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  • Thread Dial Kits

    I few years ago I designed and built a thread dial for my nine inch South Bend lathe. I could see some defects in South Bend original design so I designed them out. The original thread dial gears were straight gears made out of cast iron. I hobbed mine out of bronze so there would be no backlash. On the original South Bend grit and chips could get between the dial face and housing so I designed mine so that could not happen. On my thread dial I wanted to turn as freely as possible so I used a bearing. This makes cutting threads coarser than 8 TPI easier. I also made the dial larger and easier to read than the original.

    Then a couple of years ago I made a bunch of kits consisting of the dial, thread dial gear and a drawing showing how to make the rest of the parts and sold them on the Practical Machinist site and Ebay. I sold out out, but last fall I started getting more requests for these kits so I made a new batch and have a few extra.

    Anyway, I had a long running thread over on the PM site showing how I made these in case if anyone wants to try their hand at making there own. Gary P. Hansen



    This is my thread dial installed on my lathe. I will post some additional photos in another post.
    Last edited by garyphansen; 03-13-2009, 01:00 PM.
    In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

  • #2


    This is one of my hobbed thread dial gears. Because it is hobbed, it has no backlash unless the lead screw is very, very worn.



    Here, I am using a fixture to index and gash a gear blank with a slitting saw in my lathe. Gary P. Hansen
    In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

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    • #3


      This is my hobbing set up. I am using a 8 TPI Acme tap to hob the gear. This gear will work on the South Bend 9N, 10K, 10L and 10R lathes or any lathe that has a RH Acme 8TPI lead screw.



      This is how I cut the index marks on the thread dial. Gary P. Hansen
      In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

      Comment


      • #4
        The thread dials are very nicely made, and would be a good project for the visually challenged or those lacking a thread dial.

        But, a thread dial has little to do with the accuracy of the threads or the ability to cut a particular thread. It is merely a means to indicate when the half nuts can be engaged and being able to engage the half nuts repeatably when cutting odd numbered threads, half threads and such. The half nuts will not engage unless the leadscrew is in the proper spot for engagement. Backlash is a matter of wear in the leadscrew, and it is a good practice to engage the half nuts a few revolutions ahead of the thread to take up any backlash in the system.
        Jim H.

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        • #5
          If there is backlash in the thread dial gear, and you try to engaged the half nuts before the backlash it taken out by the revolution of the lead screw you will cause some extra ware on the half nuts but most likely it will still engage in the right spot and not mess up your threading job. However if you have badly worn half nuts you will need to engage the half nuts one or two reveolutions before the bit comes in contact with the threads to keep the ware in the half nuts from messing up your threads.

          With a 8TPI lead screw you do not need a thread dial to cut 8, 16, 24, 32, 40, 48.56 or 64 TPI. because the half nuts can not engage in the wrong spot. However, if you use a thread dial when cutting those threads you can prevent some ware on your half nuts. Gary P. Hansen
          In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

          Comment


          • #6
            Neat! Some questions from the photos...


            "using a fixture to index and gash a gear blank with a slitting saw"

            --What's in the headstock end?


            "hobbing set up"

            --How tightly do you need to hold the work?


            "This is how I cut the index marks"

            --Would that be considered "broaching"?


            Thanks,

            Gary Fuchs

            Comment


            • #7
              I have a #3MT end mill arbor in the head stock with a slitting saw arbor in that. Because, I do not have a draw bar I have a live center with a cup point pushing up against the slitting saw arbor to keep it seated.

              On the hobbing set up, I have the coupling nut on the top tighten just enough to keep the gear blank from moving up and down but loose enough that the gear blank can still turn freely.

              I would not call it broaching but I an sure some would. Gary P. Hansen
              In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

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              • #8
                Thanks!

                Gary Fuchs

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                • #9
                  Gary - that gashing rig is quite a clever piece of work!

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                  • #10
                    "Gary - that gashing rig is quite a clever piece of work!"

                    A friend built it, I just modified it to work on my lathe and fit my Phase II tool post. Gary P. Hansen
                    In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

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                    • #11
                      Sdgrand sent me a PM and I responded but I am not sure it went through. If it did not Email me at [email protected] Thanks, Gary P. Hansen
                      In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

                      Comment


                      • #12
                        If you look at my photo of my indexing and gear gashing fixture you will noticed that it is attached to my Phase II tool post. That allows me to to raise or lower it to adjust the depth of the cut. Once I had it adjusted right I adjusted the nut so I could always put it back on in the right spot.

                        I have used a tool holder in the Phase II tool post in the past as a milling attachment by clamping the work into the tool holder and adjusting the tool holder up or down. I have a milling attachment for my lathe but some times using the tool holder is faster. It works great on small parts like cutting a notch in a firing pin. Gary P. Hansen
                        In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

                        Comment


                        • #13
                          I have be hobbing some more Thread dial gears today and realized that I should have added some more advice in case anyone wants to try this themselves. As the gear hobbs it will cause the coupling nut to unscrew so I keep my hand on it to prevent it from loosening up. Gary P. Hansen
                          In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

                          Comment


                          • #14
                            This gear will work on the South Bend 9N, 10K, 10L and 10R lathes or any lathe that has a RH Acme 8TPI lead screw
                            Because it is an enveloping worm it will only work on leadscrews that are the same diameter as the South Bend lead screw. The threads per inch of any screw are not tied to the diameter of the screw. If the diameter is larger then the helix angle is smaller and conversely if the diameter is smaller the helix angle is larger. Since it is an enveloping worm wheel it cannot be positioned at an angle to the screw to accomodate a different helix angle.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              Evan: I would have thought that too, but have found that they will work on a lead screw that was 1.25" Diameter 8 Acme threads per inch. That is the largest diameter 8TPI lead screw I know of. I expect that it would work just fine with 1.5" dia Acme 8 thread per inch lead screw. The tap I am using for a hobb is 1" Acme 8 TPI. The South Bend lead screws are 3/4"-8 threads per inch. I think the reason it works is the involute shape of the threads will mesh properly even with different diameters.

                              I discovered this because the first tap I tried was 5/8-8thp Acme. I was not expecting the gear to work with my 3/4" lead screw. I was just trying out hobbing a gear with that tap. To my surprise, the gear it produced worked fine with my 3/4" lead screw. Next, I made my own hobb out of tool steel that was 3/4"-8tpi acme. The gears I made with that hobb worked fine also. Gary P. Hansen
                              In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

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