Truing up lathe chuck jaws by grinding in place?


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Thread: Truing up lathe chuck jaws by grinding in place?

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    Default Truing up lathe chuck jaws by grinding in place?

    I'm working for a company that has a old Lodge & Shipley lathe with 11-inch diameter, 6-jaw chuck. It's really tough to get a part to not runout badly. You can feel when you're tightening down on a part that the jaws are not all contacting the part surface evenly. I looked into having it rebuilt for them, and was told that for a 6-jaw that size, buying new would make more sense. There's no way they are going to buy a new one at $1,500 to $3,000. I'm thinking about the possibility of setting up some type of grinding tool on the cross slide, clamping the jaws down on a piece of material at the very back (They're 2-5/8" deep/clamping surface) and grinding the jaws in. I suppose to finish the furthest back area where I was clamping down to locate the jaws, I then have to clamp down on a piece out toward the front (already ground area) with a hole through the center where I might be able to reach into the back with the grinding wheel and finish the rear of the jaws. Sound crazy? Anyone tried something like this?

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    Community Moderator Jim Dawson's Avatar
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    Default Re: Truing up lathe chuck jaws by grinding in place?

    Google youtube grinding lathe chuck jaws. There are a lot of videos on how to do it properly (and proabaly a few videos of ways not to do it)

    Jim Dawson
    Sandy, Oregon, USA


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    Member handlewanker's Avatar
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    Default Re: Truing up lathe chuck jaws by grinding in place?

    Hi, once a self centering chuck, be it a 3, 4 or 6 jaw ….whatever.....starts to run out it will always run out on different diams due to wear on the scroll that controls the position of each jaw within the body.

    I have had good results after truing up a 3 jaw chuck by the normal grinding method having used a ring over the OUTSIDE of the chuck jaws...…...the ring had 3 grub screws that screwed down onto the outside of the jaws and so imparted pressure onto the scroll.....same as the internal ring method.

    This will allow you to run the grinding wheel all the way through in one pass.

    To make even the oldest chuck ( or newest cheap chuck) run true after a long life you need to make the chuck a slack fit to the backplate register (.25mm slack) and then when you grip a diam and It still runs out you just slacken off the holding screws in the back plate and bump the body (with a job in it) to make it run true.....retighten after of course.

    The problem with a worn chuck is bellmouthing due to the jaws being worn in their slots and no amount of grinding can cure that problem......it will enable the work piece to be gripped all along the jaw gripping edge but if you always predominantly grip work near the jaw ends this will exacerbate the wear.
    Ian.



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    Default Re: Truing up lathe chuck jaws by grinding in place?

    Quote Originally Posted by handlewanker View Post
    Hi, once a self centering chuck, be it a 3, 4 or 6 jaw ….whatever.....starts to run out it will always run out on different diams due to wear on the scroll that controls the position of each jaw within the body.

    I have had good results after truing up a 3 jaw chuck by the normal grinding method having used a ring over the OUTSIDE of the chuck jaws...…...the ring had 3 grub screws that screwed down onto the outside of the jaws and so imparted pressure onto the scroll.....same as the internal ring method.

    This will allow you to run the grinding wheel all the way through in one pass.

    To make even the oldest chuck ( or newest cheap chuck) run true after a long life you need to make the chuck a slack fit to the backplate register (.25mm slack) and then when you grip a diam and It still runs out you just slacken off the holding screws in the back plate and bump the body (with a job in it) to make it run true.....retighten after of course.

    The problem with a worn chuck is bellmouthing due to the jaws being worn in their slots and no amount of grinding can cure that problem......it will enable the work piece to be gripped all along the jaw gripping edge but if you always predominantly grip work near the jaw ends this will exacerbate the wear.
    Ian.
    so what if you just run the rpm as high as possible so centrifugal inertia provides the needed outward force against the scroll?



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    Member deadlykitten's Avatar
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    Default Re: Truing up lathe chuck jaws by grinding in place?

    hello, i am ok with grinding, i do it on cnc lathes when i craft hard jaws

    about your situation, it may be better to grind only 3 of your 6 jaws, so to eliminate half of your plays; something like consider that you only have 3 jaws ?! if this grinding ends out nice, then grind also the rest of 3 togheter with the initial 3 ... if there is too much play inside your chuck, it may be better to remain at only 3 jaws

    let's hope that grinding will fix it / kindly

    we are merely at the start of " Internet of Things / Industrial Revolution 4.0 " era : a mix of AI, plastics, human estrangement, powerful non-state actors ...


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    Member handlewanker's Avatar
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    Default Re: Truing up lathe chuck jaws by grinding in place?

    Quote Originally Posted by Eldon_Joh View Post
    so what if you just run the rpm as high as possible so centrifugal inertia provides the needed outward force against the scroll?
    Hi, that won't work as the scroll needs to be pushing down on the jaw grooves, also there would not be enough force either.

    When you get wear on the scroll bore diam or the chuck body where it rotates in the chuck body NOTHING will bring it back to life as the scroll can wander around and cause the jaws to do the same.

    Grinding the jaws will only correct bell mouthing but you also need to make the chuck a slack fit on the register to allow it to be bumped back to run a job true.....a few thou is all it takes.

    The scroll will wear on the inner diam and at places on the scroll grooves depending on the diams it gripped most on...……...even the worst chuck can be made to run true with a slack fit to the back plate...….you will have in effect a poor man's GRIPTRUE chuck.
    Ian.



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Truing up lathe chuck jaws by grinding in place?

Truing up lathe chuck jaws by grinding in place?