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  • Adjust true Chuck questions.

    Several years ago, I bought a Bison 6 jaw adjusts true chuck and D1-3 back plate. When I got it, I put it together stuck a piece of drill rod in it and proceeded to zero with a DTI. Over time it was on and off the machine numerous times and everything worked fine. Recently when it was reinstalled things took a bad turn. I probably did not get it back in the same rotational position. When I tried to dial it in it would not adjust very much. The most obvious fix is to take a light cut on the mating surface of the back plate. The first thing that I noticed that had not been recognized on the initial adjustment, was that instead of having four adjustment screws like a four jaw chuck it had only three. With the three pin D1-3 interface, four adjustment screws might be tricky but should be do able.

    My questions:
    1. Is it normal for this type chuck to use only three adjustment screws?
    2. How much cut would be best. I needed .009 movement and only had .003 clearance?
    3. What type of match marks or orientation indexes are normal for this type thing?
    Byron Boucher
    Burnet, TX

  • #2
    Before you cut anything, have you tried the dowels in a different position?

    Comment


    • #3
      Not sure about yours, but I have a D1-5 spindle and it has an index mark on it so when I installed my Bison six jaw I cleaned everything and inspected it for any particles, installed it, and then indicated it in using a piece of 1" dia Thompson Shaft. I then made a matching index mark in the backplate. I've been using it for two years and it is on and off the spindle regularly and has never been out more than .0003" TIR. The other thing of key importance is to take note and on initial installation and all subsequent installations, tighten the camlocks in the same sequence and manner. I always start at the index mark and go around once to just lightly seat the plate to the spindle, and then go around again and tighten them.

      I would remove yours and inspect it for a stray chip between the plate and spindle if it is that far out. Or possibly the scroll needs cleaning and lube.
      Last edited by Glenn Wegman; 09-12-2009, 08:07 PM.

      Comment


      • #4
        # 1 is a yes some have 3 adj. screws I would take back plate off and clean the pins under the adj. screws and try again before I cut any thing . Those adj. true chucks usually only have about .030 of clearance giving about .015 of adjustment. I have seen the pins wear a spot on the back plate and not adjust good . Again Take apart and look First.
        Every Mans Work Is A Portrait of Him Self
        http://sites.google.com/site/machinistsite/TWO-BUDDIES
        http://s178.photobucket.com/user/lan...?sort=3&page=1

        Comment


        • #5
          Originally posted by Boucher
          When I tried to dial it in it would not adjust very much.
          I had that exact problem myself a few months ago!

          I hate to admit this but.... I have a Bison 6-1/4" 3-jaw on my lathe that I decided to clean out & re-lube awhile back. After re-mounting the chuck (D1-4) I set about dialing it in again. I got it to move a couple thousandths, and no further. I could not understand how this was possible, because I never had a problem before cleaning the chuck, and the machine has never been crashed.

          After a few minutes of some serious head scratching, I finally had the set-tru chuck moving freely with plenty of adjustment, and had no problem getting it centered up.

          It turns out that I had forgotten to loosen the front mounting screws for locking the body down.

          Hey - it happens.....

          Comment


          • #6
            A BUCK type has 4 screws. At least mine does, and it IS a Buck. What "moron" thought it was a good idea to have three?

            Yeah, THAT was a brilliant way of making it easier and much more direct to adjust.............
            1601 2137 5683 1002 1437

            Keep eye on ball.
            Hashim Khan

            If you look closely at a digital signal, you find out it is really analog......

            Comment


            • #7
              Precision surfaces may slowly wear but they NEVER go funky suddenly.

              Look at the registration features the spindle and back plate. You have a chip or something holding things apart. Glide a small slip stone over the face and the conical diameter and see if you feel any "catches". You can tel by the feel and the sound if there is a discontinuity as small as 0.0001" - provided your senses are tuned in. Same deal in the back of the chuck.

              If that doesn't solve the problem take apart the chuck and clean it. Three jaws collect all sorts of small chips and debris passed into the scroll rack in back of the jaws when gripping small diameters or diameters large enough to uncover part of the scroll. These collect and cause mischief. Disassembly and cleaning the three and four jaws chucks is one of those annual chores common to machine shops.

              Grinding jaws, changing out spindle bearings etc are, like tattos, irreversible procedures carrying some surgical risk. Rule out all other sources for error before you take on anything drastic.

              I bet I had a zillion three jaw chucks pass thru my hands over the years and reground the jaws on but three of them. While grinding jaws is very do-able it's only a solution if the scroll is a true spiral and has no local deformations. Chances are, reground jaws are correct only for the diameter they were ground at.
              Last edited by Forrest Addy; 09-14-2009, 10:37 AM.

              Comment


              • #8
                Originally posted by J Tiers
                A BUCK type has 4 screws. At least mine does, and it IS a Buck. What "moron" thought it was a good idea to have three?

                Yeah, THAT was a brilliant way of making it easier and much more direct to adjust.............
                My 8" has four and the 6" has three.

                Never been a problem for ME! Only time I've ever adjusted it is on initial setup or after disassembly and claeaning/lubing. It never seems to need it any other time.

                How often does your Buck need adjusting?

                Comment


                • #9
                  While grinding jaws is very do-able it's only a solution if the scroll is a true spiral and has no local deformations. Chances are, reground jaws are correct only for the diameter they were ground at.
                  While this tired old saw is common, I never thought YOU would trot it out...... because I know you know better.

                  Grinding jaws is NOT FOR CENTERING. NOT NOW, NOT EVER.

                  A three jaw chuck is for convenience, and NOT for precision, unless it is an adjust-tru.

                  NOPE.... grinding jaws is to RETURN THEM TO PARALLEL, allowing them to actually "grip" over their length, and not just "nip" a part in one spot back at the heel of the jaw. It's a way to get some more use out of a chuck that has had the jaw FACES worn bell-mouthed, or otherwise damaged, such as by a "spun" part, etc.

                  It does not fix the scroll, it doesn't have to, you "live with" that or replace the chuck. It doesn't fix worn jaw "ways" in the chuck body or jaws, that's cause for surveying-out the chuck.


                  Originally posted by Glenn Wegman
                  My 8" has four and the 6" has three.

                  Never been a problem for ME! Only time I've ever adjusted it is on initial setup or after disassembly and claeaning/lubing. It never seems to need it any other time.

                  How often does your Buck need adjusting?
                  Rarely..... usually to dial in something of which I need to make a number. For that its nicer than a 4 jaw, IF the dial-in range will do the job. Set up once, run multiple parts through without re-setting. The same spot on the scroll is used, so it's quite precise if the chuck is in usable shape.

                  But its dead easy to do with 4 screws. A person could LEARN to do it with three............. BUT WHY?

                  The net savings to the manufacturer was about 2 minutes of machining to "save the cost of the 4th screw". The net savings to you is that you get to spend more time every time you dial in a part, a net cost.

                  GREAT IDEA..... It's such an advantage that let's make all three jaw chucks have independent jaws......only. Get rid of those useless scrolls.
                  Last edited by J Tiers; 09-14-2009, 10:02 AM.
                  1601 2137 5683 1002 1437

                  Keep eye on ball.
                  Hashim Khan

                  If you look closely at a digital signal, you find out it is really analog......

                  Comment


                  • #10
                    Originally posted by J Tiers
                    Rarely..... usually to dial in something of which I need to make a number. For that its nicer than a 4 jaw, IF the dial-in range will do the job. Set up once, run multiple parts through without re-setting. The same spot on the scroll is used, so it's quite precise if the chuck is in usable shape.

                    But its dead easy to do with 4 screws. A person could LEARN to do it with three............. BUT WHY?

                    The net savings to the manufacturer was about 2 minutes of machining to "save the cost of the 4th screw". The net savings to you is that you get to spend more time every time you dial in a part, a net cost.

                    GREAT IDEA..... It's such an advantage that let's make all three jaw chucks have independent jaws......only. Get rid of those useless scrolls.
                    Agreed that it makes no sense at all! Just not all that bad to adjust if needed.

                    Next time it's apart for a good cleaning it may just get four!

                    I wouldn't be without an adjustable chuck fo every day use!
                    Last edited by Glenn Wegman; 09-14-2009, 10:21 AM.

                    Comment


                    • #11
                      Yeah OK Jerry. Looks like I omitted the other 2200 or so words I usually post whenever the topic of three jaw chucks comes up; the words regarding the care and caveats of three jaw chucks. These words address bell-mouth jaws, slot wear, use of soft jaws, deformation due to collisions, advisability of using three jaw chucks for every-day work, comparative merits of three jaw chucks Vs four jaw, adjustable three jaw chucks, and about another dozen or so topic headings.

                      I guess the few tapics I posted alone constitutes "an old saw" and completely evicerates the merit from my other points. My mistake. I thought I was being brief.

                      And while we are splitting hairs, grinding chuck jaws in place does not make them "parallel". How can three cylindrical arcs distributes about a common center be parallel? (Except in the sense that a line on the cylindrical surface of one jaws if parallel to the axis of its arc is parallel to similar lines on the other two jaws.)

                      Jaw grinding on a three jaw chuck if done right makes their grip cylindrical provided a ring restraint is used at the outer tips of the jaws. This ring restraint preload the jaw in their working position. Thus the jaws to be re-ground (ignoring for the moment the effect of wear) are deflected as if under load, When re-ground and loaded by gripping work at normal chucking forces they form a cylindrical grip.

                      The center plug often reccommended for grinding chuck jaws in place loads the jaws against the scroll but it at best it will not preload the jaws in simulation of their clamped condition. Few people can be convinced that making a restraint ring is worth the effort.

                      The jaws when gently closed on the work would have a back taper. As the operator tightens the chuck the back taper closes down to form a grip having a more or less uniform unit pressure on the gripped surface. But I neglected to include that too.
                      Last edited by Forrest Addy; 09-14-2009, 11:20 AM.

                      Comment


                      • #12
                        Forrest you are the first man in a long time to mention back taper (that actually compensates for a loaded system deflection) in chuck jaws.

                        I found and appreciated your "by cracky brevity" concerning bandsaw wheel crown DIRECTLY to the point. So thought I would ask.

                        I realize that overhang, size, wall thickness, etc. for starters as to parameters for the work piece.
                        THEN the full monte of parameters for the chuck.
                        BUT do you care to speak from experience on how many thou the back taper might be across a jaw length, for that fictitious general work?

                        I once looked at worn jaw work using die shoe pins and took a wild guess at about 1.5 thou and had no complaints.

                        On final pass as the wheel passed beyond the first ticnotch I sorta tapped the cross feed a hair over the next couple or three of ticnotchs until I moved the tool post out that 1.5. I had the spindle speed kinda slow to avoid cramming the wheel.

                        Boi I hope I said that right.

                        Care to comment?

                        Ag

                        Comment


                        • #13
                          Ag

                          In the absense of direct experience all my broad spectrum knowledge stems from "Everything is made of rubber" type aphorisms. These lead me into thought experiments I try in the shop. Sometimes I guess right.

                          How much back taper? Slightly used chuck? M-m-maybe 0.001" times the length of the jaw in inches. Older chucks? More. How much more? Flip a coin, I dunno.
                          Last edited by Forrest Addy; 09-14-2009, 10:19 PM.

                          Comment


                          • #14
                            Originally posted by Forrest Addy

                            I guess the few tapics I posted alone constitutes "an old saw" and completely evicerates the merit from my other points. My mistake. I thought I was being brief.
                            Actually, yes I kinda think it DID gut that bit of the argument, by redirecting it into the argument about improving concentricity, which is what MOST people think grinding does.

                            I'm just tired of others (not you) reciting it from memory every time someone asks about grinding jaws. I think most of them never DID grind any chuck jaws, they are just parroting what someone else said, who probably never did either.



                            And while we are splitting hairs, grinding chuck jaws in place does not make them "parallel". How can three cylindrical arcs distributes about a common center be parallel? (Except in the sense that a line on the cylindrical surface of one jaws if parallel to the axis of its arc is parallel to similar lines on the other two jaws.)
                            yep, that last bit would be correct, as you know.
                            1601 2137 5683 1002 1437

                            Keep eye on ball.
                            Hashim Khan

                            If you look closely at a digital signal, you find out it is really analog......

                            Comment

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