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Thread: Help needed

  1. #11
    Join Date
    Jan 2003
    Location
    Atascosa County, Texas
    Posts
    8,175

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    Welcome to the forum!

    If your chuck is out .010", you may want to remove, disassemble and clean it before attempting to grind. You could have chips and dried grease hindering jaw movement and/or seating against the scroll. It's important to keep the jaws preloaded against the scroll, to remove lash, during the grinding process. I prefer to use a ring or washer clamped in the jaws instead of drilling holes in my jaws. Either way, the setup needs to be precision so no single jaw is more loose than the others. One of my chucks has reversible jaws so I made extended bolts to use while grinding. I use the extensions to hold a precision washer/ring.

  2. #12
    Join Date
    Dec 2015
    Location
    Chilliwack, BC, Canada
    Posts
    5,581

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    Another reason for jaw runout is the type of wear called "bell mouthing". That's when we've used it enough on the very tips to wear down the tips of the jaws more than the rear/inner parts. Also the jaws running in the slots wear a little over time. Both of these things cause a little bell mouthing.

    The 6 jaw chucks are supposed to be better for holding round items though. So I find it odd that you've got more than .010" of runout. I strongly suspect it's due to something the others mentioned already.

    And keep in mind that 6 jaw chucks are intended to be used with turned items for second operations. Or holding tubing and pipe that will try to squeeze down to a tri-lobed shape when held by a 3 jaw. They do OK at holding rough stock but given the tolerances for rough stock all 6 jaws may not be holding evenly. And with solid stock a few may not be touching at all. Holding rough stock is were a regular 3 jaw shines.

  3. #13
    Join Date
    Apr 2010
    Location
    Spotsylvania, VA
    Posts
    475

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    It would probably be best to determine the cause of the runout before taking any action. I acquired a nearly new Polish-made chuck that had terrible runout. After some experimenting, I determined the cause of the runout was that the chuck was not centered on the back plate. A hack job from the previous owner, I assume. I removed the chuck from the back plate, faced it square and recut the index for the chuck for a snug fit. It made a world of a difference.

    Tom

  4. #14
    Join Date
    Jan 2002
    Location
    Huntsville Ala
    Posts
    5,880

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    Quote Originally Posted by BCRider View Post
    Another reason for jaw runout is the type of wear called "bell mouthing". That's when we've used it enough on the very tips to wear down the tips of the jaws more than the rear/inner parts. Also the jaws running in the slots wear a little over time. Both of these things cause a little bell mouthing.

    The 6 jaw chucks are supposed to be better for holding round items though. So I find it odd that you've got more than .010" of runout. I strongly suspect it's due to something the others mentioned already.

    And keep in mind that 6 jaw chucks are intended to be used with turned items for second operations. Or holding tubing and pipe that will try to squeeze down to a tri-lobed shape when held by a 3 jaw. They do OK at holding rough stock but given the tolerances for rough stock all 6 jaws may not be holding evenly. And with solid stock a few may not be touching at all. Holding rough stock is were a regular 3 jaw shines.
    BCRider, He didn't say it's a 6 jaw chuck. He said it's a 6 inch, 3 jaw chuck.

  5. #15
    Join Date
    Jan 2003
    Location
    On the Oil Coast,USA
    Posts
    19,634

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    Hold on,before we jump into grinding jaws,let's see if the chuck is marked for a master pinion.The three pinions used to tighten the chuck,look and see if one of them has a mark on the chuck body next to it.If it does,tighten the chuck with that pinion only and then check your run out.

    If it doesn't have a mark,use one to tighten the chuck,mark it with a marks-o-lot,then check run out and record your reading.Then repeat for the other two pinions.Odds are one pinion will give you better run out than the other two.If that is the case,then that pinion is the master.Mark it by stamping a letter or number,or if nothing else a couple good center punch marks in the chuck body next to it.

    At the factory and in the shop when the jaw faces are ground as the final operation in truing the jaws.A lashing ring is used like mentioned before to remove excess lash before grinding.The pinion used to tighten the chuck on that lashing ring is the one that will yield good run out,the other two not so much.
    I just need one more tool,just one!

  6. #16
    Join Date
    Oct 2002
    Location
    Saskatoon, Saskatchewan
    Posts
    3,100

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    Quote Originally Posted by flathead4 View Post
    It would probably be best to determine the cause of the runout before taking any action. I acquired a nearly new Polish-made chuck that had terrible runout. After some experimenting, I determined the cause of the runout was that the chuck was not centered on the back plate. A hack job from the previous owner, I assume. I removed the chuck from the back plate, faced it square and recut the index for the chuck for a snug fit. It made a world of a difference.

    Tom
    It would probably be best to determine the cause of the runout before taking any action.
    ^This!^ As many others have pointed out, there can be more than one reason for runout to happen and a methodical approach is needed to ensure that you find and correct the base problem...not just mask it.

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