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Thread: A situation I have seen several times:

  1. #16
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    Question for Jackie

    Quote Originally Posted by jackie schmidt View Post
    The thread and the tenon shoulder should always be machined on the same setup.
    Have a question for Jackie . How do you cut the shoulder when you set a barrel back with the threads already cut?

    Thanks Chet

  2. #17
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    I turn the tenon .010 short, I grind a right facing tool, with a point that is ~80 degrees (acute), set the compound rest at 90 degrees and plunge into the face 0.010" out from the tenon 0.010" and slowly draw out watching the cut carefully to make sure it's a proper facing. I do the same thing to a muzzle thread, because i want the brake to barrel fit to be invisible.
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  3. #18
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    Quote Originally Posted by Bnhpr View Post
    I turn the tenon .010 short, I grind a right facing tool, with a point that is ~80 degrees (acute), set the compound rest at 90 degrees and plunge into the face 0.010" out from the tenon 0.010" and slowly draw out watching the cut carefully to make sure it's a proper facing. I do the same thing to a muzzle thread, because i want the brake to barrel fit to be invisible.

    Ben, when you are indicated and before your cut, is the old shoulder perpendicular to your bore?

  4. #19
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    Something quite like this can happen quite easily when indexing or "timing" barrels IME. Not that the threads or shoulder are out of alignment, but that the undercut at the shoulder can be left at an interference..... this need be checked carefully. For instance I did one today where my initial setup, tenon offset/length resulted in the barrel tightening up just past where I wanted it. This required that I rotate the barrel nearly another full turn, advancing it or "lengthening the tenon" about .045 which moves the abutment shoulder the same 45thou down the barrel. I had to remember to widen the chickenout groove 35 thou toward the muzzle.

    Had I not paid attention the barrel would have tightened up against the threads instead of bottoming out and crushing against the shoulder.

    I'm with Jackie re the use of Dykem. If the barrel doesn't wipe the Dykem immediately, as in FIRST THING as soon as it feels somewhat tight, the relief must be extended toward the muzzle.

  5. #20
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    Sometimes the shoulder is cut with the SIDE of the grooving tool.


    .

  6. #21
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    [QUOTE=coyotechet;831581]Have a question for Jackie . How do you cut the shoulder when you set a barrel back with the threads already cut?

    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.

  7. #22
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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.

    Thanks Chet

  8. #23
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    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

  9. #24
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    Quote Originally Posted by JerrySharrett View Post
    Sometimes the shoulder is cut with the SIDE of the grooving tool.


    .
    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.

  10. #25
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    Quote Originally Posted by coyotechet View Post
    [/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.
    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.

    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.
    Last edited by jackie schmidt; 02-17-2020 at 07:48 AM.

  11. #26
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    Quote Originally Posted by Richard View Post
    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
    I thread with standard upright inserts. I also thread straight in.


    http://benchrest.com/attachment.php?...1&d=1581945430
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  12. #27
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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.

  13. #28
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    Quote Originally Posted by jackie schmidt View Post
    I thread with standard upright inserts. I also thread straight in.
    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.

  14. #29
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    Quote Originally Posted by parshal View Post
    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.
    250 rpm, I like the Rigid Dark sulphurize threading oil.

  15. #30
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    Quote Originally Posted by Dave Tooley View Post
    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.
    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.
    Last edited by jackie schmidt; 02-17-2020 at 10:58 AM.

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