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Lathe jaw truing

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  • Lathe jaw truing

    I've seen a lot about truing the inside portion of lathe jaws that hold a cylindrical piece but what about the face of the jaws?
    I have a turning that looks like a face plate.
    I'm checking the run out of the face of this piece and indicated the surface of the jaws where it sits against.
    I'm seeing like -.0003" on one jaw and am wondering if it's of any value to grind them closer than that?
    I couldn't detect any loose movement pushing the jaw back toward the chuck so I'm thinking it should grind in well?
    Len

  • #2
    The wear we call "bell mouthing" where the internal edges of the jaws won't evenly grip a piece of stock is due to wear on the gripping edges as well as wear in the slot of the jaws where they rub in the channels of the chuck body. If that wear is going to result in the jaws tilting out a little and if not 100% even will see one jaw sticking out further than the other in this manner.

    I'd say tht if you have the tooling already setup that you may as well touch up the radial faces a bit at the same time so that using the faces will result in a good and true fit.
    Chilliwack BC, Canada

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    • #3
      I would only turm my attention to the face of the jaws after grinding the insides true. The tensioning ring will get in the way of any face grinding. Then clamp on to a quality piece of cylindrical bar, like a drill blank, or long milling cutter shank. Then retest the face runout. There is no guarantee that the jaws will repeat perfectly if they are loose in their slots in an axial direction. Perhaps pushing the jaws towards the chuck body while tightening them might give repeatability. Probably, when setting up to grind the inside surfaces, the light loading provided when you tension them will take care of any tipping in their slots.

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      • #4
        Personally, I wouldnt be concerned with 3 tenths on the face if i'm interpreting this message correctly. Most people dont work to tolerances that tight

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        • #5
          I have taken very light skim cut on jaw faces once or twice on my lathe. Mostly to get rid of dings and dents.
          But .0003 " sounds like nothing in this context.
          Location: Helsinki, Finland, Europe

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          • #6
            Thanks.
            I just never heard of anyone doing it.
            Add that to the list.
            Len

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