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Grinding jaws on 4 jaw chuck?

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  • Grinding jaws on 4 jaw chuck?

    Guys...I've been reading about this chuck jaw grinding.
    So far all I've found is info on trueing up 3 jaw chucks.
    I want to use Harlod V's method...clamp down on a washer that's set in the very back of the jaws....the grind off the little bit that's left after its all done.
    But...trying to get all the jaws lined up perfectly with a small washer deep in the chuck...would take awhile.
    So I'm wondering...what would be wrong...with using the washer but offsetting one jaw at a time?
    That way you'd still have the pressure on the jaw....but you'd only grind one at a time?
    Am I missing something?
    Thanks!
    Russ
    I have tools I don't even know I own...

  • #2
    Why?

    Perhaps my inexperience is showing... since you can dial in a workpiece to have zero runout what purpose would grinding the jaws serve?

    Comment


    • #3
      Three of the jaws are belled outwards...while one is belled or tapered inwards....it holds stock at a cocked over angle.
      No big deal for long stuff with steady rest or center support....just try setting up a short piece...
      I have tools I don't even know I own...

      Comment


      • #4
        Russ, instead of messing around with grinding in situ, why not take them out and clean them up with a cut on the mill?
        As it's an independent 4-jaw they don't need to be setup to close concentric like a 3-jaw.

        Peter

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        • #5
          On a three jaw, my best idea I have heard is to make a large ring that encircles the jaws, with cutouts for the jaw to fit into, hollow in the center. Contact each jaw on the angled surfaces either side of the gripping surface. The cutout can be a large hole with the inner surface cut to fit the jaw angle.

          This leaves the gripping surface of the jaw exposed, and you can tighten the jaw so it has similar pressure to what it sees when actually gripping a piece.

          Then grind as usual.

          The other method, one I used once, was to put a large washer ALL the way back, behind the gripping surface, so that it was touching the thread portion of the jaw. This left the gripping surface free to be ground, the hole in the washer let the shaft of the grinder room to pass the end of the jaw.

          Both of these methods were advised for 3-jaw chucks, don't see why they wouldn't work for 4-jaw ones.

          Steve

          Comment


          • #6
            Peter...hmmm..I'll have to check that out.
            If you used a key in the slot that rested on the top of the vise...they should all turn out identical.
            I have tools I don't even know I own...

            Comment


            • #7
              I had a well worn 4 jaw on my old South Bend that would cock things when you grabbed them. I tried trueing them up on the mill and it helped some, but because the wear/spring in the chuck body was not equal it still cocked the workpiece a little. I ended up grinding them in place on the lathe with a die grinder mounted as a ghetto tool post grinder (hose clamps to a piece of plate that was bolted into the compound. That actually got it pretty true except at the ends of the range where one jaw was sprung in the body from a PO crash.

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              • #8
                Can you reverse them? If so, that would be the easy way to cut them parallel to the spindle. Grinding shouldn't be required unless something horrible happened and you have hardened jaws that are bell-mouthed. If so, then !

                Comment


                • #9
                  I'm not too worried about the chuck body itself.
                  The jaws are still very tight in the slots. I indicated the slots last night and they are all bang on.
                  It's the jaws that are weird...doesn't look like they are very hard...and they are showing some uneven wear patterns along the grip length.
                  I have tools I don't even know I own...

                  Comment


                  • #10
                    Torker. If your 4 jaw work has an uncorrectable wobble you may be swallowing the work. The jaws are never perfect. Instead of grinding the jaws grip no more than 1/2" of the end. For long work where you have to run the excess back into the spindle, wrap a single turn of heavy gage steel or copper wire around the work and grab the wire in a jaw serration.

                    Since this results in a less secure grip you're going to have to use centers and steady rests more often.

                    You may have to grind a wire serration if your jaws are smooth. Measure back about 1/4 and grind a 3/32" wide x 1/16" deep serration in place (use the washer trick) with a mounted wheel dressed like an Acme tool (mounted wheel style A -37). This is a good job for a Dremel or a die grinder. A wire serration has no effect on the chuck's usability and ensures the wire padding lies in a true radial plane.

                    Comment


                    • #11
                      Originally posted by 2ManyHobbies
                      Can you reverse them? If so, that would be the easy way to cut them parallel to the spindle. Grinding shouldn't be required unless something horrible happened and you have hardened jaws that are bell-mouthed. If so, then !
                      No..I couldn't do that...why that would be too easy. Geez...that would be just stupid simple wouldn't it? Thanks!
                      Think outside the box....think outside the box..
                      I have tools I don't even know I own...

                      Comment


                      • #12
                        Hang on..if you reverse the jaws..the newly ground jaw faces would be rounded.
                        I'm bettin that wouldn't be good.
                        I have tools I don't even know I own...

                        Comment


                        • #13
                          Russ,
                          if you reverse the jaws and machine them the "gripping" surface will be convex instead of flat or concave. may not matter...

                          - Scott

                          Comment


                          • #14
                            I bought a 4 jaw from KBC and it had the same problem right out of the box. I bought it about a year before I took it out of the box so sending it back was no longer an option. I set it up on the vertical mill with the face of the chuck facing up and ground each jaw with a 2 inch stone.Only had to grind a few thou off each jaw. Worked perfect.

                            Comment


                            • #15
                              I'm ill at ease with the idea of grinding chuck jaws using a washer close to the inside edge. The center of force may not be the same as when something is gripped near the outer ends.

                              For establishing conditions similar to real use before grinding for squareness, I still think the ring at the front is the best answer. I've seen the idea of drilling a circle of holes in a plate for the jaws, then cutting out a center circle intersecting these to allow access for the grinding. A four jaw should be even easier since you only need two jaws at a time. On a small chuck of mine, I used a carbide drill to put holes in the tops of the jaws so I could use dowels or roll pins to grip a ring to spread the jaws before grinding.
                              .
                              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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