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RE: [mach1mach2cnc] Re: Mach has a small brain for threading on lathe

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  • Tony Smith
    ... only ... depth, ... chip, ... spindle ... what ... slightly ... tool ... You cut as much as you can with the CNC, then use a die for the rest. Or buy a
    Message 1 of 15 , Jul 5, 2013
      > Its not the number of passes that is the problem, that works fine, but it
      only
      > controls the depth of each pass. It doesn't matter how many passes you
      > take, and which wizard threading method you choose, as the depth
      > increases, the surface contact of the tool increases.
      >
      > Whichever method of threading is chosen (even alternate flank), the whole
      > of the flank of the tool can be cutting at the same time, and at the full
      depth,
      > both flanks can be in contact. With a big thread that can be very large
      chip,
      > too large to maintain speed accurately enough to live with a single
      spindle
      > index pulse.
      >
      > If sticking with a tool ground to the thread form, then for large threads
      what
      > is needed is code that takes multiple cuts at each depth, each offset
      slightly
      >
      > The alternative would be to use a tool with a more acute angle and cut the
      > thread more like a normal CNC turning operation, roughing out the majority
      > of the metal, then actually following the profile of the thread with the
      tool
      > tip.. It would be a lot slower but give better results.
      >
      > Chris


      You cut as much as you can with the CNC, then use a die for the rest.

      Or buy a more powerful machine.

      Tony
    • Russell Dunn
      ... Or you can even reduce the depth of cut for the last two or three bites. Finish off by repeating the last cut, at perhaps a higher speed to improve the
      Message 2 of 15 , Jul 5, 2013
        On 5 Jul 2013, at 18:29, "Tony Smith" <ajsmith1968@...> wrote:
        >
        > You cut as much as you can with the CNC, then use a die for the rest.
        > Or buy a more powerful machine.
        > Tony
        >


        Or you can even reduce the depth of cut for the last two or three bites. Finish off by repeating the last cut, at perhaps a higher speed to improve the finish.
        I've cut 4mm pitch in Werkstoff 34CrNiMo6 (I think in North America its 4340) with my Maximat using these tricks. Although I must admit that when I CNC'd it, the kaput motor was removed in favour of a 2 kW servo with infinitely variable speed drive and feedback.

        Russell Dunn
        Ferlach,
        Austria

        [Non-text portions of this message have been removed]
      • chris
        ... I think you are missing the point Tony, for cutting big threads it needs a new wizard. It s usable up to about 5mm pitch, but over that the problems occur
        Message 3 of 15 , Jul 5, 2013
          --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@...> wrote:
          >
          > > Its not the number of passes that is the problem, that works fine, but it
          > only
          > > controls the depth of each pass. It doesn't matter how many passes you
          > > take, and which wizard threading method you choose, as the depth
          > > increases, the surface contact of the tool increases.
          > >
          > > Whichever method of threading is chosen (even alternate flank), the whole
          > > of the flank of the tool can be cutting at the same time, and at the full
          > depth,
          > > both flanks can be in contact. With a big thread that can be very large
          > chip,
          > > too large to maintain speed accurately enough to live with a single
          > spindle
          > > index pulse.
          > >
          > > If sticking with a tool ground to the thread form, then for large threads
          > what
          > > is needed is code that takes multiple cuts at each depth, each offset
          > slightly
          > >
          > > The alternative would be to use a tool with a more acute angle and cut the
          > > thread more like a normal CNC turning operation, roughing out the majority
          > > of the metal, then actually following the profile of the thread with the
          > tool
          > > tip.. It would be a lot slower but give better results.
          > >
          > > Chris
          >
          >
          > You cut as much as you can with the CNC, then use a die for the rest.
          >
          > Or buy a more powerful machine.
          >
          > Tony
          >

          I think you are missing the point Tony, for cutting big threads it needs a new wizard. It's usable up to about 5mm pitch, but over that the problems occur

          Dies are not an economical solution over 2 or 3 inches in diameter

          And it would have to be a pretty big machine to make much difference, I was using 4hp geared down on an 10" Taylor chuck (which has plenty of mass)

          I have an 2tpi ACME thread to turn sooner or later, and I'm not looking forward to it.

          Maybe when I get a spare day or two I will take a look, the only wizard I have written so far was for multirib pulleys and that was a lot easier.

          Chris
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