[4]

Measuring internal Threads

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
I have an old Pieper Rolling block rifle action that I want to put a barrel on. I have no original barrel. I am thinking of putting an N0. 4 Lee-Enfield barrel on it. Cut it short, turn it down thread it and rechamber it for 32 S&W Long. Bullet diameters are the same. Problem is I am not sure what the OD of the threads should be. How does one go about measuring the threads on an ID of a hole less than 1" diameter? I don't think the three wire system will work.
 

jwmay

Active Member
Registered
Joined
Dec 3, 2017
Messages
446
Here’s a crazy idea. Turn a soft wood plug just a little larger than the hole you want to measure, (maybe even turn a tapered plug) and screw it into your unknown threaded hole. The softwood should yield to the steel threads. When you take it out, you should have a near identical threaded plug for that hole. Now you have something to measure. I know very little about guns by the way, so I’m making an assumption that the plug would be near enough for you to identify the thread, if this type of thing is standardized. Terrible idea?
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Worth a try. Not sure how accurate it would be. Maybe if I used maple...? I was thinking along similar lines anyway. Making a steel plug and working it down until it fits the hole nice and tight. Then measure with 3 wires and duplicate the thread on the barrel.
 

RJSakowski

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Feb 1, 2015
Messages
4,345
MSC and other suppliers sell facsimile compound designed to duplicate hard to measure surfaces but it is expensive. Your idea to make a steel plug to fit is probably your best bet.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
RJ, you have me thinking. I wonder if JB weld would work if the threads were well waxed? Don't know if it shrinks or not.
 

RJSakowski

H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Joined
Feb 1, 2015
Messages
4,345

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
RJ, Cerro Safe is a great plan and I think I ordered som ea few years ago and forgot about it. This reecisever would take a lot of metal since the barrel goes a little over 2" into it. I'll see how much I have. I bought it to check the chamber dimensions on my Ross rifle. Guess I should get on that project, too.
 

MarkM

Active Member
Registered
Joined
Apr 23, 2017
Messages
495
I don t own a rifle so looking at this just as mating threads.
The I. D. Of the threaded hole diameter isn t where you get your fit. You can stray off somewhat and make no difference. Obviously you can go too far off and make it impossible to attain a good thread but a few thou under or over what you measure will probably not matter. Common sense here. Not bigger than your major and a few under will be fine. You can easily measure the pitch of the thread with normal pitch guages.
Your pitch diameter and where the two mate from the internal and external thread is what matters and gives you your fit.
Measure your i.d. bore out your hole and start threading. Make your own guage by threading the opposite wether i.d. Or o.d. Then use that thread guage you made for your final part. Just thread until your own guage has the right fit you want than have at her or buy a set of go and no-go,thread guages for the class of thread you want.
 
Last edited:

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Thanks for the reply, MarkM.

You are right it is just about mating the threads. But I think you may have misread my question. You say, "measure your i.d. bore..." That is what I need to know how to do and what I was asking- how does a guy measure the major diameter of a hole less than 1" in diameter let alone determine the thread pitch and form?

Since this was a Belgian made turn of the previous century firearm the thread is unknown. It seems to use various threads. Again, since the bore is so small it is hard to get a read on the thread pitch and profile. One cannot see the thread pitch gauge perpendicular to the gauge. I have played around with it a bit and think I have the thread figured out but still have some niggling doubts.

The idea of a cerro safe casting would make that thread determination a lot easier. It would also make the major diameter of the threaded hole easier to measure.

In any case I would make up a plug and turn the threads a bit at a time, as you suggested, until the final fit is attained. Then I can measure with 3 wires and thread the barrel by sneaking up on it.

Gun threads are a weird mix. German built Mausewr action use a Whitworth thread. Many smithys just use a 60 degree thread and force them to fit. Seems a bit bush league to me. Many have weird thread pitches like 6-48 and some can be metric or just about any thread that was ever made. One thing that is certain is that you can't assume.
 

MarkM

Active Member
Registered
Joined
Apr 23, 2017
Messages
495
Re read again after erasing my first sentance. Sorry! Off on a Tangent I guess.
You know being out of Imperial or metric was the furthest from my thoughts. Took for granted being metric.
Could you not just use a caliper. I know it s not as precise but one good with instruments can do a decent job for the tolerance needed for threading. Just my thoughts.
How about using some type of putty or even playdough to figure your pitch and the angle of the thread. Then with your I.D. Measurement you could go to Machinery Handbook and get your proper numbers armed with enough information. Just throwing it out there!
 
Last edited:

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
I have no hole to bore I need to thread the outside of the barrel to fit the threaded hole. I don't know how I can get a caliper to read the valleys of the hole thread. I think for the sake of accuracy I'll go with cerrosafe. I already am pretty good at building in variables by accident so I don't want to engineer them in. LOL.
 

Latinrascalrg1

Brass
Registered
Joined
Dec 9, 2016
Messages
800
I would think you could make a very good copy using hot glue! Apply sometype of release compound first then you could probably place the end of a gluestick into the barrelhole and gently heat the Reciever until the glue softens and flows into the threads. Put in the fridge for a few minutes and it should unscrew right out. I would probably find a way of blocking off the back side so that the glue stays in the threaded area but if that's not possible you should be able to make it work either way.
 

rgray

Active User
H-M Supporter - Gold Member ($25)
Joined
Nov 26, 2012
Messages
1,199
12L14 is pretty inexpensive.
I'd thread as many chunks of that to what I thought it was till I ended up with a good fit.
Then thread the barrel to match your new "thread gauge".
In the few mausers I've done I've run into 4 different thread sizes. A couple of them I think were intended to be the same thread but what the operator put out that day was not on target.
 

MarkM

Active Member
Registered
Joined
Apr 23, 2017
Messages
495
Don t use the caliper to measure with but go in with a pre determined size. Set the pc. So its vertical with light coming through the bottom. Set the calipers and rock on the thread with your pre measured and set caliper. Use it like. Go no go guage then go verify with some aluminum.
Lightly oil the thread and lay putty on it. Pull it out and get your pitch and angle of thread. Have at her!
 

mikey

Active User
H-M Platinum Supporter ($50)
Joined
Dec 20, 2012
Messages
5,735
I would use an inside micrometer to find the ID. The jaws span the thread peaks and give a better reading. The problem is that you probably don't own one of these contraptions so the next best option, for me anyway, would be to take a piece of round stock and turn it down until it juuust slips into the bore and measure that. We know that production tolerances for threads can be rather coarse so we cannot rely on a standard; using a plug gauge you make would at least get you within a few tenths if you work carefully. Then you'll at least have an idea of what the minor diameter is. Then you can sort out the pitch with a pitch gauge and you'll have your thread.

It's going to be fun sorting out the thread form. I'm not a gun guy but figuring out if they used a 60 degree thread or a 55 degree Whitworth could be challenging to do by eye. Here I think the Cerrosafe stuff might come in handy.
 

jwmay

Active Member
Registered
Joined
Dec 3, 2017
Messages
446
I remember reading an article on that stuff(cerrosafe) or some equivalent. The guy was doing something with the receiver of a rifle. Wish I remembered what. Anyways, I think that’s a really good idea. I had the distinct impression from the article that the author was happy with it.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
It looks to be a 60 degree thread. And I now forget what pitch I thunk it was. I'll post a picture or two just for funzies.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
So here is the action and barrel. I need to turn the OD of the barrel down to the major diameter of the barrel hole in the receiver. The two cartridges show the approximate location of where they would sit in the chamber. So I will have to cut off the breech end at about where the breech end begins to taper into the barrel proper. If you look carefully you will see a hole drilled through the barrel in order to DEWAT it.

For now I need to determine the major diameter of the receiver threads to see if there will be enough meat on the barrel fully fit the full length of the receiver. I will need to have a face that rests against the front of the receiver to act as a depth and headspace stop.

The bullets are the same diameter as are the neck diameter on the 303 and the case diameter on the 32 S&W Long (or 32 Colt New Police, if you prefer). I hope I can get it to work.



293686
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Not sure if the 1 in 10 twist of the Enfield barrel will work. If anything it will be a tad on the fast side so I anticipate it should work OK on a slow mover like this. Kind of like windmilling a soft ball, only slower and not as flat a trajectory.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Bamban, that is a cool resource. Lots of stuff. I see that the angle of the V is not usually included. I have similar chart out of American Rifleman in the 60's but it is not as complete as this one. Thanks for sharing. Unfortunately the Pieper is not in it. It was not a very common or particularly high end rifle. Probably not worth much effort but I would like to see it live to shoot another day. I'm a sucker for old stuff and keeping them going.
 

derf

Brass
Registered
Joined
Oct 3, 2015
Messages
798
I'd use cerrosafe, but you don't have to pour the whole length. Plug up the bottom with play dough so you only have about 1/2" to pour. Coat the threads with Vaseline. While you are pouring, stick a screw driver in the middle so you have a way to unscrew it.
 

MarkM

Active Member
Registered
Joined
Apr 23, 2017
Messages
495
Earlier on when I said I was just throwing it out there. Sometimes I think just a different train of thought or like walking away for five and such so here is another I ll throw out there.
Could you not bore the hole and thread to what you can see from the outside? Or is there just not enough meat there and you d compromise the action?
Can I ask not knowing much about Gunsmithing? Is the reason there is use of such fine threads due to the fact that sometimes close enough has to work like someone stated ealier where threads were crushed together with the use of stuff maybe from another century that hobbyist would be interested to use to modify? Or am I out in left field?
 

aliva

Active User
H-M Supporter - Gold Member ($25)
Joined
Feb 28, 2012
Messages
426
Check Tom Lipton's video. He uses a material called woods metal to make a positive casting of a steering wheel spline. This might works for you. You should be able to unscrew the casting once its cooled and then take your measurements.
About 2minutes in to the video
Wood metal https://www.belmontmetals.com/product/woods-metal/
 

stupoty

Active User
Registered
Joined
Dec 2, 2012
Messages
1,203
Since this was a Belgian made turn of the previous century firearm the thread is unknown. It seems to use various threads. Again, since the bore is so small it is hard to get a read on the thread pitch and profile. One cannot see the thread pitch gauge perpendicular to the gauge. I have played around with it a bit and think I have the thread figured out but still have some niggling doubts.

If their an unknown thread on an antique I would do some research, https://en.wikipedia.org/wiki/Belgian_units_of_measurement , their it says they were metric since 1820 ish.

So it's probably metric. if you can get a thread pitch gauge in their that should be ok to figure out by feal. You could then try making test threads and screwing them in.

Stu
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Hey. Mark.
Some threads on barrels are quite fine V threads and some are quite coarse square threads. and everything in between. Check out the list that Bamban posted. I think the 1905 Ross has a double start 8 per inch square thread. What their reasons were is anybody's guess.

Stu, it seems that what was official measurements went out the window when it came to guns. As noted previously the German Mauser 98s used a British Whitworth thread. I think I'll try Cerro Safe and see for sure. A small plug of it as Derf and Aliva said with a screwdriver or something placed in it for removal seems like a pious idea. I'll check the video as well.

Thanks you all for your suggestions on such an arcane subject.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
Well I poured some Cerro Safe but it don't turn our very good. I guess the receiver was not warm enough in spite of heating it before the pour. I'll try it again tomorrow with a heat gun trained on it.

It looks like the thread is 18TPI Whitworth but its hard to tell the difference between 55 and 60 degrees on such small threads tucked inside a small hole. Maybe tomorrow's pour will work.
 

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
225
OK. Got a plug made and measured. Having it out helps immensely. I have determined that it must be a British Standard Parallel Pipe Thread
19 TPI. How weird is that?
 
[5] [7]
Top