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Thread: Chuck jaws

  1. #1
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    Default Chuck jaws

    The 200mm 4-jaw I recently fitted to my lathe has been giving me a bit of grief, and it turns out that the jaw surfaces used for gripping pipe/bar (the full length jaw surfaces) are meeting at the rear of the jaws leaving a gap at the front. The gap is 13 thou on one pair, and 15 thou on the other pair.
    Is that considered acceptable? If not, how do I go about fixing this please?

  2. #2
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    I would not consider that acceptable. You could grind them in place with a toolpost grinder, or take them and get them gang ground.

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    Definitely shouldn't be out that much, you'd be losing a lot of clamping force with only point contact..

    I wonder if toolpost grinding might present its own issues (assuming you have a toolpost grinder), because the jaws will not be under the same tension while grinding as they would be in use. You could make a ring and tighten the jaws internally on it, but, depending on how much play there is, the back of the jaws will want to kick outwards and the result after grinding might be worse that when you started.

    I think the best way would be to set them up on an angle plate on a surface grinder and indicate the clamping surface of the jaws to compensate for the taper. Because it's a 4-jaw, you don't need to worry about them all being matched to a scroll as you would with a 3-jaw so a bit of variation in the final length doesn't matter so much.

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    Hi Phil, Guys,

    Yes I agree ! Clamping them to a reference surface and grinding them square might be the best way. That is of course assuming that the guides are not badly worn as well leaving the jaws loose in them.
    Best Regards:
    Baron J.

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    Quote Originally Posted by caskwarrior View Post
    I would not consider that acceptable. You could grind them in place with a toolpost grinder, or take them and get them gang ground.
    I don't as yet have a tool post grinder, and lack the skill to do this job I think.
    What exactly is Gang Ground?

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    Quote Originally Posted by elanjacobs View Post
    Definitely shouldn't be out that much, you'd be losing a lot of clamping force with only point contact..

    I wonder if toolpost grinding might present its own issues (assuming you have a toolpost grinder), because the jaws will not be under the same tension while grinding as they would be in use. You could make a ring and tighten the jaws internally on it, but, depending on how much play there is, the back of the jaws will want to kick outwards and the result after grinding might be worse that when you started.

    I think the best way would be to set them up on an angle plate on a surface grinder and indicate the clamping surface of the jaws to compensate for the taper. Because it's a 4-jaw, you don't need to worry about them all being matched to a scroll as you would with a 3-jaw so a bit of variation in the final length doesn't matter so much.
    Yep, they are digging in at the rear, and the outer end of a bar has movement, not insignificant either.
    I will take the jaws out and see if my small try square shows where the problem lies.
    They are not ground flat either,...a photo tomorrow is in order.

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    Quote Originally Posted by BaronJ View Post
    Hi Phil, Guys,

    Yes I agree ! Clamping them to a reference surface and grinding them square might be the best way. That is of course assuming that the guides are not badly worn as well leaving the jaws loose in them.
    There is no wear as it is a new chuck John.

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    Hi Phill,

    A new chuck ! Is it time to return it as defective ? Or did you mean S/H but new to you ?
    Best Regards:
    Baron J.

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    Do you know what brand it is? If it's brand new, returning it would be the order of the day, as it would be unacceptable to use.
    Kryn
    To grow old is mandatory, growing up is optional.

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    Quote Originally Posted by BaronJ View Post
    Hi Phill,

    A new chuck ! Is it time to return it as defective ? Or did you mean S/H but new to you ?

    Brand new John. Or at least it was when I bought it in December last year

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    Quote Originally Posted by KBs PensNmore View Post
    Do you know what brand it is? If it's brand new, returning it would be the order of the day, as it would be unacceptable to use.
    Kryn
    Chinese unit from a machinery supplier in Perth.

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    What is it like when you have a job set up?
    I don't really understand what your concern is, as you would never have the jaws that close.
    Set a job up and check the runout and clearances then.

  13. #13
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    There is another thing which can cause this. I imagine it is rare, but it does happen, so it might be worth checking if you decide to grind the jaws instead of returning the chuck. The chuck in question was very cheap at a closing down sale. It was roughly hand stamped CENTRAL - no other markings or indication of country of origin. The jaw slides were not machined parallel to the face of the chuck so the gripping faces of the jaws were not parallel to the lathe's axis!

    by the time I had worked out what the problem was the closing down sale had finished, so it could not be returned. I did grind the jaws in place so their faces were parallel to the lathe's axis, but didn't even try to grind the outside steps on the jaws for holding large diameter material, so it is useless as a lathe chuck. It still sees very limited use on the rotary table.

    Frank.

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    Quote Originally Posted by pipeclay View Post
    What is it like when you have a job set up?
    I don't really understand what your concern is, as you would never have the jaws that close.
    Set a job up and check the runout and clearances then.
    Maybe I wasn't clear. Mount a bar in the chuck firmly, and only the very inner part of the jaws make contact, so the outer end of the bar can move in every direction.

  15. #15
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    Quote Originally Posted by franco View Post
    There is another thing which can cause this. I imagine it is rare, but it does happen, so it might be worth checking if you decide to grind the jaws instead of returning the chuck. The chuck in question was very cheap at a closing down sale. It was roughly hand stamped CENTRAL - no other markings or indication of country of origin. The jaw slides were not machined parallel to the face of the chuck so the gripping faces of the jaws were not parallel to the lathe's axis!

    by the time I had worked out what the problem was the closing down sale had finished, so it could not be returned. I did grind the jaws in place so their faces were parallel to the lathe's axis, but didn't even try to grind the outside steps on the jaws for holding large diameter material, so it is useless as a lathe chuck. It still sees very limited use on the rotary table.

    Frank.
    That is a very strong possibility Frank. I'll try to confirm that tomorrow.
    Thanks Frank.

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