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Re: Videos

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  • montanaaardvark
    I just found a series of 3 videos where he makes his gear and stepper motor mount, ending up putting the gear in place and making it all turn. He appears to
    Message 1 of 41 , Jan 13, 2009
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      I just found a series of 3 videos where he makes his gear and stepper
      motor mount, ending up putting the gear in place and making it all
      turn. He appears to use the Sherline threading set to sync the Z axis
      to the spindle. I think you can get Mach3 to do that (I'm using
      Mach3), so you don't need to have those gears there.

      These appear to be the set, in order - about 1/2 hour of video here.


      Sherline makes a part called a 6500, which is very similar in concept,
      if not execution. http://www.sherline.com/6500pg.htm If I recall
      correctly, they only make them on special order, but they are not that
      expensive. It might be easy to just adapt their design, since it
      seems to use parts on the current DC motor mount.


      --- In SherlineCNC@yahoogroups.com, Martin Dobbins <trainnutz@...> wrote:
      > I think the solution of using a timing belt drive and stepper has
      some promise because it removes the requirement to measure and
      maintain spindle speed and then feed it back into the control software
      in order to cut a thread. 
      > Light cuts would prevent the spindle stepper from bogging down and
      from there it's just a matter of a G code program to sync the spindle
      speed with the feed to produce any number of different threads.  In
      his latest video he cuts an internal 3/4"-16 thread to mate with
      the Sherline spindle nose as he makes an end mill holder from
      scratch.  His third video shows machining an internal thread on what I
      believe is destined to be a dental implant.
      > One of the things I like about these videos from Luiz is he
      updates frequently; he has promised the third and final instalment of
      his endmill holder soon and you can bet it will be posted within the
      next few days.
      > Martin  
      > I'm more interested in the CNC lathe hardware than the machine
      > controller. My attempts at CNC threading have not come out anywhere
      > near that well. The belt drive and stepper on the spindle are obvious
      > improvements I don't have, but I sure could use details on how to
      > thread well with the CNC Sherline.
      > Bob
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    • Fred Smith
      ... started ... mentally ... We tend to think more like a 1/2-13 or 5/8-11 for a limiting size/TPI combination on a Sherline, in steel. ... You still have to
      Message 41 of 41 , Jan 31, 2009
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        > > A 1/4-20 is not a coarse thread for some people.
        > Until last year, I didn't consider it coarse, but when I first
        > trying to thread with CNC, someone here told me it was easier to do
        > finer threads. I understand a bit better why, now, but have
        > filed 1/4-20 away as a "coarse" thread.

        We tend to think more like a 1/2-13 or 5/8-11 for a limiting size/TPI
        combination on a Sherline, in steel.

        > How about if we run slower and take shallower passes? That would
        > reduce the amount of load deceleration going on. The trade off is
        > obviously that it takes longer. As I said, though, I'm a hobbyist.
        > If it takes a few extra minutes to cut a thread that I need to cut
        > once, it doesn't bother me in the slightest.

        You still have to cut with the left side of the tool. The backlash
        is too much to alternate directions and hold a tolerance. In order
        to get enough tool pressure to take a minimum cut, you have to turn
        at a minimum rpm. Each tiny pass will not cut, but only build tool
        pressure until finally a massive chip is removed, drastically slowing
        the spindle, affecting the cut pitch, and probably dropping steps
        left and right.

        Brass and aluminum are more forgiving then steel, but they want to be
        cut at a much higher cutting speed to avoid galling and chip buildup
        on the tool tip.

        > Divide by zero doesn't work for much ;-) I found my spindle was
        > slowing down by around 1% last time. Mach3 syncs to the slower
        > and adjusts the Z axis feed rate very easily with that sort of
        > slowdown.

        You weren't loading the spindle, so yes Mach3 could keep up.

        >The Sherline DC spindle, like most DC motors, has excellent
        > low speed torque.

        Yes DC motors have a near linear torque curve. Put an encoder on one
        and you have a servo motor.

        I would summarize that if you have very tiny threads to cut, you can
        probably get Mach3 to work. That is OK for scale model engine
        fastener creation, but probably not for general purpose kind of
        customized fasteners.

        We are still not going to offer or suport Mach3 threading on a lathe
        because the area where it will work and where it will not is too
        grey, compared with the clear delineation with a high res quadrature
        encoder on the spindle. Maybe once the smooth stepper is out of
        development, it will support a high enough resolution encoder. At
        the present time Mach3 plus a smooth stepper costs more than DeskCNC
        with controller, so it would also be a suboptimal solution.

        Fred Smith - IMService
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