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Thread: Cutting a good crown

  1. #1
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    Cutting a good crown

    I am having a lot of trouble with cutting a good crown. I have used a boring bar with carbide insert, I have also tried a hss boring bar and both are pushing a burr into the bore. Does anyone else have any ideas? If you grind your own, would you mind posting a picture?
    Thank you.

  2. #2
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    I would not use a boring bar to cut a crown.

    The proper method is single point facing with a sharp, positive rake tool ground from either a cemented carbide or high speed steel.

    I use a 1/2 inch shank 883 grade cemented carbide ground with a curved chip breaker and a very slight nose radius, just enough to keep it from chipping.

    I run it at 1000 rpm and hand feed, the final just taking .001 inch from the face..

    http://benchrest.com/attachment.php?...1&d=1488857111

    The best way to cut a convex crown such as found on factory barrels is to use a sharp form tool to cut the convex shape, and then sing point a small counterbore just a few thousandths larger than the groove diameter to insure you have not pushed metal and formed a burr and also maintain the cosmetic appeal of the crown.
    Last edited by jackie schmidt; 03-06-2017 at 11:37 PM.

  3. #3
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    Some of the solid carbide micro boring bars work excellent if your finish pass starts in the bore and works it's way out.

  4. #4
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    Quote Originally Posted by Rubicon Prec. View Post
    Some of the solid carbide micro boring bars work excellent if your finish pass starts in the bore and works it's way out.
    Why use a boring bar for a facing operation??

    .

  5. #5
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    Quote Originally Posted by JerrySharrett View Post
    Why use a boring bar for a facing operation??

    .
    I like a ~60* crown, cut to just past the depth of the grooves - for this the mini carbide boring bars are excellent.

    Edit: got my crowning threads confused...

    GsT

  6. #6
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    I too like using a micro 100 boring bar for the crown. It's sharp and makes a super finish. I use a 3/8" shank and the shortest bore depth they make. I just simply angle the tool post so it makes roughly a 45 degree angle for my recessed crown. They also make nice tenon counter bore and cones. If you want a pic...I can post one up
    Last edited by DSM; 03-07-2017 at 12:20 PM.

  7. #7
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    Quote Originally Posted by JerrySharrett View Post
    Why use a boring bar for a facing operation??

    .
    Because it works great and allows you to reach into the bore.

    Quick demo video: https://www.facebook.com/77279175609...8941061141915/

    Finish directly from the machine. No polish whatsoever.



    Edit: I also use that same boring bar to finish the counterbore although I use an insert boring bar to rough it out.

    Last edited by Rubicon Prec.; 03-07-2017 at 11:17 AM.

  8. #8
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    I might be wrong, but I would venture that the OP does not have a full CNC capable machine that he is doing his barrel work on.

    Your procedure is totally impractical for the multitudes of Hobby/Gunsmiths who are working with small 13-14 inch manual machines doing just a few barrels to satisfy their own, or perhaps a few friends, needs.

  9. #9
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    Quote Originally Posted by jackie schmidt View Post
    I might be wrong, but I would venture that the OP does not have a full CNC capable machine that he is doing his barrel work on.

    Your procedure is totally impractical for the multitudes of Hobby/Gunsmiths who are working with small 13-14 inch manual machines doing just a few barrels to satisfy their own, or perhaps a few friends, needs.
    I did my crowns the exact same way on a 13x40 manual machine for years. I was using Circle M solid carbide boring bars then because I didn't need focused coooant. The ops were the same.

  10. #10
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    Quote Originally Posted by rubicon prec. View Post
    i did my crowns the exact same way on a 13x40 manual machine for years. I was using circle m solid carbide boring bars then because i didn't need focused coooant. The ops were the same.
    ok.

  11. #11
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    This is what I use...



  12. #12
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    [url]http://benchrest.com/attachment.php?attachmentid=19167&stc=1&d=14889286 36[/url

    http://benchrest.com/attachment.php?attachmentid=19168&stc=1&d=14889287 26

    http://benchrest.com/attachment.php?attachmentid=19169&stc=1&d=14889289 39

    Cuts off the back side with Lathe in reverse. The reason?? I accidentally ground the tool wrong.
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    Last edited by jackie schmidt; 03-07-2017 at 07:22 PM.

  13. #13
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    Quote Originally Posted by Rubicon Prec. View Post
    Because it works great and allows you to reach into the bore.









    you do know the radius or chamfer on the back of chamber is kind of a bad thing.....

  14. #14
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    Quote Originally Posted by geo.ulrich View Post
    you do know the radius or chamfer on the back of chamber is kind of a bad thing.....
    On certain cartridges, yes. On most of the cartridges I work with, it's still safe and allows for reliable feeding from a magazine.

  15. #15
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    Last edited by jackie schmidt; 03-07-2017 at 10:13 PM.

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