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Novel way to center work in a 4jaw chuck.

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  • #16
    Originally posted by rbertalotto View Post
    I just use a 4 jaw "Tru-Adjust" chuck. Loosen four bolts on back plate, they are kept snug with Belview washers. Tap chuck with a small lead hammer using a dial indicator on the work piece......done!
    If it is a 4 jaw, why are you tapping it true ? ? ?

    -D
    DZER

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    • #17
      Hopefully you don't run very high rpm. Bye-bye balance if you're moving the whole chuck all over the place on the backing plate with irregular workpieces. I'm in the just use the 4-jaw camp. It takes me about 1 minute to get a part centered close enough (.010"-.020") to get the indicator in play, and about another 2 revolutions of the chuck to get within a thou or so. For initial setting I just set the part between two jaws and touch the jaws to it, then eyeball the jaws to the concentric lines on the face of the chuck. I can generally get closer than .020" that way real quick. I could see that tailstock method being somewhat useful for someone who has problems getting a 4-jaw set up.

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      • #18
        I only use my 4 jaw for irregularly shaped pieces, so the original poster's idea doesn't work for me. I have gotten better at centering stuff in the 4 jaw, but it still isn't a quick process for me. I seem to spend an inordinate amount of time tightening a little bit on this jaw, loosening a bit on that jaw. I use a 16" piece of 1/4" diameter cold rolled steel rod with a point on one end and the other end held in my tailstock chuck. I have a dial indicator with an oversize "shoe" on the end of it. The pointed end of the rod fits into a center-punch mark on whatever I am holding, and the oversize "shoe" rides against the side of the 1/4" rod about 2" out from the face of the chuck. This certainly works well for me, but I wish I was a bit faster at doing it. -----Brian
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #19
          Originally posted by Doozer View Post

          If it is a 4 jaw, why are you tapping it true ? ? ?

          -D
          May be a 4 jaw scroll chuck.
          A set true independent jaw chuck would be silly at best.

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          • #20
            Maybe I'm a porn star.

            -D
            DZER

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            • #21
              I have left my four jaw chuck in one of my lathes for a while now. I put it on there to do some sort of fussy work on something and decided to just leave it in the force myself to practice dialing stuff in. I must say that with a dedicated indicator, two chuck keys, and a bit of practice it really does not take long to dial something in pretty well. Just a minute or two most of the time.

              Very little that I do is super critical, but it just feels like a good skill to work on and is handy for the times that you do need to get something closer than three jaw true.

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              • #22
                I have always avoided a four jaw scroll chuck, they rely on being perfect and also the work being dead cylindrical. Even square stock would have to be perfectly square.

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                • #23
                  Originally posted by alanganes View Post
                  I have left my four jaw chuck in one of my lathes for a while now. I put it on there to do some sort of fussy work on something and decided to just leave it in the force myself to practice dialing stuff in. I must say that with a dedicated indicator, two chuck keys, and a bit of practice it really does not take long to dial something in pretty well. Just a minute or two most of the time.
                  I do the same unless I switch over to collets. The 3 jaw I have has worn jaws so I only use it for 1 off jobs and soft jaws.

                  I only use one key but have a dedicated indicator for the qctp and like you said a minute or 2 tops is better than what a 3 jaw will get.

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                  • #24
                    The same retired navy engine man, that used the threaded rounds in the tail stock for setting up work in a 4 jaw chuck, gave me a stainless steel pocket ruler in 1/64ths. He had cut it off to three inches in length, and ground off the back side to give it the form of a thin L shaped ruler. I have used this to set 4 jaw chucks for a lot of years, that is when I can find it.

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                    • #25
                      A hook rule ? ? ?
                      DZER

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                      • #26
                        Yes, a hook ruler, I couldn't think of the name when I did my last post. With the modified hook ruler, and a sharp dead center in the tail stock. I set two adjoining jaws as close to dead on to the radius measurement of the part as my tired eyes allow. Then lightly snug up the other two jaws usually with in .025". Then use two keys for final adjustment, that is if I can find both keys.

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                        • #27
                          JC Hannum (RIP) described a method years ago that works great:

                          Center by eye first, then put your indicator against the part. Rotate by hand, noting "high" and "low" readings. Rotate so the reading is halfway between the 2, then zero the indicator. Rotate the part until a jaw is lined up with the indicator plunger. Adjust that jaw and the one opposite until indicator reads Zero. Rotate 1/4 turn until another jaw is under the indicator plunger, adjust that jaw and the one opposite until indicator reads Zero. Rotate chuck one turn to verify centering, you should be very close, if not right on.

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                          • #28
                            Originally posted by rogee07 View Post
                            Yes, a hook ruler, I couldn't think of the name when I did my last post. With the modified hook ruler, and a sharp dead center in the tail stock. I set two adjoining jaws as close to dead on to the radius measurement of the part as my tired eyes allow. Then lightly snug up the other two jaws usually with in .025". Then use two keys for final adjustment, that is if I can find both keys.
                            I like the hook rule idea. Not sure why that never occurred to me. Sounds like another small tool to just leave by the lathe along with the two chuck keys and the dedicated indicator.

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                            • #29
                              Originally posted by jdunmyer View Post
                              JC Hannum (RIP) described a method years ago that works great:

                              Center by eye first, then put your indicator against the part. Rotate by hand, noting "high" and "low" readings. Rotate so the reading is halfway between the 2, then zero the indicator. Rotate the part until a jaw is lined up with the indicator plunger. Adjust that jaw and the one opposite until indicator reads Zero. Rotate 1/4 turn until another jaw is under the indicator plunger, adjust that jaw and the one opposite until indicator reads Zero. Rotate chuck one turn to verify centering, you should be very close, if not right on.
                              That's the way I've always done it.

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                              • #30
                                Originally posted by jdunmyer View Post
                                JC Hannum (RIP) described a method years ago that works great:

                                Center by eye first, then put your indicator against the part. Rotate by hand, noting "high" and "low" readings. Rotate so the reading is halfway between the 2, then zero the indicator. Rotate the part until a jaw is lined up with the indicator plunger. Adjust that jaw and the one opposite until indicator reads Zero. Rotate 1/4 turn until another jaw is under the indicator plunger, adjust that jaw and the one opposite until indicator reads Zero. Rotate chuck one turn to verify centering, you should be very close, if not right on.
                                Yup. That is the fastest and easiest way.

                                Get high and get low, split the difference, then you have your number.
                                Go 90° and hit that same number, spin a final time, verify and tweak.

                                So much belly ache on centering a 4 jaw.
                                Am I the only one who sees cause and effect relationships
                                and solves problems based on the physical world ? ?

                                -D
                                Last edited by Doozer; 01-22-2021, 09:08 AM.
                                DZER

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