Stock slipping back in the chuck. - Page 2
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  1. #21
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    crank the chuck pressure up past max
    cut more grooves in jaws to get less surface contact
    and increase more pressure per tooth
    I also use a carbidizer which i'v had for years and it leaves just about .0002 of carbide but it is enough that it increases the holding power.MSC and Mcmaster used to carry it.

  2. #22
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    A few things I didn't see mentioned yet..

    How is the jaw contact front to back?? Did you bore the jaws straight and now
    they are only gripping in the back, letting the material shift and walk its way
    back into the chuck? Or on the other side, bore with too much back taper and
    the material is only being gripped at the nose?

    Are we at the ends of the travel for the jaws? Where we are grabbing it, but not
    really grabbing it.

    I'm not sure how this would effect things, but is the tool on center?

    Do you have some kind of F'd up tool holder that is setting your insert in some
    way that is creating excess Z- pressure?

    Are you running an insert that is designed for far higher feed than you are giving it?
    The material not flowing properly over the chip breaker, creating excess Z- pressure?

    Almost every time I've had material push back into a chuck, its because something was wrong..

    And a quick story... 41L40 2.25" diameter... Needed to make time, and we were making good time
    running pretty stupid fast, 1000+sfm, .016 or so a rev, .120ish on the depth, sounded like a hail storm,
    steam flying out of the chip conveyor.. It was eating roughers like candy. Had to rotate
    every 6 parts or so. Slowing it down to get even one more part per corner didn't pencil out.

    Everytime I tried to speed it up more, with more feed or depth, it would pull the part OUT of the chuck..
    Never once pushed the part in, always pulled it out. Never pulled it all the way out, but it would
    pull .02 or .03 a pass...

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  4. #23
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    Max pressure on the machine is 2.0 bar, there is a relief set at 2.1bar, so no way to get more pressure without tinkering with that.
    The jaws are gripping evenly, the wet/dry paper was evenly damaged along the whole jaw.
    Tool is on center
    DMF_TomB: Thanks for calculating the pressure, that is quite something, and as you say, when the insert gets dull it pushes like crazy.
    DCLNR holder is pretty standard isn't it ?
    I'll try an insert with smaller radius and see if that works while still lasting. Could off course change to a CCMT insert and see how that works too, just for testing.

  5. #24
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    Quote Originally Posted by Panza View Post
    The jaws are gripping evenly, the wet/dry paper was evenly damaged along the whole jaw.
    Hear this, if the gripping section of the jaws are Perpendicular to the serrations on the back-then you are probably not gripping along the entire surface. If you are then you definitely need more Chuck pressure, regardless of the "relief"(?). Regular lined paper is about .0045" or so, so about .114mm in Milli-metrics. Guessing wet/dry sand paper is double that, it's not giving you an accurate idea of grip. Chuck on a bar without paper or anything, and use feeler gage to get an idea. I usually back taper bore jaws .002" per linear inch.

    Isn't 2.0 BAR around 30 psi? I run around 275 psi max. But I am probably mistaken about that, not sure 30 psi would even move the jaws.

    There are pointy hard jaws available, you want to actually reduce the surface area of the jaw when you are Chucking on Hot Roll, so it bites into the material, because it's inconsistent surface area and diameter.

    R

  6. #25
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    Quote Originally Posted by litlerob1 View Post
    Isn't 2.0 BAR around 30 psi? I run around 275 psi max. But I am probably mistaken about that, not sure 30 psi would even move the jaws.

    R
    I think I must've been mistaken when I said 18bar? I read the black scale witch is in psi and something I can relate to.

    The max recommended pressure is around 275psi so apparently it's 1.8bar? I'll look for sure again today.

    Brent


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