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Cutting Metric Theads on a PM1236 lathe

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  • #46
    Originally posted by The Artful Bodger View Post
    This is also true of course for a metric lathe. For example the very common metric CQ6230a (metric version of the PM1236) has a 3mm pitch lead screw and can cut metric pitches .5,.6,.75,1,1.5 and 3mm by engaging the half nuts at any point.
    Quite true. Any sensible choice of lead screw pitch will allow some threads to be cut at any engagement point. This is true in both systems of measure.
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

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    • #47
      hwingo.
      Here is the chart I think you need;-) can any of you confirm that. I was helping out John(aka Bogs, Bogstandard etc) over at the Madmoder with this info. He was so frustrated he allmost returned his lathe before he get this info.



      Best.
      CS

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      • #48
        Crancshafter, that table shows the threading indicator settings for a metric lathe with a 3mm pitch lead screw. The "T" refers to the pinion required to be fitted to the threading indicator. "0" shows the threads that can be cut without use of the threading indicator. "SCALE" shows the indicator marks that can be used with each thread.

        Understanding the "0" table is what confuses people most.

        If I recall correctly John Bogstandard modified his threading indicator to have all three pinions permanently mounted it then being only a matter of moving one screw to get full threading indicator function for metric threads.

        John

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        • #49
          Unless you are making a lead screw a change gear of 127 teeth is just not necessary and while a ratio of 1:2.54 is sought even a much more easily achieved ratio of 1:2.5 will likely be sufficient in most cases and for even greater accuracy than that there are change gear combinations that avoid the inconvenience of a 127 tooth wheel. More here:
          http://conradhoffman.com/metricthreading.htm
          "Patriotism is the last refuge of a scoundrel"

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          • #50
            I just did my first metric thread on my G4003G last week. The machine comes with the needed change gears and the thread chart covers it as well as the owners manual. The 40T headstock gear is swapped for a 35T. The 40T transmission gear is swapped for a 60T and the idler (a double gear) is flipped inside out. For metric the idler gear is no longer an idler as you mesh the headstock gear with the inside teeth and the trans gear with the outside teeth, so it changes the ratio. Easy enough to figure out the ratios from the instructions but there didn't seem to be spacers and offset hubs included in my parts kit to make it work. I made a few spacers and an extended axle shaft to get everything meshed and then it was uneventful from there. The metric thread was around 17.5 tpi so reversing the lathe for successive cuts was almost as fast as using the halfnuts. I saved the parts I made so next time will be easier.

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