If I'm still having fitment issues once I've repaired the threads, then it's definitely time to put your recommended tools to use and see how off the barrel and device threads are.

I do appreciate all the suggestions everyone here has made, so don't take my decision not to use them immediately as a sign of being butthurt or something.

 

[kthomas]

If the customer supplied brake is out of spec, I absolutely would recommend they send it back for repair/replacement. Why would you make your work out of spec to mate to a single out of spec muzzle device? It only makes sense for the part that is OOS be repaired.

Edit: you purchased a bolt from one manufacturer and a nut from another. They do not screw together. Turns out the bolt is in spec but the pitch diameter of the nut is too small, why would you alter the bolt?

This is exactly what should be done.

By doing otherwise just creates further potential frustration for the customer if he wants to try a new self timing brake or wants to install a direct thread suppressor.

I would fully expect my gunsmith to send back and replace an out of spec part, rather than bastardizing the barrel threads.

 

[Shootinleftyflip]

I guess I wasn't exactly clear as how to use these, my apologies. They are quite the opposite from high-tech, but benefit greatly if you have a third hand! You place two wires (all of the same diameter and size determined by the instructions with the wires) on one side of the threads, and with your third hand, place the single wire on the opposite side. Use a micrometer to measure the across the wires. You will take that measurement, do a little math in accordance with the instructions, or your new machinery's handbook, and you will get your pitch diameter, or PD. Look up the PD tolerance for the type of thread you have and you will instantly know where your problem lies.

I will say that this is usually for machinist's, gunsmith's, and operators to verify threads, but it is indispensable for anybody that works with threads in general. You can then use the PD measurement to adjust your split ring die or filing.

So if I understand your situation right, you have a comp that will not thread on completely. There are really only three things that could be in error that comes to mind. Though, I've only had one cup of coffee, so forgive me if I've missed one or two. Crest height (major diameter) is too high, which can sometimes be addressed with a quick and LIGHT filing. Pitch Diameter is out of tolerance on the high side. Or what @Blacksmith of Isaiah said, and which is the most likely suspect, the thread pitch is just wrong. The barrel maker/gunsmith could be threading on a metric lathe and uses a setting that is "close enough". If you don't have a TPI gage, you can set your calipers to 1.000" and just count the threads. That's assuming you have 1" of thread. Do math accordingly if you have less.

Good luck and keep us posted!

A good life hack for using thread wires is a small smackeral of grease to help the wires stick to the threads whilst you get your mic around the wires, however it’s not mandatory. While a third hand would be cool rest assured two hands can do it easily enough just takes practice. If for some reason you don’t have any grease always put two wires on the bottom of the thread and carefully and gently hold the wires with the bottom face of your mic and slide the top wire between the thread and top face of the mic. A cloth under your work is always a must. Because those little buggers are not fun to try and find in a lathe or on the shop floor. But the more you use/practice with them the less you’ll drop them!

Have a great day!
Calli

 

[Driftr76]

A good life hack for using thread wires is a small smackeral of grease to help the wires stick to the threads whilst you get your mic around the wires, however it’s not mandatory. While a third hand would be cool rest assured two hands can do it easily enough just takes practice. If for some reason you don’t have any grease always put two wires on the bottom of the thread and carefully and gently hold the wires with the bottom face of your mic and slide the top wire between the thread and top face of the mic. A cloth under your work is always a must. Because those little buggers are not fun to try and find in a lathe or on the shop floor. But the more you use/practice with them the less you’ll drop them!

Have a great day!
Calli

Yeah. I have more than one set of thread wires with a few missing here and there.

 

[Terry Cross]

A good life hack for using thread wires is a small smackeral of grease to help the wires stick to the threads .....

Skip the grease. It is just a lure to get any other micro debris into the measuring loop. Keep your wires and your thread forms clean when measuring.

If you are using wires to check your threads and are not doing this, you should try it. An old machinist dude showed me this over 30yrs ago. Put the tape on and just keep it there until you wear it out....

Once you learn a method of holding, you will be quick, clean and repeatable. WAY, WAY easier to retain the wires when handling and if you do succeed in dropping one it is easy to locate and recover.

I have a few thousand dollars in ring and plug gauges. They are used for checking off most work before it comes out of the machine but I still use the same sets of wire (about 4 sets) quite often.

Hope this helps ya'll as much as it seemed to help me.


./

 

[RonA]

Use a large pencil eraser to hold the wires. Just poke the ends of the wires in the approximate location and then you can squeeze them down onto the thread with the fingers of one hand and measure with the other. Not grease either.

 

[Wannashootit]

FLEXBAR 16707 .018

BenefitsAn accurate and inexpensive way to check threads.Makes thread triangles, thread Micrometers and all other current methods obsolete.ApplicationsAs easy as selecting the proper wire sizes, matching the wire size with the proper P.D. Check, slipping two wires into the holder, placing the...

www.travers.com

 

[carlsbad]

I used wires until i bought my first thread mic 15 years ago.

 

[ScottDWallace]

@Terry Cross this is pure genius. A small pain to store them easily, but WAYYYYY easier to find them when they get dropped in a pile of chips on the CNC lathe!

 

[DAVETOOLEY]

Thread mics aren't that expensive if you find old Starrett or Brown and Sharp fixed anvil mics. That's what I started with before scavenging sets. with anvils. I still use some that I paid $25 for.
Example

BROWN & SHARPE No.153 14 to 20 TPH SCREW THREAD MICROMETER | eBay

IT IS IN GOOD WORKING CONDITION.

www.ebay.com

14 to 20 thread pitch micrometer by Brown &Sharpe | eBay

Used Brown & Sharpe 0 to 1 in. thread micrometer, 14 to 20 tpi. In good working condition. <br>With wooden box and paper work

www.ebay.com

 

[carlsbad]

I installed a muzzle brake today, 1st time since this thread started. Above I posted that I much prefer to have the brake in hand because so many of them don't meet the thread spec they advertise. I don't want to name names of those that I've found to be out of spec. It is a small world.

Today I installed a Fat Bastard 3/4 -24. The thread spec is 2A. I had it in hand so I cut the threads to fit the brake exactly like I like them. Then I measured them. I expected it to be on the loose since since I cut my threads looser than a lot of machinists--the tendency is to cut them too tight because it seems to most that tighter threads means better fit, but too tight is just as bad as too loose. After I got it like I wanted it, i took the thread mic out of the drawer and I measured the pitch diameter at .721", at the high side of 2A threads.

--Jerry

 

[RPN]

If you are having problems with small parts, gravity and the floor, use a large, clear plastic bag for assembling (or disassembling) things in.
Anything dropped, flying off or just being a bastard gets caught in the bag.