Muzzle threading help needed.

[atunguyd]

Andre, I don't get how that will work work threading to a shoulder. Without a relief against the shoulder how do you feed your cutter in to start each pass?

 

[Andre]

Andre, I don't get how that will work work threading to a shoulder. Without a relief against the shoulder how do you feed your cutter in to start each pass?

Well........In my opinion you should always put a little relief at the end of the thread. You can never get the thread backed up all the way into the shoulder, and if nothing else it gives it that "Professional" look.

 

[Stob]

6literZ, It looks to me like the threads need to be cut deeper in your second pic. A little flat on the top is OK, but that looks like a lot. Is the OD right? On the dial indicator, you have the mount on the chip pan. For that use as a means of when to stop the thread, it is probably OK even though it's wobbly. What about mounting it on the headstock to the left in a horizontal position? Otherwise a simple mag mount can be used as Dave said above. I still don't like relief cuts, every brake I have seen has the thread relief already cut in the brake itself, so making another relief on the barrel is redundant. Keep on practicing!

 

[6literZ]

Practiced a .578-28 thread pattern today, although I've come across conflicting info. AAC thread pitch diameter is .5539 +/- .001 and Silencer Co specifies .5546 +/- .001. And the kicker is my threaded FN pistol I measured at .5515!!
I have checked the zero on my mic, and made sure the correct anvils are in place.

So I was concerned because the adapter I'm using is SilencerCo and even when I'm cutting to .5539 pitch dia it is tight threading on.

I will have to check my HSS bit profile to make sure all is well, but I believe it should be as I just have sharpened it.

 

[Holescreek]

The min/max for a 2A class thread is .5500/.5537" and the max for a 3A class is .5548" Personally, I think that 99.9% of manufacturer's specifications are made up on the fly with the first number seen in a book. Going for the max or above allows the threads to be "worn in" together the first time they make contact I guess.

 

[6literZ]

Thanks for the response, I have been renting the machinist handbook from the library, but had to return it. Looks like it's time to pick one up.

 

[Holescreek]

I have a couple of them but never crack them open anymore. One is from the mid 1940's and the other is from the 60's and there's no difference that I can find between them (and it takes forever to find what I'm looking for). I bought a computer program called "ME ThreadPal" that allows me to see everything with a couple mouse clicks and for non-standard threads (like the .578-28) I can input the spec. and it calculates the data instantly.

 

[6literZ]

I will have to look into that after seeing the price on the books. D:

 

[Brandon1]

I picked one up off ebay for 17.00 delivered.

 

[epanzella]

I too use a 2 inch dial indicator on my carriage feed. When threading a barrel I don't like to use a relief groove if I can help it. I grind my 60 deg tool so that the point is off center, with the short side being the dimension of the relief I need to the shoulder. I kill the power .070 short and it coasts to within .020 of the shoulder . I thread right up to "zero" by hand. The thread just "ends" with no weakening relief cut.