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Oh Fu.uudge! Dropped my 4jaw chuck

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  • #16
    On my new lathe, the chucks are almost too big to manage by hand. The 10" 3 jaw is a hassle for me to mount by hand, and nobody I know is going to mount that 15" Rohm 4 jaw by hand. Evan's stick might be sufficient once you get it on the bed, but my large spindle bore would mean you need a 2.25" stick to get the chuck near centered (with jaws snug). So I made a cradle for the 10" from 2x4 scrap. Cut and nailed (no contact) it together with glue, then sealed it with paraffin wax. Now the 10" is easy to mount and remove, just plop it in the cradle and slide onto the spindle. I'll need a crane of some sort (or some robust helper) just to get the 15" onto the bed, so no cradle for it yet...
    Russ
    Master Floor Sweeper

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    • #17
      Originally posted by tattoomike68
      A cracked chuck says" I will hit you in the face with 20+ pounds at 60 MPH"

      send it to the foundry gods or use it on a rotary table where its doing low RPMs.

      you can weld it up and use it for low rpm work, I tend to machine faster when using a 4 jaw but that chuck is no longer safe.

      By my calculations, with an 8" chuck revolving at 500rpm (my lathe's max), that chunk is moving at about 11.89 mph. (8 X 3.14 X 500 X 60 = in/hr; divided by 12 = ft/hr; divided by 5280 = mph) I'd guess its weight at no more than about 4 oz.

      While the chunk is in place there is no significant out-of-balance issue.

      I certainly agree, it's not as safe as it used to be. But I don't think it's any great catastrophe waiting to happen either. Tho it does bear watching and exercising caution.
      Lynn (Huntsville, AL)

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      • #18
        Wont the crack get stressed when you tighten the jaws?

        New chinese 8 inch 4jaw, independant is $79 from shars.com
        D1-4 mounting $155
        Who cares about the runout because its independant anyways.

        self centering 4 jaw $129

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        • #19
          Originally posted by ahidley
          Wont the crack get stressed when you tighten the jaws?

          No, where this crack is located I don't think it has any bearing on the structural integrity at all. ...or certainly not much anyway.
          Lynn (Huntsville, AL)

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          • #20
            Of course the bad thing about cracks is that they propagate. . . It's not good in this case but in some cases crack points are drilled to increase the crack tip radius beyond which they want to propagate at the loads encountered. On other types of parts, an insane surface finish is specified so that there are no imperfections in the surface to cause stress concentration. Vibration and other intangibles can also cause cracks to grow.

            The crack will be stressed by tightening the chuck. It will also be stressed by cutting forces since these put a torque on the chuck. The forces that we understand might not make the crack grow but the forces we don't anticipate could be a day ruining experience. Just remember what it's like when you get a chuck key thrown at you and imagine how it would feel if the entire chuck (or half of it) got thrown at you.

            In fact, by my calculation, that chuck spinning at 500 rpm's is storing 150J or about the energy of a .22LR Rifle round** While it may take a good shot to kill you with a .22 rifle, Murphy has been known to be a good shot on our worst days.See the energy content of rifle bullets at http://en.wikipedia.org/wiki/Muzzle_energy.

            Do you really want to wonder where this energy will go if the crack liberates it suddenly?

            **
            E=I*w^2
            I=m*r^2/2
            w=500rpm*(1min/60seconds)*(2Pi Radians)/revolution
            Assume chuck mass=22 kg (50 lbs)
            Radius as given at .1m (8 inch diameter)

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            • #21
              lynnl, from the way you describe it a good weld shop could safely weld it and you would never have an issue with it. As you describe it the crack is not in a loaded or sensitive area.
              It's only ink and paper

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