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Thread: why cut very sharp inside corners ? ( tenon/shoulder)

  1. #1
    Join Date
    Dec 2017
    Posts
    199

    why cut very sharp inside corners ? ( tenon/shoulder)

    From another thread i saw this:

    "I gotta' ask..... HOW do you guys do it, the one single tool to face and set the tenon/shoulder???

    I've got a barrel for a Panda in the lathe right now and that corner at the shoulder has about a 00.00001 relief radius. I'm using a tool looks like a knife blade tip to get in and clean up for a solid seat and I have nothing in carbide that's even CLOSE to a tight enough radius. And the typical surface ground recoil lugs from PTG are also often basically knife-edged at the corners.... "

    and i gotta ask

    Why produce a stress riser if you do not have to ?
    Why not put a radius on the face of the receiver or recoil lug, and skip putting a stress riser on the bbl ?
    ( Yes i will admit i have never seen a bbl fail at that point).

  2. #2
    Join Date
    Feb 2006
    Location
    California...unfortunately
    Posts
    581
    Quote Originally Posted by retired View Post
    From another thread i saw this:

    "I gotta' ask..... HOW do you guys do it, the one single tool to face and set the tenon/shoulder???

    I've got a barrel for a Panda in the lathe right now and that corner at the shoulder has about a 00.00001 relief radius. I'm using a tool looks like a knife blade tip to get in and clean up for a solid seat and I have nothing in carbide that's even CLOSE to a tight enough radius. And the typical surface ground recoil lugs from PTG are also often basically knife-edged at the corners.... "

    and i gotta ask

    Why produce a stress riser if you do not have to ?
    Why not put a radius on the face of the receiver or recoil lug, and skip putting a stress riser on the bbl ?
    ( Yes i will admit i have never seen a bbl fail at that point).
    Retired,

    I don't. Not that I'm worried about the barrel failing at that point (which I think is highly unlikely), but a wee plunge with a tight radius cutting tool would take care of any barrel to action/recoil lug fitting issues. And as I'm generally working with a freshly trued 700, I have to open up the recoil lug to accommodate the oversize barrel tenon. Whilst the recoil lug is in the lathe or mill for this procedure, I put a chamfer on the barrel side of the recoil lug to provide clearance for the radius.

    Works for me.

    Justin

  3. #3
    Join Date
    Feb 2003
    Location
    VA
    Posts
    909
    The only recoil lug I've seen with a radius cut inside is for an Ellesio (sp) tube gun. Smart!

  4. #4
    Join Date
    Jan 2015
    Location
    Greenwood, Ca
    Posts
    128
    As someone that breaks parts, I try to design with limited stress risers in just about everything I do. I do agree that a chamfer or radius on the lug/receiver face is the proper way to do it, when looking at it form minimal stress concentration standpoint. That said, this joint is so over built and will never, ever fail from fatigue. This is one of those items that each builder should do what they feel looks best and works best for their set up.

  5. #5
    Join Date
    Feb 2003
    Location
    Houston, Texas
    Posts
    7,020
    Searching for problems that do not exist.

    This is the first cousin to finding solutions to non existent problems

  6. #6
    Join Date
    Apr 2006
    Location
    Kentucky-Home of the Kentucky Wildcats
    Posts
    2,008
    Quote Originally Posted by jackie schmidt View Post
    Searching for problems that do not exist.

    This is the first cousin to finding solutions to non existent problems
    Agreed! I've been having to deal with some of that today, myself.

  7. #7
    Join Date
    Dec 2003
    Location
    washington.........STATE that is.
    Posts
    9,557
    BUT....

    I don't WANT a radius per se..... shoulders are small enough as it is and getting a high-torque join without distorting something is paramount so I LIKE the tight corners (stress-risers smesh-risers) because it maximizes my abutting surfaces. I like to under-draw just a quarter-thou, a barely visible hair of a cut like maybe back off a teeensy fuzz-lick on the final outfeed just to ensure (hope) that when I smooosh that joint tight it's got nice even pressure acros't it's face. So I love the look of that thar carbide bit thar.... be get me some, cuz I'm sick of burning the stropped razorey edge off'n my HSS tips.

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