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

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  • chuck
    Steve, Chris original post was not asking for help he made a statement telling us we would need servos if we wanted to do threading of more than 2mm pitch. he
    Message 1 of 15 , Jul 3 2:17 AM
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      Steve,
      Chris' original post was not asking for help he made a statement telling us we would need servos if we wanted to do threading of more than 2mm pitch.
      he was challenged about this statement than appeared to imply that Steve Blackmore had made the statement and that he already knew better which confused many of us I am sure.
      Chuck


      ----- Original Message -----
      From: morerust
      To: mach1mach2cnc@yahoogroups.com
      Sent: Wednesday, July 03, 2013 1:58 AM
      Subject: [mach1mach2cnc] Re: Mach has a small brain for threading on lathe



      The original poster (Chris) is trying to figure out why
      his lathe will not cut 6mm pitch threads. He has stated
      privately that he is able to cut finer threads successfully.
      This naturally leads to the assumption that his machine
      cannot move fast enough to cut a 6mm pitch. This had been
      discussed privately and it seems that it can indeed move
      that fast, but still fails to cut a 6mm thread. I do not
      have a lathe to experiment with and suggested that he
      refer to this list for help because there have been some
      quirks in Mach threading in the past.

      Regards,
      Steve Stallings
      PMDX

      --- In mach1mach2cnc@yahoogroups.com, "chuck" <chuckels@...> wrote:
      >
      > Thanx Steve,
      > my head was ready to explode trying to figure who wrote what.... thought someone slipped something in my drink.....LOL
      > Chuck
      > ----- Original Message -----
      > From: Steve Blackmore
      > To: mach1mach2cnc@yahoogroups.com
      > Sent: Tuesday, July 02, 2013 6:21 PM
      > Subject: Re: [mach1mach2cnc] Mach has a small brain for threading on lathe
      >
      >
      >
      > On Tue, 2 Jul 2013 15:13:20 -0700, you wrote:
      >
      > >Steve:
      > >You don't need a servo motor. You need a lead screw with 4mm pitch and a NEMA 17 will do. I learned the math, when I was six years old!.
      >
      > What the hell were you talking about in your previous post then?
      >
      > Quote
      >
      > "If you want to do thread beyond 2 mm pitch. You must have servo motor
      > or you won't be able to make thread at all you will make the same last
      > thread you ever made. I hope this help those of you whom will visit this
      > some times in future."
      >
      > Try not to post when drunk, drugged or psychotic....
      >
      > Steve Blackmore
      > --
      >
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >





      [Non-text portions of this message have been removed]
    • chris
      ... I have stepper motors on my retro-fit lathe and can machine threads up to 10mm easily (I haven t tried any bigger yet !) here is a video of the lathe
      Message 2 of 15 , Jul 4 3:10 AM
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        --- In mach1mach2cnc@yahoogroups.com, Chris CNC <microcnc_31@...> wrote:

        >
        > If you want to do thread beyond 2 mm pitch. You must have servo motor or you won't be able to make thread at all you will make the same last thread you ever made.

        I have stepper motors on my retro-fit lathe and can machine threads up to 10mm easily (I haven't tried any bigger yet !)

        here is a video of the lathe cutting a 5mm internal thread
        http://www.youtube.com/watch?v=TiFls8kk6eI

        Having said that, it wasn't easy.

        The issue was not with speed, indexing or anything like that..

        ps don't shoot me down because I don't know all the terminology

        The problem was that the threading wizards and G Code that I used all tried to cut the whole thread at once.. In other words, the whole of the threading tool was in contact with the thread at the same time..

        trying to cut a groove with a 13 or 14mm wide contact creates so much drag that no matter how much inertia there is in the lathe, it won't keep speed from one index pulse to the next

        Rather than code a wizard that took nibbles, I chickened out and ground up several tools to cut part of the thread at a time.

        It may be that one of the wizards has code for nibbling away at a thread by taking small cuts.. but I didn't find it.

        Chris
      • John
        ... Box marked first pass depth. Put in here what you want to remove per pass and then under the preview window is a box marked Calculate Number of passes.
        Message 3 of 15 , Jul 4 2:20 PM
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          --- In mach1mach2cnc@yahoogroups.com, "chris" <chris@...> wrote:

          >
          > It may be that one of the wizards has code for nibbling away at a thread by taking small cuts.. but I didn't find it.
          >
          > Chris
          >


          Box marked first pass depth. Put in here what you want to remove per pass and then under the preview window is a box marked "Calculate Number of passes."

          This tells you how many passes to cut the full depth of thread.
        • chris
          ... John, 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
          Message 4 of 15 , Jul 5 2:29 AM
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            --- In mach1mach2cnc@yahoogroups.com, "John" <john@...> wrote:
            >
            >
            >
            > --- In mach1mach2cnc@yahoogroups.com, "chris" <chris@> wrote:
            >
            > >
            > > It may be that one of the wizards has code for nibbling away at a thread by taking small cuts.. but I didn't find it.
            > >
            > > Chris
            > >
            >
            >
            > Box marked first pass depth. Put in here what you want to remove per pass and then under the preview window is a box marked "Calculate Number of passes."
            >
            > This tells you how many passes to cut the full depth of thread.
            >

            John,

            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
          • 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 5 of 15 , Jul 5 3:29 AM
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              > 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 6 of 15 , Jul 5 4:48 AM
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                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 7 of 15 , Jul 5 1:53 PM
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                  --- 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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