Thread gauge

[49Reo]

I am on the hunt for a "square thread" thread pitch gauge. Anyone know where I can find one? All I can find is Whitworth, Metric, and SAE gauges. Any help would be appreciated.

Thanks in advance;
Reo

[rich.petkevis]

Maybe these guys have it:http://www.threadcheck.com/

Acme threads are often called square thread.

[marvelshooter]

Could you tell us a little more about what you are doing? Are you talking about a straight sided thread and not a 29 degree acme? If you mean the acme gauges are available and if you mean a true 90 degree square thread you don't need one.

[Ole Joe Clarke]

Acme threads are not the same as square threads. Acme threads have a 29° angle on the sides. A Machinery's Handbook, especially an older edition, has tons of information on threads.

[screamingjohnny]

I would consult a Machinery's hand book as it should have the measurements for the thread size you need.

[49Reo]

Re-barreling a Remington roller, Danish model..

[Cap'n Morgan]

Re-barreling a Remington roller, Danish model..

I don't know about the Remington, but 12 TPI thread was a common standard in Scandinavia.

Unscrew the barrel a number of turns, measure the gap between action and barrel and divide it with the number of turns. You now have the thread pitch for one turn. The number will probably be very close to 0.0833 = 12 TPI

[Ballistics in Scotland]

Acme threads are not the same as square threads. Acme threads have a 29° angle on the sides. A Machinery's Handbook, especially an older edition, has tons of information on threads.

Very true, and mixing up one with the other is a lot more dangerous than 60 and 55 degree, as many American gunsmiths do with Mausers.

It is rare or unknown for Acme threads to be used for barrel attachment, but fairly fine pitched ones would be good for anyone designing from scratch. The great virtue of Acme or square threads compared with V-threads is that for a given amount of turning force more goes into lengthwise force and less is lost in friction.

You can measure the pitch of a square thread with a caliper or steel ruler. A V-thread gauge will do it too, if you hold it properly in line with the thread, and make sure the gauge contacts one side of the square grooves. Best of all if you have the original barrel and it isn't a wobbly fit when loosened, is to turn your gun into a micrometer. Keep the barrel in the action and use feeler gauges or scraps of precision ground steel to determine how much of a gap one or two turns make.

[reed1911]

IIRC are ACME threads not intended to hold torque? As I recall (long time ago) I was instructed that for holding torque v-threads are much superior, while ACME/Butress/Square are intended for strength in the lateral motion. Please correct me if I am wrong.

[Cap'n Morgan]

The larger the included angle, the larger the friction in the thread, but most holding torque/friction is created between the part and the bolt head or nut.

ACME or trapeze threads are mostly used for moving stuff, like in lead-screws, where you want a large lead/turn to diameter ratio - sometimes with multiple starts. For some bizarre reason ACME threads has an included angle of 29° while ISO threads are 30°. They are not designed to bear on the flats, but only on the flanks and as such can take a large load in both directions.

[49Reo]

I have yet to pull the barrel, but is supposed to be(so I've been told and read, is 12 tpi, square. But, I watched a video the other night,(and can't find it now, to post here) and the guy was cutting 12tpi, 29* included angle, for a Danish Roller. Once I find my barrel vise(I've recently moved and can't find half my stuff) and make an action wrench, I'll pull the barrel, then measure to be sure. Was just trying to get everything I might need lined up before hand. Thanks for all the good intel, folks; if I find that video of the guy cutting 12 TPI 29* included angle for a Danish roller I'll post it. Was a good vid, showed him making the cutter, and all.

And as I'm sure you all have figured out by now, I am not a machinist. I do have a small mill-drill and a 12x28" lathe I like playing around on; this will be my biggest and most critical, precision wise, job I have done, which is why all the questions. I have mostly made engine parts, like valves, shafts, bushings, etc, for antique one-cylinder engines. Again, thanks for all the intel.

[Ballistics in Scotland]

IIRC are ACME threads not intended to hold torque? As I recall (long time ago) I was instructed that for holding torque v-threads are much superior, while ACME/Butress/Square are intended for strength in the lateral motion. Please correct me if I am wrong.

That is all true, but in practice no thread of the kind of pitch used for barrels is at all likely to unscrew in use. You have to tighten it up firmly, but it needn't be anywhere near as tightly as you sometimes find in military rifles, which have to stand extreme temperatures and the use of the bayonet and other abuses.out

The pitch does affect the security with which the thread will lock in position. Most thread system have two series of different pitches, e.g. UNF and UNC, Whitworth and BSF, metric coarse and fine. In all cases the coarse one is about the strongest, with about an equal chance of stripping and of breaking in two. This isn't an exact science, for the relative chances are different for different metals, and overtightening is a bit different from longitudinal tension. The fine series is less likely to unscrew under vibration etc. This matters very little for barrel threads, but is extremely important for scope bases, hence the industry standard 6 - 48, which is finer pitched than UNF.

The logical extension of the coarsest thread is rifling, in which producing longitudinal motion by turning is impossible, but longitudinal motion produces rotation. But I think you

[KenH]

I have yet to pull the barrel, but is supposed to be(so I've been told and read, is 12 tpi, square.

Yep, for Danish/Swedish rollers "most" of the time it's 12 tpi square thread. I do have one Swedish roller that's a fine thread - I need to pull it down and measure what thread it is.


I watched a video the other night,(and can't find it now, to post here) and the guy was cutting 12tpi, 29* included angle, for a Danish Roller.

When you find that video I'd LOVE to have the link. I've been practicing cutting 12tpi square threads on an aluminum barrel stub in prep for installing a new E.R. Shaw 45-70 barrel I've got.

Ken H>

[John Taylor]

Most square threads have the groove width the same as the land. Use a standard thread pitch gauge to check the threads per inch. 1" and divide by the number of threads per inch ( 1 divided by 12 = .0833) divide that by two ( .0833 divided by 2) = .0417. Make a square cutter about .045" wide to cut the groove. Do not use the compound, just run the cutter in about .005" each pass with the gears set to run 12 threads per inch. On a rolling block there is a portion of the barrel that is the miner diameter, ( bore size in action) this will give you an idea of when the depth of cut is close.

[KenH]

John, that's exactly the way I cut square threads on the couple of practice barrel stubs I've made. I only use the cross slide to feed about .005" depth at a time. I have a VFD on my lathe, so I just run forward, back cross slide out .010" or so, reverse, run cross slide back in .015", go forward. Just a few times until I've got the .041" depth, which is just where the barrel is cut to the minor diameter for the extractor slot.

I'm getting better at setting headspace also - next step is to make a spider for holding barrel at opposite end of spindle to make sure the bore is centered with spindle bore with 4-jawed chuck.

Thanks to all the nice folks here for sharing info - I've sure learned a LOTS..... but still LOTS 'n LOTS more to learn.

Ken H>