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Burnerd Chuck: Cracked Operating Screw

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  • Burnerd Chuck: Cracked Operating Screw

    A 6" Burnerd 4-Jaw Independent Iron Body Chuck - Series 34 has one operating screw that is cracked.

    The cracks are visible at two of four corners of the broached square wrench socket. They extend from the lip of the mouth down to a depth of one thread. Either it was a simple matter of too much torque applied or maybe the chuck wrench was not fully inserted. Perhaps someone tried to remove the chuck by smacking the wrench.



    The screw turns easily in the chuck and I have been using the chuck as is since it arrived here, taking care to tighten the other screws against this cracked one. While cleaning today, I wondered about repair.

    The operating screws on this chuck appear to be staked in place - I have not studied this closely, but I will assume that the stake can be removed. Replacement of the screw seems to be hampered by a lack of a ready source for another one. A repair of the hardened and ground screw seems limited to shrinking a collar over the lip at the mouth and I do not think this would gain much.

    Any other ideas?

  • #2
    One of my four jaw chucks has screws that look similar to the one shown. There is a key that is inserted in a slot from the rear and that rides in the groove in the center of the threads on the screw. That key is what holds the screw in place.

    Those keys are made from flat, ground steel and have a half round cut in one edge to fit around the groove in the screw. They are a tight fit in the slots in the body of the chuck and are held in place by some set screws that are in holes that were tapped across the boundary between the key and the chuck body. You just remove those set screws and then work the key out - I did say it was a tight fit. Then the screw comes out easily.

    Your Burnerd probably has something similar. A photo of the back side of the chuck, with the mounting plate removed, will probably show the details.

    As for repairing it, perhaps it could be brazed with a steel ring around the neck for reinforcement. Or you could try to purchase an OEM part. I would save making one as a last resort.

    You may also want to braze a reinforcement ring on the other three.
    Paul A.
    SE Texas

    Make it fit.
    You can't win and there IS a penalty for trying!

    Comment


    • #3
      Originally posted by Paul Alciatore View Post
      One of my four jaw chucks has screws that look similar to the one shown. There is a key that is inserted in a slot from the rear

      ... a tight fit in the slots in the body of the chuck and are held in place by some set screws that are in holes that were tapped across the boundary between the key and the chuck body. You just remove those set screws and then work the key out ...

      Your Burnerd probably has something similar. A photo of the back side ...
      The Burnerd looks a little different. There appear to be pressed-in-place slugs.

      Underneath these slugs within the body of the chuck, a U-shaped yoke engages 180؛ of a necked-down section of the operating screw. I do not know whether the yoke is a separate component or machined on the inner end of the slug, I expect the former.

      Although the appearance mumurs "No user-serviceable parts within", drilling/tapping might enable the slug to be extracted - if indeed a pressed fit.



      Comment


      • #4
        I have an 8" PB 4 jaw that has one cracked screw when purchased, but it has hex sockets. I just live with it as the crack is shallow. The ones in your chuck appear to be deeper.

        Perhaps Rotagrip in the UK has a replacement like this one:http://www.rotagriponline.com/index....mart&Itemid=29
        They also have square thread ones for 6" chucks.

        A few years ago I got a set of soft jaws from them for a PB 6", 3 jaw. They did fit after a bit of scraping - then machined them into outside jaws.

        Another solution is to make one - a morning's task!

        Geoff

        Comment


        • #5
          The collar at the end is usually very close in size to the minor diameter of the thread. So I don't think a collar of any usable thickness is a realistic option.

          I'd be leaning towards TIG welding the cracks at the collar and down onto the last thread. And if possible from the inside a short ways into the square recess as well. Done with a light touch and not much time on the joint and a cool down between welding the cracks should provide enough of a repair that thoughtful tightening of the jaw should be possible for years to come.

          In terms of affecting the heat treatment of the screw with care and a fairly rapid on then off for each crack the softening from over heating of the metal should be able to be limited to just the weld and the last thread.
          Chilliwack BC, Canada

          Comment


          • #6
            Originally posted by EddyCurr View Post
            A 6" Burnerd 4-Jaw Independent Iron Body Chuck - Series 34 has one operating screw that is cracked.

            The cracks are visible at two of four corners of the broached square wrench socket. They extend from the lip of the mouth down to a depth of one thread.
            I see the two cracks you mention at 4 and 7 o'clock. It looks like there is another crack starting to form at 2 o'clock.
            Location: Long Island, N.Y.

            Comment


            • #7
              I have a couple of Burnerd 4 jaws like yours which have no locating screw holding the retainer, in my experience they are a slight interference fit, looking from the front you will see a small shoulder sticking up either side of the operating screw using a suitable punch a few alternating taps on these shoulders should see the retainer out.
              I have never seen one drilled out.

              Paul

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              • #8
                I have knocked those retainers out from the front with a forked punch.

                Comment


                • #9
                  same as Paul ^. Once you remove the jaw, you should see a bit of metal on either side of the groove in the screw. These are 2 "prongs" which are part of the plug on the back of the chuck. You can either do as Paul and I did and gently tap the plug out with a punch or drift or you can make a special prong like tool to press on both sides at the same time. Mark the plug and the hole if you're doing more than one. I took my 4 jaw Buck chuck apart to clean out what looked like decades of plastic powder, it was very straightforward.

                  Personally, for the effort involved in fixing that one, I'd just make a new one. PStechpaul did a nice job on his on here, seemed pretty routine as long as you can grind an Acme (square?) thread cutting tool. Don't know if the threads are LH or RH, which might affect your ability to make a new one. Some nice 4140ph and you're good

                  Comment


                  • #10
                    Pratt Burnerd chucks over 4" generally have a circular plug with a forked end for each jaw, it's a light press fit and can easily be driven out from the front, the forks are not hard so use a brass drift. Jaw screws for Imperial chucks are no longer available from the makers. There are at least 2 different sizes of screws for 6" chucks, maybe also for others, check size carefully if buying used or NOS replacements. Dave

                    Comment


                    • #11
                      Originally posted by BCRider View Post
                      The collar at the end is usually very close in size to the minor diameter of the thread. So I don't think a collar of any usable thickness is a realistic option.

                      I'd be leaning towards TIG welding the cracks at the collar and down onto the last thread. And if possible from the inside a short ways into the square recess as well. Done with a light touch and not much time on the joint and a cool down between welding the cracks should provide enough of a repair that thoughtful tightening of the jaw should be possible for years to come.

                      In terms of affecting the heat treatment of the screw with care and a fairly rapid on then off for each crack the softening from over heating of the metal should be able to be limited to just the weld and the last thread.
                      Assuming that this is hardened high carbon/alloy steel part I would be more worried of getting glass hard welds than softening the screw. If going the TIG welding route preheat to 200-300 celsius weld after that.
                      Small tacks and short TIG welds on hardening steel like 1045 without preheat barely hold together the parts in slightest breeze, the weld has strenght of dry cookie.

                      Comment


                      • #12
                        I had a similar problem in a 4 jaw. I tapped down the keepers a little from the front and braised the cracks.
                        It's worked for the last 3 years just fine although I don't use it a lot and am careful when I tighten.
                        I painted that screw red to remind myself.
                        Bill
                        I cut it off twice and it's still too short!

                        Comment


                        • #13
                          Leave the cracks alone.
                          Shrink a sleeve over the spigot
                          to contain the hoop stress
                          and it will keep the cracks tight.
                          No need to even take the screw out.

                          --Doozer
                          DZER

                          Comment


                          • #14
                            Originally posted by MattiJ View Post
                            Assuming that this is hardened high carbon/alloy steel part I would be more worried of getting glass hard welds than softening the screw. If going the TIG welding route preheat to 200-300 celsius weld after that.
                            Small tacks and short TIG welds on hardening steel like 1045 without preheat barely hold together the parts in slightest breeze, the weld has strenght of dry cookie.
                            You're right. I ran into that one time. Welds were cracking open as fast as I could run a bead. I "fixed" it with a good pre-heat and re-running the welds. It stayed together and didn't fail from some flex testing so it came out all right. But it wasn't pretty. So I read you loud and clear on the idea of pre-heating a part of this sort.
                            Chilliwack BC, Canada

                            Comment


                            • #15
                              Originally posted by Doozer View Post
                              Leave the cracks alone.
                              Shrink a sleeve over the spigot
                              to contain the hoop stress
                              and it will keep the cracks tight.
                              No need to even take the screw out.

                              --Doozer
                              Yep, Doozer ( and others) got it right. I would shrink a collar of 4140 on the cracked screw AND the rest of them for good measure. Good luck.

                              Sarge
                              Last edited by sarge41; 02-27-2017, 10:51 AM.

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