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Thread: Help needed

  1. #1
    Join Date
    Aug 2019
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    3

    Default Help needed

    Hello, new here. How does one true up the jaws on a 6 inch 3- jaw chuck, they on a clausing 12 x 36 lathe variable speed. They do un-bolt from chuck & can be turned around for OD clamping.
    Alan
    PS: I'm self taught very little schooling but had good mentors over the years.

    Sent from my SM-N920V using Tapatalk

  2. #2
    Join Date
    Jan 2008
    Location
    Traverse City, MI
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    1,608

    Default

    Hello and welcome to the forum.

    I've moved this post to the General forum, as it will get more notice here.
    George

  3. #3
    Join Date
    Aug 2019
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    3

    Default

    Thnx

    Sent from my SM-N920V using Tapatalk

  4. #4
    Join Date
    Mar 2015
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    3,933

    Default

    You would pre-tension them and take a tool post mounted grinder and true them up. I'd say if they are withing .003 repeatability, I wouldn't bother. Because you have two piece jaws, if you want truly accurate work holding for a specific diameter, you can use soft jaws that bolt in where the hard jaws normally would go. Go on Youtube, there are many videos describing both techniques better than I can in a post.

  5. #5
    Join Date
    Jul 2007
    Location
    West Michigan
    Posts
    3,020

    Default

    Also make sure the jaws are in the right position. Most chucks have numbers that correspond to the numbers on the jaws.

    Brian
    OPEN EYES, OPEN EARS, OPEN MIND

    THINK HARDER

    BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

    MY NAME IS BRIAN AND I AM A TOOLOHOLIC

  6. #6
    Join Date
    May 2007
    Location
    Live Oak, TEXAS
    Posts
    1,835

    Default

    I wouldn't bother truing them up, unless you're getting ALOT of runout, like more than .010"
    Reversible jaws on a 3-jaw chuck are notorious for having some runout on them.
    For dead-nuts accuracy, you'll need a 4-jaw chuck.

  7. #7
    Join Date
    Jul 2001
    Location
    Green Bay, WI
    Posts
    3,588

    Default

    Nothing worse than a bad chuck.
    You don't have to be fancy when grinding the jaws
    First, Protect your ways. and place some scotch tape inside where the master jaws engage the scroll, to prevent grit from entering the scroll through centrifugal force.
    Take your chuck jaws and drill a 1/8 " hole in the front of them, about 3/8" deep.
    Clamp on a ring at the front (!) of your jaws to preload ( Compression , not tension !)
    jury rig a grinder if you don't have a ID Grinder.
    I use a chain saw sharpener (25K RPM) mounted to a Aloris post. Simple but very effective.
    The pins on the front of the chuck are 1/8 dowels, and the holes are drilled with a 1/8 masonary bit (with water cooling) and exact hole location is un-necessary, as the ring loads the jaws irrespective of location.
    The holes do NOT have to be precisely located, they just need to load the ring and do not affect your chuck operations.
    Mark the inside contact point of each jaw with a felt tip marker.
    As you grind, you will see the contact point move outward as the ink is ground off. as soon as all ink is gone, spark out , and quit.

    I like to cover my ways with plastic sheet , and then lay a wet paper towel on it to absorb all grit. when done, wipe everything down , and roll up the plastic and toss
    BEFORE you start, you need to select ONE wrench socket and mark it ! Use Paint that will stay on
    I like to use the one near the Logo. This is the socket to use for tightening on your ring, and it becomes "The Master Socket"
    After revising the jaws, and mounting work, the master socket will always give you the most accurate concentricity because the scroll was shifted from that point during the grinding process !
    Rich
    Go here to see some pictures in post 9
    http://www.chaski.org/homemachinist/...k+jaws#p173678
    Last edited by Rich Carlstedt; 09-06-2019 at 11:05 AM.

  8. #8
    Join Date
    Aug 2019
    Posts
    3

    Default

    Thnx everyone for the helpful replies. I do have more than 0.010 run out, this is why I'm asking. I'm a where of a 4-jaw chuck & a collet chuck..i have both. I also have digital readout.
    As I have a manual vertical mill with readouts as well.
    But everything self taught from mentors that are gone : (
    Al

    Sent from my SM-N920V using Tapatalk

  9. #9
    Join Date
    Dec 2002
    Location
    Friesland, Netherlands
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    2,290

    Default

    Just how much runout do you have? If it's *lots*, then I think Brian might have it - either a jaw in the wrong slot, or a jaw inserted one revolution of the scroll too late.

    Take them all out, turn the scroll with the key until you just see the leading edge. Insert jaw 1 in slot 1, turn the scroll until you see the leading edge and insert jaw 2 etc.

    Does that fix it?

    Ian
    All of the gear, no idea...

  10. #10
    Join Date
    Dec 2016
    Location
    Helsinki, Finland, Europe
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    3,619

    Default

    Rich Carlstedt gave already good description of the job. I'd add that clean, clean and clean all the mating surfaces from chips and burrs. And make double-sure that jaws are in proper order.
    "Non-ideal" situation to grind the chuck jaws only to find out that you had chip stuck on the chuck mounting surfaces or jaws in wrong order ...

    edit: I have used plasticine/play-doh* to seal the gaps between jaws and chuck body to keep the grit away.

    *) brand name "play-doh" is too crumbly, I'm guessing the non-drying dinosaur oil version would be called plasticine?
    Last edited by MattiJ; 09-11-2019 at 06:02 AM.

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