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  • Bison chuck internal thread not fully cut?

    I just recently picked up a Bison 8" 3-jaw chuck with an integral 2.25"-8 tpi thread to fit my old Logan lathe. The Bison only screws on one thread before it binds up. The thread on the lathe spindle matches my thread gauge perfectly. I checked the thread on the chuck and I can see daylight at the tip and root of the thread gauge. Is it common for the threads in a Bison chuck to be not fully machined to proper depth?

    I'm going to try cleaning these out again to make sure I got all of the crap out of the threads. Maybe its just old shavings and shop crud jamming up the threads.

    If this doesn't work, I imagine I'll have to mount up this new chuck on the lathe and finish the threads. Then I will also have to open up the ledge that registers the chuck to the spindle about 0.025" as it is too small to even fit on the spindle at all. How much clearance should I have between the chuck and the spindle? a couple thou? size on size? a couple tenths?

    Thanks,

    Graydon Stuckey
    Fenton, Mi

  • #2
    Originally posted by Graydon View Post
    I just recently picked up a Bison 8" 3-jaw chuck with an integral 2.25"-8 tpi thread to fit my old Logan lathe. The Bison only screws on one thread before it binds up. The thread on the lathe spindle matches my thread gauge perfectly. I checked the thread on the chuck and I can see daylight at the tip and root of the thread gauge. Is it common for the threads in a Bison chuck to be not fully machined to proper depth?

    I'm going to try cleaning these out again to make sure I got all of the crap out of the threads. Maybe its just old shavings and shop crud jamming up the threads.

    If this doesn't work, I imagine I'll have to mount up this new chuck on the lathe and finish the threads. Then I will also have to open up the ledge that registers the chuck to the spindle about 0.025" as it is too small to even fit on the spindle at all. How much clearance should I have between the chuck and the spindle? a couple thou? size on size? a couple tenths?

    Thanks,

    Graydon Stuckey
    Fenton, Mi
    If you see daylight on the tip and root of the thread that does'n mean much yet. ( you would need to be able to measure the pitch diameter but it's not the easiest thing to do on female thread)
    Try to clean the threads best you can and check the surfaces for nicks or imbedded chips.

    Cutting the existing thread to bigger size is going to be a major pain in the ass so I would triple-check everything before that. Or even see if anyone near you have lathe with similar mounting and see if you can mix and match backplates.

    AFAIK register diameter should be a veery close fit, as close as you can still rotate the parts without getting stuck.

    Comment


    • #3
      As the chuck has integral fitting rather than a separate backplate, it would be best to aim for 0.0005"to 0.001" clearance. Size for size will bind up for sure. It would be advisable to make a plug gauge of the spindle size and bore until it just slides in.
      If things do not turn out well, you could convert the chuck to fit on a backplate. I bought an unused 6" Toolmex four jaw independent chuck with an integral fitting of 1 1/8" for a Myford lathe and modified it to fit a backplate for a 1 3/4" Smart & Brown.
      The advantage of a backplate, is that it can be faced off true before the chuck is fitted.

      Comment


      • #4
        Probably just need to turn a few thou. off the top of the spindle threads.
        Kansas City area

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        • #5
          The Logan has sharp V threads.

          Either take a little off the OD of the threads, or take it out of the chuck threads. One is easier than the other, and makes the threads less easy to "ding".
          1601

          Keep eye on ball.
          Hashim Khan

          Comment


          • #6
            Thank you all for your excellent answers and suggestions.

            Since the spindle thread fits the thread gauge so perfectly, I see what you mean by Sharp V. There's a very large flat on each thread in the chuck.
            I can easily shave a little of the top of the spindle threads. Before I do that, I have a question.

            Is it true that the sole purpose of the threaded spindle is to hold the chuck tightly against the registration collar and that the registration collar holds the chuck concentric and aligned with the spindle? In other words, the thread has no centering function at all? If the answer is "true", then there is no reason not to machine off a few thous clearance on the spindle threads. I just need to make sure I do not touch the registration collar.

            Assuming the first question to be true, then much of my chuck's accuracy will depend on the fit to that registration collar. I would like that to be as close as possible obviously and so I will try to get the fit within a half thou or less.

            I put my Starrett indicator on the spindle and at the end of the spindle and at the registration collar in all axes, the runout was less than a couple tenths. My 5C collett rig also has maybe three tenths of runout on a piece of ground bar stock in the collet. So I think the bearings are pretty good in this old lathe.

            Thank you all very much for your help. I appreciate it.

            Graydon Stuckey
            Fenton, Mi

            Comment


            • #7
              The threaded portion is positioned by the flanks of the thread on both parts. The flank is the flat part between the crest and the root. Taking a bit off the OD won't change anything in terms of how the chuck is positioned on the spindle threads. If you want, you can trim the spindle threads a little at a time, until the crest on the spindle just clears the root on the chuck.
              Kansas City area

              Comment


              • #8
                Originally posted by Toolguy View Post
                The threaded portion is positioned by the flanks of the thread on both parts. The flank is the flat part between the crest and the root. Taking a bit off the OD won't change anything in terms of how the chuck is positioned on the spindle threads. If you want, you can trim the spindle threads a little at a time, until the crest on the spindle just clears the root on the chuck.
                Ah yes, of course. It was 35+ years ago that I was taught that. I had forgotten the importance of that concept in this discussion. Thank you very much.

                Comment


                • #9
                  Originally posted by Graydon View Post
                  Thank you all for your excellent answers and suggestions.

                  Since the spindle thread fits the thread gauge so perfectly, I see what you mean by Sharp V. There's a very large flat on each thread in the chuck.
                  I can easily shave a little of the top of the spindle threads. Before I do that, I have a question.

                  Fenton, Mi
                  Big flat on the chuck side roots or thread tops?
                  If the thread gauge fits perfectly to the spindle but there is visible gap at the chuck side both on thread tops and roots it means in my books that there is no clearance issues at root or thread tops.
                  Now if the thread gauge bottoms on chuck roots and there is gap on the flanks you got an issue.

                  Comment


                  • #10
                    Never heard of threads that would have light at BOTH crest and root with a full V thread gage. BUT there IS a way you could see that.

                    If the thread gage has one side trimmed for the root flat, AND the chuck has full V roots but flats on the ID crests, then you would see what is described.

                    The gage only needs the flats on the part that reaches the root, for cases where the thread root is flattened. The root does not HAVE to be flattened, it is "allowed". The crest HAS TO be flattened, to fit cases where the root is flat. Both on gages and threads.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Originally posted by Graydon View Post
                      Is it true that the sole purpose of the threaded spindle is to hold the chuck tightly against the registration collar and that the registration collar holds the chuck concentric and aligned with the spindle? In other words, the thread has no centering function at all? If the answer is "true", then there is no reason not to machine off a few thous clearance on the spindle threads. I just need to make sure I do not touch the registration collar.
                      i
                      Not true.


                      The spindle is aligned by the threads and the chuck pulled against the the vertical face of the register. The horizontal area (shoulder) is not a register. The thread pitch is concentric to the center line (of course) and that is the register.

                      The only time the shoulder matters is if you have a clamping device that locks the chuck to that like EMCO. In that case you can pull the chuck out of alignment if the shoulder is not a close fit.
                      Last edited by lakeside53; 09-01-2017, 08:43 PM.

                      Comment


                      • #12
                        Originally posted by lakeside53 View Post
                        Not true.


                        The spindle is aligned by the threads and the chuck pulled against the the vertical face of the register. The horizontal area (shoulder) is not a register. The thread pitch is concentric to the center line (of course) and that is the register.

                        The only time the shoulder matters is if you have a clamping device that locks the chuck to that like EMCO. In that case you can pull the chuck out of alignment if the shoulder is not a close fit.
                        Lakeside,

                        OK, then in that case, the outer diameter of the shoulder doesn't really matter that much. I can machine the chuck with a few thou clearance to that shoulder and it should run true because the flanks of the threads are maintaining the concentricity of the chuck with the spindle.

                        Is that correct?

                        Thanks,
                        Graydon

                        Comment


                        • #13
                          Correct!

                          Comment


                          • #14
                            Could be you have an 8 TPI American 60 degree thread and the chuck has a Brit 8 TPI 55 degree thread. Quite common in the UK to find a 9" Southbend 8 TPI x 1.5" backplate does not want to screw on easily onto a Boxford 8 TPI x 1.5" spindle. Difference being the 5 degrees.

                            Comment


                            • #15
                              Originally posted by lakeside53 View Post
                              Not true.


                              The spindle is aligned by the threads and the chuck pulled against the the vertical face of the register. The horizontal area (shoulder) is not a register. The thread pitch is concentric to the center line (of course) and that is the register.

                              The only time the shoulder matters is if you have a clamping device that locks the chuck to that like EMCO. In that case you can pull the chuck out of alignment if the shoulder is not a close fit.
                              It has been my experience that the flank of a screw thread is almost never a valid register. The face of the spindle register will guarantee that the axis of the chuck is parallel to the axis of the spindle. The clearance needed to keep a thread from binding and galling will cause wobble and let the two pieces shift from side to side. The chuck recess that matches the register guarantees that the axis is concentric.

                              To prove it to yourself, take the best screw that you have and screw it onto it's matching screw without tightening it. If you use a pair of vice grips (to magnify the movement) you will see that even a high class nut will wobble on the screw.

                              Dan
                              Last edited by danlb; 09-02-2017, 11:25 AM.
                              At the end of the project, there is a profound difference between spare parts and extra parts.

                              Location: SF East Bay.

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