gappmast
Cast Iron
- Joined
- May 13, 2007
- Location
- California
I'm installing a barrel on a Remington rolling block with 12 TPI square threads. Are these truly square threads or is there a small angle on the sides. Any impute would be appreciated.
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I have cut one square thread for an M1870 Trapdoor Springfield and picked up an M1903 and a Garand thread while rebarreling them. The tools I ground from HSS blanks. Not much different from other grooving or thread tools but they are a true 90° thread form and you do have to hold the dimensions. Give your lead screw and half nuts a very good cleaning before you start. A nominal 60 production thread can wander a tiny bit to and fro on the thread dial, but the square threads have to track pretty much dead nuts. Hey it's what we do. Take your time, feed straight in with the compound, and good luck with them. A blade micrometer is best to check your progress proceeding with light cuts.
I have cut one square thread for an M1870 Trapdoor Springfield and picked up an M1903 and a Garand thread while rebarreling them. The tools I ground from HSS blanks. Not much different from other grooving or thread tools but they are a true 90° thread form and you do have to hold the dimensions. Give your lead screw and half nuts a very good cleaning before you start. A nominal 60 production thread can wander a tiny bit to and fro on the thread dial, but the square threads have to track pretty much dead nuts. Hey it's what we do. Take your time, feed straight in with the compound, and good luck with them. A blade micrometer is best to check your progress proceeding with light cuts.
A square thread will work on an M1, and many have done it, but it is actually a 10 tpi stub ACME thread. Same with M14. 14-1/2 degrees per side.
OK actually measured my rolling block barrel tenon
0.9675 major dia
0.924 minor dia
1.461 overall tenon length
0.581 turned down to minor dia.
now there are some details that have to be cut
best to get a barrel stub from Ken Womack.
see attached photo
View attachment 288916
How did this turn out? I have a line on a #1 rolling block in .43 Egyptian in really poor shape that I am thinking of converting to a .50 caliber inline muzzle loader. Was it hard to remove the barrel? Is there enough meat in the receiver to cut out the square threads and replace them with V threads?
Oh, BTW, you can't generate a 'perfect' square thread internally even by milling with the cutter inclined to the lead angle. It's always going to have angled (actually curved) sides to it. But as Kendog notes regarding an M-1 (I didn't know they were ACME, probably aught to look close at the extra Kreiger in my shop cabinet), close enough ...
An ACME thread might be millable with an inclined cutter. I'm not sure. They can not be done by conventional thread milling. Only a single point cutter or a tap will generate the proper form.
That was in context with milling the threads. Sorry. Single pointing, or tapping will do it. Milling, with a round cutter obviously, results in the leading and trailing teeth going out of bounds of the helix of the thread. Similar to how running a piece of wood across a table saw at a slight angle to the plane of the blade results in a cove cut instead of a wider straight sided groove.
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