Measuring internal Threads

Pieper Barrel Plug Casting.JPG


Good thing I ran the casting or I would have assumed it was 18 TPI and made up a test plug only to have it jam. That would be my usual approach. Here is the Cerro Safe Casting I made.
 
Allan said:
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.
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Here's something I posted using epoxy putty to make an internal thread plug. Did basically what you suggested, lubed the inside with LPS 1 lubricant, mixed up the epoxy putty, mashed it in and unscrewed it. Easy peasy, no issues at all.

Bruce

https://www.hobby-machinist.com/thr...did-you-make-in-your-shop-today.67833/page-51
 
Thanks, BG.
How dimensionally stable is the epoxy you used? Does it shrink or expand much?
 
Was going to say that one thing I like about Cerro Safe is that if it sticks you can just heat it up and melt it out and try again. I also did a chamber cast on an old Ross rifle yesterday. Never done one before and the thing would not come out although the instructions say to push it out with a cleaning rod. Much heavy pounding would not dislodge it so I melted it out. Apparently it has throat erosion from the old cordite powder and the erosion ring was deep enough to lock it in place. Had it been epoxy it would have been real challenge to get it out again given how inaccessible it was.
 
Allan said:
Thanks, BG.
How dimensionally stable is the epoxy you used? Does it shrink or expand much?
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According to the data sheet shrinkage is <1%. That'd be less than 0.007" in my case.

Bruce
 
Not bad but a bit much for my critical dimensions. But maybe not. I still have to start a test plug on the large side and work down to a fit anyway.
Cerro Safe shrinks slightly at first but within an hour expands. It will eventually stabilize at + .0025" on something like cartridge case.
 
Good thing I ran the casting I would have assumed it was 18 TPI and made up a test plug only to have it jam. That would be my usual approach.
 
So how would you cut a thread of 19 tpi?
 
Actually my lathe has a setting for 19 TPI. I was a little dubious so I checked it out. I guess that 19 TPI 55 degree thread is still used all over the world so these older lather must have been set up with that in mind. Kool.
 
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