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  • Multi-start threads

    I thought I would start a new topic so as to not clutter the "rolled threads" topic.

    As I mentioned I have a need to lessen the amount of turns required to turn a dial on my reels and it was suggested to use multi-start threads. I appreciate the advice I received from a few members and it prompted me to look on Youtube for a video. I found this one by Stuart de Haro which explains it quite well so I thought I would post it here.



    Ontario, Canada

  • #2
    One of the turning and milling tests in college was a 6” diameter 4 start left hand buttress thread ( as in a 1/4 turn breech block, I was told),
    I missed that one but did watch it done by the instructor ( very adept at multi lever operation as he ran the capstan section too, )
    amazing what can be done with old fashioned heavy iron isn’t it.
    mark

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    • #3
      One way to do it on a manual lathe is to turn the first start, after this is complete advance the compound (set parallel to the spindle) 1/2 the lead without moving the part or disengaging the gearbox, then cut the second start.

      Some CNC lathes have a provision in the software for multiple starts. On a machine that does not simply workshift the Z axis 0 by 1/2 of the lead. As always do not move the part.
      Last edited by Bented; 10-01-2022, 02:36 PM.

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      • #4
        This is a 2 start 1/2-20 thread on a Trak lathe in conversational programming.
        You may only view thumbnails in this gallery. This gallery has 1 photos.

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        • #5
          Originally posted by boslab View Post
          One of the turning and milling tests in college was a 6” diameter 4 start left hand buttress thread ( as in a 1/4 turn breech block, I was told),
          I missed that one but did watch it done by the instructor ( very adept at multi lever operation as he ran the capstan section too, )
          amazing what can be done with old fashioned heavy iron isn’t it.
          mark
          Sounds like a good test, especially for college. Nowadays professional "machinists" couldn't do that.

          I only skimmed through the video, I saved it for later, but it looks like he covered all the basis. Thread dial method is the best, if it works. I have found the end-gearing to be very tedious and error prone. I will use the compound next time the thread dial does not work, unless it is just a massive thread that I cannot infeed.
          21" Royersford Excelsior CamelBack Drillpress Restoration
          1943 Sidney 16x54 Lathe Restoration

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          • #6
            Originally posted by boslab View Post
            ...1/4 turn breech block
            This might be of interest:

            https://d.lib.msu.edu/etd/8139/datas..._mechanism.pdf

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            • #7
              Originally posted by The Metal Butcher View Post
              Thread dial method is the best, if it works. I have found the end-gearing to be very tedious and error prone.
              Proper lathes like a Monarch 10EE had an indexing face/driver/catch plate for this. See:

              http://www.lathes.co.uk/monarch/img12.gif
              from http://www.lathes.co.uk/monarch/page2.html

              Also: https://www.practicalmachinist.com/f...chment.353132/

              There is a book on screwcutting by a Marcus Bowman that suggests that if you have a camlock spindle, you can remove the chuck, rotate it one or more pins and reinstall for multi-start threads. I am highly dubious of this: I am not sure what angular repetition ability the D1 system provides. It is not a documented feature of the specs. Similarly, every D1 camlock chuck I have ever put on has a scribed line on it that you match with one on the spindle so the cam/pin combination is always the same.

              If you clamp a drive dog to the work, you can use the chuck jaws for indexing the thread (but you need to think beforehand about what you do to maintain the same length when you index it). You also need to plan ahead: cutting a two start thread with a drive dog and a three jaw chuck will make you real unhappy about half way through.

              If the stuff is small enough, you could clamp it in an ER square or hex collet block and index that. Push the back of the collet nut against the chuck jaws and length repetition is automatic.


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              • #8
                I have made two twin start threads, the first was for a toolpost for the lathe, and the other was for an electrical connector for a helicopter flotation bag, about 1/2 UNF. That one fooled me at first when the one I made wouldn't screw on, I had made it single start by mistake.
                The easy way for making multi start threads is not to angle the lathe compound, keep it square and then you can use the compound to move the start point for each thread in turn. For a 18 tpi three start thread,you have to set the lathe up for 6tpi.

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                • #9
                  Originally posted by djc View Post
                  Yes, very interesting. Anybody made a stepped interupted thread like the thesis describes?
                  'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                  • #10
                    Originally posted by djc View Post

                    Proper lathes
                    What is a proper lathe?

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                    • #11
                      Too bad you can't use 8mm. There are lots of multistart left and right hand Tr8 taps and dies on AliExpress.

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                      • #12
                        Originally posted by elf View Post
                        Too bad you can't use 8mm. There are lots of multistart left and right hand Tr8 taps and dies on AliExpress.
                        Would you post a link to these taps please, I looked on Aliexpress but couldn't find them?

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                        • #13
                          Originally posted by djc View Post

                          There is a book on screwcutting by a Marcus Bowman that suggests that if you have a camlock spindle, you can remove the chuck, rotate it one or more pins and reinstall for multi-start threads. I am highly dubious of this: I am not sure what angular repetition ability the D1 system provides. It is not a documented feature of the specs. Similarly, every D1 camlock chuck I have ever put on has a scribed line on it that you match with one on the spindle so the cam/pin combination is always the same.
                          If it didn't index closely you wouldn't be able to put the chuck on in any of the three positions. Even if say one hole or one pin was off index, it would still index correctly unless one hole AND on pin was off index. Personally I would expect any camlock chuck to be at least a good as the tolerance on any manually-turned multi-start thread.
                          Peter - novice home machinist, modern motorcycle enthusiast.

                          Denford Viceroy 280 Synchro (11 x 24)
                          Herbert 0V adapted to R8 by 'Sir John'.
                          Monarch 10EE 1942

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                          • #14
                            Yes, but limited by the number of pins. You can't, for example do a 2 start thread using this method on a machine fitted with a D1-3 spindle, or a 3 start on a D1-4.
                            'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                            • #15
                              Does a double start thread have the same clamping force as a single start of the same pitch? Bob

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