A situation I have seen several times:

coyotechet said:
Have a question for Jackie . How do you cut the shoulder when you set a barrel back with the threads already cut?:eek::eek:

Thanks Chet[/QUOTE

The way I chamber makes it very easy to set a barrel back up exactly the way it came out on the initial chambering. So the threads and shoulder are running true.

Of course, it is impossible to reset a piece EXACTLY in the same position in a machine as it was on the initial machining where the setup was never disturbed. But the way I do it is so close my “tenth” indicator will barely pick it up.
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Jackie

[/QUOTE= The way I chamber makes it very easy to set a barrel back up exactly the way it came out on the initial chambering. So the threads and shoulder are running true.[/QUOTE]

So I think what you are saying is that you use the same bushing around the muzzle end of the barrel in the lathe spindle as you did when first chambering/threading, then you indicate the throat the same as you did the first chambering/threading. If that is correct, then if I indicate a Deltronic pin in the muzzle/crown (.0001 or close) then indicate the throat same as the first time I should come up close to the same as you when setting a barrel back. I also can clock the barrel to the same setting as it had on the first chambering /threading set up to come up with a more accurate set up.
So am I thinking this right??
I am just asking because I trust your knowledge.:rolleyes::rolleyes:

Thanks Chet
 
It all depends if your

running a full profile or a partial profile insert. It's really hard to use a full profile without a thread relief.
A partial profile works best but you still have to be quick on the half nuts.

Richard
 
JerrySharrett said:
Sometimes the shoulder is cut with the SIDE of the grooving tool.


.
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That's what I use in my Haas. I leave .005" to face off on the shoulder and plunge in deep enough to relieve the corner of the shoulder. Some manufacturers spec out a thread relief groove.
On a manual machine I'd use my turning tool. I never cared for a DRO and used a travel indicator. I'd turn the length to within a thou or two. Then on the final pass cutting the diameter I'd face that off the last few thou. Then feed right back in without moving anything to skim cut the shoulder and plunge deep enough to relieve the corner. If I had to cut a full on groove I would plunge pretty deep that gives me a place below the tenon diameter to work from. I could touch it cutting the groove and not affect the face of the shoulder.
To face the shoulder it has to be a grooving tool. A part off blade isn't rigid enough but works in the scenario I just described.
 
coyotechet said:
[/QUOTE= The way I chamber makes it very easy to set a barrel back up exactly the way it came out on the initial chambering. So the threads and shoulder are running true.
Click to expand...

So I think what you are saying is that you use the same bushing around the muzzle end of the barrel in the lathe spindle as you did when first chambering/threading, then you indicate the throat the same as you did the first chambering/threading. If that is correct, then if I indicate a Deltronic pin in the muzzle/crown (.0001 or close) then indicate the throat same as the first time I should come up close to the same as you when setting a barrel back. I also can clock the barrel to the same setting as it had on the first chambering /threading set up to come up with a more accurate set up.
So am I thinking this right??
I am just asking because I trust your knowledge.:rolleyes::rolleyes:

Thanks Chet[/QUOTE]

That’s pretty much it.

One thing I do in the initial chambering is this. Keep in mind, I establish the best chamber I can BEFORE I finish the tenon.

When I finish the chamber, I place my tenth indicator in the middle of the chamber body and make sure it is running dead true. This was established truly straight with the throat, but you can sometimes get a few tenths run out here and there. After this adjustment, (if needed), I finish the tenon, working off of the chamber.

The reason I do barrels this way is as a machinist, the most difficult part of chambering is establishing the chamber in the barrel exactly where you want it. All other operations are just standard machining. So I chamber first, and then work everything off of it.

By the way, I do rough out all of the tenon dimensions before I do the chamber, usually leaving around .010 or so to finish.
 
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Jackie

Do you think it would make any difference if you finished the tenon, less threads, then came back and cut the threads after chambering? Seems like extra work for an adjustment of a tenth or two.
 
jackie schmidt said:
I thread with standard upright inserts. I also thread straight in.
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What speed do you thread with that insert? That insert and holder look exactly like what I've been using. I recently started playing with a laydown carbide insert and I've been getting better threads. Maybe my speed is all wrong.
 
parshal said:
What speed do you thread with that insert? That insert and holder look exactly like what I've been using. I recently started playing with a laydown carbide insert and I've been getting better threads. Maybe my speed is all wrong.
Click to expand...

250 rpm, I like the Rigid Dark sulphurize threading oil.
 
Dave Tooley said:
Jackie

Do you think it would make any difference if you finished the tenon, less threads, then came back and cut the threads after chambering? Seems like extra work for an adjustment of a tenth or two.
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Dave, it’s more of an old habit. I get all of the heavy cutting out of the way, leaving a tad of stock on all critic fits before I final indicate and do the finish operations.

Since the OD fits nothing but air, you are correct.
 
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jackie schmidt said:
Dave, it’s more of an old habit. I get all of the heavy cutting out of the way, leaving a tad of stock on all critic fits before I final indicate and do the finish operations.

Since the OD fits nothing but air, you are correct.
Click to expand...

thanks
I understand old habits. I try and pay attention to the good ones that have stood the test of time.
 
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Pete Wass said:
I have seen at least 4 and mebby 5 rifles that came from more than one Smith with shoulders on barrels that weren't perpendicular to the tenon. How can this happen? Seems practically impossible yet it happened. Barrels don't stay tight long !

Pete
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Let’s say someone chambers a barrel with the current popular method of moving the muzzle around to get two points running true at the chamber end. Then it gets set back a thread by someone setting the barrel up between centers. That shoulder just became out of square to the threads.

I’ve seen a lot of actions that only have one thread cut out at the front of the receiver for thread relief. On a 18 pitch thread that’s just .055” of thread relief. That’s not enough in my opinion unless you want to take a chance of crashing the threading tool into the shoulder. A thread relief groove on the tenon certainly doesn’t hurt a thing and does make it easier cutting the threads. I had an old barrel that I set up for a fire forming barrel cutting about a 3/8” thread relief then rechambered with my reamer. It was uncanny how well it shot when I first rechambered it. Of course, it doesn’t shoot that well now after fireforming brass 100 at a time as fast as you can do it.
 
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More I think about this, you’d have to have some serious misalignment and/or a scary tight thread engagement to not allow a shoulder to lockup evenly.
 
Let's assume all the work was done in one setup. Even if it was done between centers the shoulder would have a uniform angle in relation to the threads. It may not be perfectly 90 degrees but it would be uniform. Assuming the action is perfect, meaning the face and threads were perfect and exactly 90 degrees apart, any deviation from 90 degree on the barrel shoulder would mean either the ID or the OD of the barrel shoulder would make contact. Just might be your problem.
How does it happen. Headstock misalignment, Cross feed either not perfectly perpendicular to the headstock or the ways , tool/work piece flex when facing off the shoulder. I take a plunge cut of a few thou with a grooving tool then slowly feed back out shaving a tenth or two more off with no load. Then there's the action which we all assume is perfect. Many ways this can go slightly sideways.
 
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