Chuck jaws not holding workpiece concentric.
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  1. #1
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    Default Chuck jaws not holding workpiece concentric.

    Hi,

    I'm working on this old Takisawa lathe with a SMW hydraulic 3-jaw chuck. After lots of indicating here and there I concluded that it's the jaws that aren't holding the workpiece straight.

    There's something quirky with this chuck because in order for the workpiece to be relatively centered, one of the jaws has to be one notch off compared to the other two, otherwise the piece is noticeably off-center.

    On top of that, the worpiece tilts to one side, enough to max out the dial indicator, like over 45thou.

    I'm not sure if replacing the moving parts would correct this.

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    .045" is a lot for any scroll chuck, even one that is sprung. Do you know that those jaws have a number on each one (1,2 and3) and corresponding numbers in the slots? The jaws have to be in the right slot but I'm not sure if that will help with .045" run out? Try to check that but I think the run out will be more than that if assembled wrong, never checked a chuck after the jaws were installed in the wrong slot so don't know for sure.
    Dan

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    Thanks but the numbers match!

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    chuck may have ground with jaws in wrong.. might try moving them about.. Yes look for bangs and bugs.. The scroll does not have a chip behind it...the whole chuck wobbles ..The lathe nose runs true..

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    SMW chucks are not as tough as most others (Matsumoto, Kitagawa, etc.). I've seen more than one with cracked or broken masters as a result of a crash that the other brands would tolerate easily.

    You really need to tear it down and give all the moving parts a very thorough inspection before trying to make parts.

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    Is it a scroll chuck ?

    Me thinks it will be a hydraulic wedge type, or the one with swinging
    pivots.

    "Off by one notch" are the jaws the ones with .06 serrations ?

    Ring up Worldwide chuck in O-HI-O.

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    Soft Jaws???

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    I'm in agreement on taking that poor old chuck apart and finding whats broke. Have you been running this this chuck/lathe in the machine for very long, If so, you've really beaten up that spindle bearing.....you didnt see that wobbling around in the chuck prior to indicating it?that is a pedal operated hydraulic chuck with .045"TIR, means that jaw is off a notch, or something is surely broked inside?

    or like it was already mentioned, buy some jaws if you want it super accurate and bore them on center of turret.
    Probably time to check that turret out too, I'm willing to bet it is off center to the spindle too!!!

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    OK so I tore it down and it's seriously worn in the "ways" on top of having a piece broken off one of the "masters" !

    I did all kinds of measuring on the turret since that's what the operator was complaining about, even though there was something visibly wrong with the chuck. The turret seems fine.

    Thanks for all the replies. If I can I'll post some photos when I'm off for anyone interested!

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    Quote Originally Posted by Cicame View Post
    Hi,

    I'm working on this old Takisawa lathe with a SMW hydraulic 3-jaw chuck. After lots of indicating here and there I concluded that it's the jaws that aren't holding the workpiece straight.

    There's something quirky with this chuck because in order for the workpiece to be relatively centered, one of the jaws has to be one notch off compared to the other two, otherwise the piece is noticeably off-center.

    On top of that, the worpiece tilts to one side, enough to max out the dial indicator, like over 45thou.

    I'm not sure if replacing the moving parts would correct this.
    Surely nothing less than new guts will.

    Symptoms say it wasn't JUST worn, it was crashed. At the gallop, and HARD.

    SMW has a footnote in their catalog that offers the technical drawings if one asks:

    https://www.smwautoblok.com/media/uploads/hynd_s.pdf

    No assurance it is even remotely worth an attempt at rebuilding.
    Some other used one with a less stressed history probably far the better deal.

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    I don't think a rebuild is an option either... We're set on getting a replacement chuck.

    Coincindentally we recieve a SMW newsletter and apparently there's a trade-in program. It might be a good deal too, we'll see...

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