Muzzle threading help needed.

[6literZ]

Hello,

I've recently purchased my first lathe; a Grizzly G4003G, which I've only completed a few simple projects such as a few brass tops and a widget with threads and knurling to familiarize myself with the machine.

I'm starting to get more serious and tool up for my current project of building a 45acp Mauser and would like to practice threading on some stock to get it perfect before I thread the muzzle on the Mauser 45acp barrel.

I've been looking at AAC's thread specs and am stumped on how with a manual lathe this pattern can be achieved due to the lack of a relief cut next to the shoulder. Even if threading were done in reverse I can't picture how the threads would be started without the relief.

If anyone has any suggestions on this process please let me know, I'm also open to any suggestions for tooling for internal threading to thread inside 1/2" diameter threads, as well as external threading tools. I currently have ground a 60* HSS bit.

Here is the drawing of the thread pattern for a 30 cal showing no releif next to the shoulder.



Thanks in advance!

 

[Holescreek]

I always put a relief cut in next to the shoulder the width of my cut-off tool (.123") and make it to the diameter of the large end of the minor diameter tolerance. That way when the tip of the tool touches it I know it's time to start measuring thread pitch. That threading up to a shoulder thing is for specialty equipment and/or masochists.

 

[Rick Leslie]

Agreed. Threading to a shoulder manually is for the birds. A relief cut will not change the way your device threads on the muzzle since it will torque to the shoulder. Now I have threaded manually to a shoulder before when it was necessary, but you have to go really slow and have no outside interruptions. Cut the relief like Holes said and happy threading.

 

[spitfire_er]

I've threaded gun barrels on an old Clausing 14" with a hand clutch like that. You have to throw the clutch ( or kill the machine) 1/4 to 1/2 way around before you hit the end of the thread. Then you have to turn the chuck by hand to finish the last bit to the end of the thread. Only reason I did this was if I were planning to set the chamber back in the future, I could just cut off 1/2" or so, pick up the old threads and rechamber. Saved on barrel length. You can't do that if there is a relief cut.

Not as easy as a relief cut, but it's one way to skin a cat!

 

[dave2176]

For internal threads that size I use a left hand carmex insert holder. It is style SIL size 10 (IIRC) I found on ebay. Shipped from Israel. It barely fit a .459" hole for the 1/2-28 thread I needed but got it done. I've seen smaller sizes on ebay at times too. To use a left hand tool to make a right hand thread you run the lathe in reverse and thread from left to right. This eliminates the possibility of a crash in a blind hole.

Dave

 

[Stob]

Sorry, but I don't see the issue with threading to a shoulder. Do it all the time threading barrels. I know many people cut relief grooves, but I don't. I use a Kennemetal Top Knotch holder and insert, very narrow, the insert is right along the left side. You can thread to within .050 to .060 tho' of the shoulder.

I've had a DRO on my lathe before, but threading and watching the numbers it too much for me. I use a simple 2" travel dial indicator and a mini mag mount. I made a bracket to clamp on the ways and I can slide the indicator back and forth. When I set up to thread a barrel, I set the tool up to the shoulder where my thread ends and set the indicator to zero, against he carriage. So all I have to do is thread and watch the dial come back to zero, pull the half nuts and back out the cross feed at the same time. Very easy, repeatable, and I've never hit a shoulder.

You can do internal threads the same way. I don't do supressors, but for muzzle brakes, I inside thread and the relief is in the brake after I thread.

FYI, don't rely on the barrel OD, indicate the groove diameter the turn the barrel down and thread. You have to be centered in the bore.

 

[Rick Leslie]

For threading the muzzle a relief won't matter. For a beginner, the relief is a good way to go in my opinion. And I've threaded more barrels than I care to remember over the last 35+ years and making a relief cut on the shank hasn't been a problem either. There are as many ways to thread as there are machinists I believe.

for internal threading, I turn the tool upside down and thread on the back side of the ID. Makes it easier to see, plus the muscle memory from ID threading remains the same. You're turning the cross slide and compound the same direction as OD threading. Plus the tool is cutting on the leading edge, same as OD threading and the chips fall away from the cutter, not on top. It just seems to work better for me. Many advantages.

Now for threading the 1/2-28 muzzle device ID, I would simply buy a tap. I know it's cheating, but they are inexpensive and much easier.

 

[MarkStephen]

I've been looking at AAC's thread specs and am stumped on how with a manual lathe this pattern can be achieved due to the lack of a relief cut next to the shoulder.

You just simply need to add this to your lathe - http://www.hobby-machinist.com/showthread.php/20196-Threading-at-400-RPM

)

Mark

 

[6literZ]

Wow!!

That is beautiful!
I have to do that!

And much cheaper than a Hardinge HLV, but I still want one.

 

[Stob]

If you cut a relief in a barrel tenon, and ever want to set it back to freshen the throat, you ave to deal with the cut. If you simply stop the thread, then it is easy to pick up the thread and go. Or somone wants to go Ackley the setback is easy.

I know most peple don't set barrels back, but in the benchrest game, it's done often, especially if one does their own work. To pay a smith to set back a barrel isn't always cost effective.