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    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
    Hello and welcome to the forum.

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

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    • #3
      Thnx

      Sent from my SM-N920V using Tapatalk

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      • #4
        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.

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        • #5
          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

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          • #6
            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.

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            • #7
              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, 11:05 AM.
              Green Bay, WI

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              • #8
                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

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                • #9
                  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...

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                  • #10
                    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, 06:02 AM.
                    Location: Helsinki, Finland, Europe

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                    • #11
                      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.

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                      • #12
                        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.
                        Chilliwack BC, Canada

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                        • #13
                          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
                          Tom - Spotsylvania, VA

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                          • #14
                            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.
                            Lynn (Huntsville, AL)

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                            • #15
                              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!

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