Threads on Savage Bbl's ?

[Baddog0302]

C R S has struck and I can't find my link to the topic, I do remember that they are the same TPI the "large" is just a bit larger that the standard.
My question is , and a half ass good machinist cut a large shanks threads down, then re cut the threads to fit a standard action.
If I can find a large shank 308 chambered bbl and have it re cut I want to make a cast bullet shooter and want the 1-12 twist instead on the 1-10 on standard varmint bbls ??

 

[Erik Cortina]

Yes, it can be done. The small shank is smaller than the large shank small diameter.

 

[Concha]

The barrel nut is longer on the small shank threads. The best aproach in my opinion, is to completely turn down the old barrel thread and the larger barrel diameter to the finish diameter of 1.055. There will stll be a small portion of the old thread remaining. The machinist would then engage the lead screw and stop the chuck. He would the pick up the old thread and proced to cut the thread to the new length.

 

[Erik Cortina]

The barrel nut is longer on the small shank threads. The best aproach in my opinion, is to completely turn down the old barrel thread and the larger barrel diameter to the finish diameter of 1.055. There will stll be a small portion of the old thread remaining. The machinist would then engage the lead screw and stop the chuck. He would the pick up the old thread and proced to cut the thread to the new length.

There will be nothing left of the threads when you turn the large shank down to 1.055"

 

[Concha]

There will be nothing left of the threads when you turn the large shank down to 1.055"

Even better. You remove .065 to go from 1.120 to 1.055. Thread depth of .032-035 per side. I assumed the possibity of a faint line. Maybe not. Symantics to me.

So to complete the process measure an older small shank length of threads and copy that dimension

 

[Nomad47]

If you remove .065" material, you will be in trouble. Removing half that will get you to 1.055".

Maybe you meant .065" total (for the two sides when measuring diameter). I just didn't want you to ruin a barrel. You can always take more off.

 

[rwk]

Go to savage shooters, you will find the answer.

 

[Erik Cortina]

It's not hard guys. 20 TPI ==> 1/20 = .050"

So the small diameter on 1.120" 20 TPI is 1.070", plenty left over to turn to small shank of 1.055" x 20 TPI

 

[Concha]

If you remove .065" material, you will be in trouble. Removing half that will get you to 1.055".

Maybe you meant .065" total (for the two sides when measuring diameter). I just didn't want you to ruin a barrel. You can always take more off.

Who mentioned removing .065 per side. My thoughts where on a 16 TPI not cleaning up but it was simply a mental error. following what I said previously would not have resulted in anything being scrapped. There was never any suggestion or direction to undercut the barrel below 1.055. There was no direction to remove .065 per side. Removing .065 is just that. Removing .065 per side would be removing .130 on diameter. One feeds in per side one removes stock on diameter. Stating that there would be a "witness" of threads had no implication of being undersized...quite the opposite. If you have never run a machine you might not grasp that concept.

The actual thread depth on diameter is not .050 but is .065(.032 per side) from a 1.062 nominal dimension

 

[Erik Cortina]

Concha, Savage uses 20 TPI, not 16 TPI. So thread depth is .050" I'm pretty sure.

 

[Concha]

Yes savages use 20 tpi.

1/20 = .050(pitch), 1.299(constant) x .05 = .06495 double depth

Look next to the number 20 on the right side of the tool.

 

[Concha]

The .050 is the distance from one tip of a thread to the next one on 20 tpi. Lets work out remington threads and check my formula. They are 16tpi.

1/16 = 0.0625. .0625 x 1.299 = .081 Check this against the double depth reference on the tool.

Looks like the formula works.

The difference is that savage threads are .0075 smaller than nominal.

 

[Erik Cortina]

You might be right, I'll look at my machinist handbook for the answer.
Bottom line is that you can take a large shank down to a small shank.

 

[Erik Cortina]

Machinery's handbook 29th edition.

Class 3 fit for 1 1/16" - 20 TPI UN
Tolerance = 0.0000"
Major diameter = 1.0625"
Minor diameter = 1.0080"

1.0625" - 1.0080" = 0.0545", which is thread pitch + clearance.

 

[SinMan]

Plenty of meat left after it is turned down. I do probably 2-4 a month, some months more.

 

[Concha]

I did a test piece using both formulas and found that the pitch diameter was correct using thread wires for class 3 threads. the formula I provided. So I did a little research and found that the formula for UN threads is is due to the shape of the tool. it is flat or slightly rounded requiring less infeed because of the root of the thread. A little more research found that there is a possibility that Savage uses a UNJ which is mill spec and has a large radius in the roof of the thread. Stands to reason due to the high presures and potential stress risers from a sharp threading tool like the one I use. I will discontinue using threading inserts with a 0 radius and will find some of the UNJ inserts. I am glad I got into this debate.

Sorry for hijacking the thread.

Fish

 

[Baddog0302]

THANK YOU, All for your input, Now to find a Savage 308 bbl with the 1-12 twist