Help threading a P14 barrel.

Casull

Casull

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I have a P14 that I want to do a project on, problem is, I have never cut square threads. Two ways to go;
1) Is anyone willing to thread this barrel for me? From there I can chamber it and so on. I am willing to pay of course.
2) Does anyone have a square threading bit with the proper angle and so on they would sell me, so I can take a try at this?
Any help would be appreciated,
Rob
 
If you have a lathe and can cut threads you can grind your own threading tool and cut practice threads on a piece of steel and then do it to your barrel..

In threading square threads measurments are most important... you don't have the ability to "feel" if you are close to being finished... the cutter and diameters and the depth of thread are are pre determined and done to those measurements... cutter is fed straight in, not at an angle...
 
I watched a master machinist, Alan Warner, thread a barrel for my Swing which is a P17 thread. He used a diamond wheel on his surface grinder to grind an insert to fit the thread and then took about 2k per cut when threading. He carefully put the insert away in case i brought it back again. It did take time but he did his usual better than perfect job. I am sure you can do the same.
 
Square thread forumals examples for grinding a tool:
Example is for 1-1/4-4 square thread

Lead=.250 in.

Single depth= .500/4
=.125in.

Double depth=2.*.125
=.250in.

Minor Diameter=1.250-.250
=1.000in.

Tan Leading angle of tool= Lead/Min.Dia.*Circ.
=.250/1.000*.31416
=.250/.31416
=.0795

The angle of the thread=4 deg,33min

The toolbit angle=4 deg,33min+1deg clearance
=5deg,33min
Tan following angle=Lead/Maj.Dia.*Circ.
=.250/1.250*3.1416
=.250/3.927
=.0636

The angle of the thread=3deg,38min.

Toolbit following angle=3deg,38min+1deg clearance
=2deg,38min.
 
Casull,
In grinding your tool for a 10TPI thread you want to end up with a cutter width of from .0505 to .051. The front relief is unimportant since clearance is provided by the work anyway. The lead angle has to be such that clearance exists. The following angle has to be less and can even be vertical since the thread will produce it's own clearance. Don't be intimidated by formulae! Just grind the damn tool so it works!
When you set up to cut the thread, you may either simply feed in on the crossfeed for each successive cut or you may set your compound at 90 degrees and feed in with the compound, returning to zero on the crossfeed. I personally set my compound at zero degrees (parallel to the axis of the machine) and feed in with the crossfeed.
As Dennis said, practice on a piece of scrap until you are comfortable with your chosen technique and confident that the tool is cutting as desired.
If you want a tight fitting square thread, you can take measurements off your receiver and use these measurements to establish your major diameter and cut depth. From there it is a simple case of "cut and try".
The important thing to remember is that square threads really cut like any other. Grinding the tool is the only difficult part and it's not that tough. Good Luck. Regards, Bill.
 
Ditto on what Mr Leeper wrote. Brownells sells preground square threading bits, or they used to. Learn to grind your own, it is very impowering. The wheels that come on your typical 6" tool grinder are not meant for h.s.s. grinding. Lee valley will sell you some good ones meant for tool steel. While you are there check out their tool grinding rest, its not bad. A proper rest makes grinding bits for the lathe or shaper a lot less intimidating.
 
When I cut square threads I always grind my tool width undersize. I then cut the thread to the proper depth and the to make the thead wider I advance the cutter longitudinally (is that a word) via the compound rest a few thou at a time.
 
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