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Dialing in a 3 Jaw Chuck

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  • #46
    Originally posted by wierdscience View Post
    Buy a new Bison, use the master pinion only, (they are marked with a -0- next to them or a ')forget the other two exist, throw the old chuck away.

    Or, buy a REAL chuck.

    The "real" chucks have just one pinion, so there is no question which is the master. They are better made, and do not need many pinions in order to tighten decently.
    CNC machines only go through the motions.

    Ideas expressed may be mine, or from anyone else in the universe.
    Not responsible for clerical errors. Or those made by lay people either.
    Number formats and units may be chosen at random depending on what day it is.
    I reserve the right to use a number system with any integer base without prior notice.
    Generalizations are understood to be "often" true, but not true in every case.

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    • #47
      Originally posted by mattthemuppet View Post
      I tried the "tap tru" method of dialing in a 3 jaw with an old but decent 4" Bison. Not very impressed. It's really hard to knock it in one direction without messing up its position in a different direction (imagine truing up someting on a faceplate with a mallet) and it can get knocked out of alignment if you have a jam. Next backplate I make will be the usual "hair less than the chuck back ID" method and I'll use the 4 jaw if I need to be fussy or rechuck a piece.
      Sorry to hear about your inability to master the tapping method, I use six screws per chuck and the art is in the slackening enough for gentle tapping to move things, but not too slack to change when the screws are tightened. I would adjust the body of the chuck to run true before thinking of grinding the jaws, those chucks having been ground seem to stay true without any more adjustment.

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      • #48
        Originally posted by J Tiers View Post

        Or, buy a REAL chuck.

        The "real" chucks have just one pinion, so there is no question which is the master. They are better made, and do not need many pinions in order to tighten decently.
        Bison chucks are REAL, but they still have three pinions-

        I just need one more tool,just one!

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        • #49
          I have seen 6 jaw chucks with only one pinio, and 4 jaw, but not a three jaw. The extra pinions come in handy for undoing the chuck.

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          • #50
            Originally posted by old mart View Post

            Sorry to hear about your inability to master the tapping method, I use six screws per chuck and the art is in the slackening enough for gentle tapping to move things, but not too slack to change when the screws are tightened. I would adjust the body of the chuck to run true before thinking of grinding the jaws, those chucks having been ground seem to stay true without any more adjustment.
            inability to master a skill is one way of looking at it I suppose. Maybe next time I read of you struggling with something I'll apply the same.

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            • #51
              That won't be long for you to wait.

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              • #52
                Originally posted by old mart View Post
                I have seen 6 jaw chucks with only one pinio, and 4 jaw, but not a three jaw. The extra pinions come in handy for undoing the chuck.
                I have maybe four 3 jaw chucks, and I do not think any of them have more than one pinion. It's all that is needed. Made by Buck, and other good makers, so no, not cheapo chucks. It's the cheapos that seem to have three.
                CNC machines only go through the motions.

                Ideas expressed may be mine, or from anyone else in the universe.
                Not responsible for clerical errors. Or those made by lay people either.
                Number formats and units may be chosen at random depending on what day it is.
                I reserve the right to use a number system with any integer base without prior notice.
                Generalizations are understood to be "often" true, but not true in every case.

                Comment


                • #53
                  El cheapo:

                  Click image for larger version

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                  inb4 I get ribbed over chatter.
                  21" Royersford Excelsior CamelBack Drillpress Restoration
                  1943 Sidney 16x54 Lathe Restoration

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                  • #54
                    I think all of mine have more than one pinion... and they are sure not cheapo...

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                    • #55
                      Three pinions are not the exclusive property of cheapo chucks, but the cheapos seem always to have them. And so you have "better" and "worse" pinions as far as off-center is concerned.

                      Not a problem with the chucks having one...... Have just one and have it work right! 😁
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

                      Comment


                      • #56
                        Originally posted by Willy View Post
                        What's everybody's favorite method of eeking out those last few thou of runout when using a three jaw chuck?
                        Yes I know, that's what a four jaw chuck is for but sometimes when in a hurry and absolute precision isn't required (but always welcome ), what are some of the techniques you use in order to dial out an extra 2 or 3 thou less radial runout?
                        I modified my chuck backing plate so I could move the chuck around more, I also enlarged the through holes for the screws so there would be more room to move them about. Then I simply loosen the screws a little and tap it in. This bellmouthed old worn chuck still manages to keep it within a few hundreths after that.

                        Edit: It's a single pinion chuck, I often find it annoying when I want to open the chuck jaws.
                        Last edited by DennisCA; 12-22-2020, 02:57 AM.

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                        • #57
                          Dennis, could you show Mattthemuppet exactly how you do it?

                          Going back to the 12" chuck of TMB, I worry about the thickness of that backplate. The three SHCS that hold it on are 16mm according to the Bison website, and when threaded into cast iron which is 3/4" thick means that less than 1.2 diameters of thread in theory are holding it on. I would be happy with 2 diameters which is 32mm, over 1.25". That thickness of backplate would be much stiffer.
                          Last edited by old mart; 12-22-2020, 01:41 PM.

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                          • #58
                            old mart, you seem to think I'm some kind of ignoramus or something. It's not a difficult concept to get, it just doesn't work well in my case. I even tried the outside jaws, using a gage pin as reference, without luck this morning. I'm in the middle of taking apart and cleaning the chuck, just in case that's causing the problem. Maybe it's the terrible 3 backplate screws, instead of the fabled 6 that seem to make the difference. Whatever it is, it's a royal pain in the ar$e to true up and doesn't stay true forever even if I do get it close. Clearly others have had great success with this technique, I haven't. Clearly others are happy prosetylising this technique, I am not. The next 3 jaw backplate I make (probably for this chuck) will use the normal "just barely taps on" fit for the locating boss.

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                            • #59
                              MM if you have a mill and RT, I recommend adding the extra holes, for security. While the chuck is being cleaned, you could take a tiny skim of the backplate and also fix the "terrible screws". If you have rear mounts, perhaps spring washers would help. I have never tried the tapping method with a chuck bigger than 160mm, the weight goes up rapidly with size and may be the problem. I keep a mallet with the lathe with copper one end and nylon the other for tapping things.

                              It's a shame that TMB's chuck cannot have any extra fixings added owing to the design.

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                              • #60
                                Originally posted by old mart View Post
                                MM if you have a mill and RT, I recommend adding the extra holes, for security. While the chuck is being cleaned, you could take a tiny skim of the backplate and also fix the "terrible screws". If you have rear mounts, perhaps spring washers would help. I have never tried the tapping method with a chuck bigger than 160mm, the weight goes up rapidly with size and may be the problem. I keep a mallet with the lathe with copper one end and nylon the other for tapping things.

                                It's a shame that TMB's chuck cannot have any extra fixings added owing to the design.
                                It might be able to yet. I haven't explored bolts tapped into the chuck going from the back. It won't go all the way through, so I dunno if it will do any good. But I've got another thread for that, I don't need to clog this one. Certainly a disadvantage of 3 pinion set-tru chucks.


                                ​​​​​​Matt, some hysteresis from dirt may be messing with you. Or tightening the bolts may be moving it. A good clean might help, might not.
                                21" Royersford Excelsior CamelBack Drillpress Restoration
                                1943 Sidney 16x54 Lathe Restoration

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