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Grinding jaws removed from lathe chuck

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  • Grinding jaws removed from lathe chuck

    I would like to try to re-grind the jaws from a 6" universal chuck using a T&C grinder. The jaws are worn and I'd rather try to use some method of indicating the jaws to determine the amount needed to come off each one and then grind them after removing. I was going to run a grinder inside the chuck so I do have a ring that I can put in the very back of the jaws to preload them.
    If this seems feasible what would be the best way to indicate the individual jaws?
    I have several indicator types but I am not sure that running an indicator inside the chuck using the carriage will be accurate.
    Thanks
    Howard

  • #2
    I think trying to indicate the jaws and then removing them to grind them would be problematic and more work than grinding them in place.
    The preload on the jaws is an important factor in the run out of the jaws in the chuck. I wouldn't suggest grinding them separated from the chuck and without a load on them.
    Mount the ring in the back of the chuck for obtaining the preload and then mount a die grinder in the tool holder. The pencil style pneumatic die grinders work well for this as you can usually use a boring bar mount (you make have to make a bushing for the grinder to fit snug).
    Touch up the jaws until you have a uniform grind pattern across all the jaws. I would first mark the jaw surfaces to be ground with a black marker over the entire contact surface. When the black has disappeared on the jaws you are done. Shouldn't take very long.

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    • #3
      I tried this, I have my doubts it'll be viable too. In my case the jaws had been ground so many times in the past they had lost their vee profile, so I reground the profile back to a vee in a jig in my surface grinder and ground them square to what I expected them to be. On mounting in the chuck, they were significantly off true due to wear in all the components and I had to final grind in situ with a toolpost grinder.
      Now I have a chuck that runs really true at the ring diameter, but nowhere else, It needs converting into a boat anchor or weight for something when I get the money for a better one.

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      • #4
        You don't need to do any indication or measurement when you do the job in situ. Just set up the jaws with the ring, and set up a toolpost grinder that can only reach one jaw. Do each jaw in turn by turning the chuck. At the end of the day, you'll be able to turn the chuck without even kissing the stone. That's when you know the job's done.
        Richard - SW London, UK, EU.

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        • #5
          Originally posted by MrFluffy View Post
          Now I have a chuck that runs really true at the ring diameter, but nowhere else, It needs converting into a boat anchor or weight for something when I get the money for a better one.
          I'm assuming you have a 3-jaw chuck. Have you always used the same chuck key location for tightening? If so, that is one problem source for non-centering on other diameters. I always just snug the jaws first and check with a DI or DTI and retighten from a place that is nearest to the high spot. End result is nearly always dead on, while if only tightening from the so called 'master' location.
          Amount of experience is in direct proportion to the value of broken equipment.

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          • #6
            Originally posted by challenger View Post
            I would like to try to re-grind the jaws from a 6" universal chuck using a T&C grinder.
            A chuck needs a bit of play between the jaws and their slide surfaces, and by the time the jaw get worn to the point that you want to true them up, this play can be greater as well. This will cause the jaws under loading conditions to tip back a bit at their ends away from the lathe axis. For that reason, grinding outside the chuck would actually end up on somewhat of a taper to allow the jaw to grip fully when assembled.
            Grind them in place as discussed. Far better results should be found.

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            • #7
              Originally posted by Jaakko Fagerlund View Post
              I'm assuming you have a 3-jaw chuck. Have you always used the same chuck key location for tightening? If so, that is one problem source for non-centering on other diameters. I always just snug the jaws first and check with a DI or DTI and retighten from a place that is nearest to the high spot. End result is nearly always dead on, while if only tightening from the so called 'master' location.
              Not to derail this thread, but the chuck rattles like a set of castinettes and you can physically wobble the jaws in the slots and measure the play with a normal ruler its so worn. Its some anchient cushman that I inherited worn out with my very first lathe so its time I turned it into a welding fixture holder or something.
              Gary, you got that right, the bellmouth on my jaws was extremely significant. I would estimate about 10deg off parallel.
              The above just reinforces do it in situ. I'm passing on my experience from trying it anyway

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              • #8
                The reason I inquired is because of all I've read about the jaws being OK for one diameter after grinding in the chuck. It seems preloading and grinding in the chuck puts a groove in each jaw instead of a flat.
                I suspect I will live with it and start using 4-jaw chucks when I need to mount something accurately.
                Thanks
                Howard

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