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Chuck Runout Repair?

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  • Chuck Runout Repair?

    I have a 6", four jaw self centering chuck. It's always been a PIA, and now I know why. Threw a dial indicator on it (outside chuck body) and it has about 11 thou runout from 0 degrees to 180 degrees. Then put a test bar in the chuck. Same runout, same spots. OK I said. Loosen the backplate bolts and tap it back in place. NOT. Wouldn't move at all.

    Took it apart, and the backplate has an internal flange that slips into the chuck body (not quite interference, but it is dead nuts on). Tried rotating the chuck on the backplate a couple of times but no dice. So, the only way I see to fix this is to take a gnat's arse off the flange so the body can move a bit on the backplate. Question is: will the bolts (six of them) hold the chuck true without any help from the flange? If push comes to shove, can I ream the backplate holes slightly if I can't get enough by making the flange diameter a little smaller?

    I indicated the bare spindle too. It is all but perfect, so I know the issue is in the chuck.

    Mark

  • #2
    I think that pushing the chuck that far off center and having the bolts pull at an angle, you may find it wants to move right back where it was. I would ream the holes a few thou. larger depending on the original size. You could also just drill and tap some new holes in the back plate or even try another back plate. I would love to know where the error really lies. Who is the chuck made by???

    JL.................

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    • #3
      Go for it! What have you got to lose? The back plate on my three jaw looks like a war zone, lotsa extra holes. And the four jaw, I bought new and had to drill my own set. Wasn't very happy with the results, so ended up reducing the flange and ratting out the holes until I WAS happy with the results. Well, as happy as you can be with a screw on chuck, they screw up a little different each time. But that's a whole nudder issue, now idn't it. I haven't had a crash bad enough to shift anything, knock on wood.
      I'm here hoping to advancify my smartitude.

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      • #4
        I honestly think that if I remove a bit of the flange there will be enough "wobble" room in the bolt holes to get a few thou. I assume the flange was built in as structural to keep the chuck where it is. It just leaves no room to tweak.

        I'll take about .010 off the flange and see if it'll come back in. If not I'll ream the holes to suit. And you are right, I have nothing much to lose. It's a POS now. Can't make it much worse.

        I wish I had a good three jaw SC to replace this heavy old four. I rarely use it (for obvious reasons). It's almost as easy to just dial in the four jaw indy chuck. Just not as fast.

        Comment


        • #5
          It's been done successfully before. People have made a sort-of Adjust-True chuck for themselves that way. The bolts will indeed keep it from moving after you adjust it.
          Last edited by SGW; 04-17-2012, 10:33 AM.
          ----------
          Try to make a living, not a killing. -- Utah Phillips
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          • #6
            How thick is the back plate? If there's plenty of meat you could just machine the register right off and cut a new one.

            Quite a few people have advocated having the register a bit undersize so you can centre work by tapping the chuck. A poor mans' GripTru if you like.
            Paul Compton
            www.morini-mania.co.uk
            http://www.youtube.com/user/EVguru

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            • #7
              If your back plate is thick enough, you can face the register (or flange) completely off and cut a new one. I had the same issue with a Polish 3-jaw I aquired in a trade; runout was about .012". With a new register cut it is <.002"

              The bolt holes in the back plate should be larger than the bolts to prevent the bolts from drawing the chuck off center. The register aligns the chuck on the back plate.

              Tom
              Tom - Spotsylvania, VA

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              • #8
                Chuck

                I would turn down the register on the backplate as stated above, and if you have room make it a little farther back to allow room to drill and tap for setscrews behind each chuck jaw. The setscrews would then bear on the turned down part of the register. Then you would have a real "Adjust Tru" chuck and the setscrews could help hold it in position. However, a lot of chucks work just fine without the setscrews.

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                • #9
                  Originally posted by Toolguy
                  I would turn down the register on the backplate as stated above, and if you have room make it a little farther back to allow room to drill and tap for setscrews behind each chuck jaw. The setscrews would then bear on the turned down part of the register. Then you would have a real "Adjust Tru" chuck and the setscrews could help hold it in position. However, a lot of chucks work just fine without the setscrews.

                  The set screws are definitely needed.

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                  • #10
                    I have to disagree, the set screws are not needed. He has six bolts clamping the chuck to the back plate, it's going nowhere. 3 would be enough.

                    When was the last time your compound/top-slide swiveled/slipped under load, with only two bolts clamping it to the carriage?

                    Phil

                    Originally posted by moe1942
                    The set screws are definitely needed.

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                    • #11
                      The set screws are not needed, but they make adjusting easier and help to maintain the setting during tightening of the hold down screws.

                      JL...................

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