My first attempt on chambering and turning a barrel

[nanuk]

Now for the setup trick...once you get the barrel in place, and threaded..take a hose clamp, and clamp your test indicator to the threaded stub,put a dead center in the tailstock, then move your tailstock up close enough to touch the indicator needle to the angle on the dead center, tighten the tailstock down...then rotate the barrel so the indicator needle is indicating the dead center in the tailstock. Get the runout down to .000..what you find may may make your jaw drop.

Bill

Just a question Bill, I have read where some lathe's tailstocks actually come in a bit high, not true centered to the headstock. (to allow for wear??) I believe I have read this on "Practical Machinist" site.

anyways, if this difference could be measured, I assume it could be added/subtracted to the indicator reading to ensure a true bore?

[JIMinPHX]

It's been my experience that the tailstock on every lathe is a little different. Also, you sometimes need to indicate them & tap them in to center if you are doing precision work. They often have front to back adjustments on them, but seldom have up & down adjustments on them. Each lathe is a little different though. I have recut & shimmed tailstock housings before to bring them back to where they need to be. A little rust under them or a little swarf on the bed will cause them to rise a little sometimes.

[jim147]

I'm confused on your tpi. I understand you had problems with the lathe setup to start. I've had things not work out right myself.

Was this a Rem 700? What tpi did you wind up with on the barrel?

20 was the wrong lever, I get that. But I saw 4 and 8 listed. Isn't a 700 16 tpi?

I mean no offense and think I'm missing something. I would just like to learn a little more about barrels.

jim

[andremajic]

I'm confused on your tpi. I understand you had problems with the lathe setup to start. I've had things not work out right myself.

Was this a Rem 700? What tpi did you wind up with on the barrel?
Once I was finished, it was 16 TPI. It started out at 20 TPI because I was using the power feed lever instead of the half-nut.

20 was the wrong lever, I get that. But I saw 4 and 8 listed. Isn't a 700 16 tpi? I tend to write a bunch of stuff that might be irrelevant to the post, mainly for my own info to reference later. 4 and 8 were the lowest settings that I could go while using the power feed and 20 TPI was the lowest result I was getting. (Hope that makes sense.)

I mean no offense and think I'm missing something. I would just like to learn a little more about barrels.

I'm not offended by questions or even critisism. The correct setting that cut 16tpi with my particular lathes quick change gearbox turned out to be B-4, using the half-nut to engage the carraige. Once the thread depth was correct, I am able to now screw the action on with a slight amount of resistance. AAA thread fit!

jim

I hope what I wrote helps make sense.
Andy.

[jim147]

I got you now.

Thank you

jim

[MBTcustom]

Hey fellas, I'm just a machinist so I don't know a whole lot about gunsmithing but I do know this: three wires is the most accurate way to measure threads, it does not make accurate threads. A thread is a way to fit two things together and as such its best to cut the threads to match the threads you are trying to mate, either inner or outer. This is how I thread a barrel. I could cut threads perfectly according to the wires, but depending on what some other yay-who (god knows where and god knows when) did, the threads may be loose or tight (loose is far more common). By custom cutting the threads to the action you can insure a perfect fit on even the most beat-up old military actions.
One other thing I will say is that a thread file is pretty cheap and it is very useful for creating accurate threads. So many times I have been sneaking up on the perfect PD and all of a sudden, my tool decides to bite the thread and then you have a real problem. The thread file does three things,
1 it cleans all the burs off the threads so you don't get false readings from the mating part when checking for fit.
2 it changes the finish on the surface so that your tool will remove a few ten-thousandths without riding and creating push-off that will bite you later. 3 when it gets down to the last couple ten-thousandths of an inch, you can polish that PD right in with the file.

[Cap'n Morgan]

As Goodsteel says, three wire measurement is the correct way to measure the pitch diameter of a thread. That said, there's no need to worry about the fit being a little too loose. A 60 or 55 degree thread is pretty much self-centering once the barrel is pulled tight. If anything, a loose fit may actually improve concentricity, and strength-wise it hardly matters at all.