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70022Re: [Bulk] RE: [mach1mach2cnc] BackLash.. Finally.!! :)

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  • art
    Mar 1, 2007
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      Hi Paul:

      Thanks fo rthe comments. All true.. Its all a high wire balancing act in the end..


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      ----- Original Message -----
      From: Paul W. Chamberlain
      To: mach1mach2cnc@yahoogroups.com
      Sent: Thursday, March 01, 2007 11:44 AM
      Subject: Re: [Bulk] RE: [mach1mach2cnc] BackLash.. Finally.!! :)

      I think backlash is probably a moot point for machines that have axis
      drive components designed to allow zero mechanical backlash... just
      as the user that only has a parallel port, keyboard and mouse can
      ignore the issues with more elaborate I/O boards and controllers.

      Since Art has thankfully chosen to provide a solution for virtually
      every conceivable CNC driven contraption, there are some machines
      that cannot acheive zero mechanical backlash without complications or
      damage to the axis drive components.

      Many desktop/benchtop machines have factory axis drive leadscrews
      that are conventional thread, or maybe Acme thread, running in a
      metal nut... some of those without backlash adjustment. Aproaching
      <0.001" backlash may cause binding with the slightest variation in
      the leadscrew thread. Also, increased wear of the nut at those
      tolerances compounds the backlash issue run-to-run.

      Most desktop machine manufacturers reccomend 0.002" to 0.005"
      backlash as acceptable for their machines... originally designed for
      manual operation. Upgrading to ballscrews or comparable may be
      difficult due to available space and/or the budget of a hobby class
      operator. Then there are those that would rather make parts... not
      try to build/modify the ultimate machine.

      A classic example I can think of where backlash error shows up is a
      3/8" circular pocket for a press-in bushing, without changing to a
      reamer or boring head. With backlash, there will be steps at the 90
      degree transitions of the arcs. A 1/2" - 1 sec. backlash comp does
      little for this example. I realize the large format gantry routers
      are in a whole different realm where distance and speed are
      concerned. My cudos to Art for trying so hard to allow all of us
      getting what we want... just hope his sanity holds out until we get
      there. ;-)

      For what it's worth... when I was running MPS2003 (DOS) on my Taig,
      backlash comp worked for my circular pocket example. I'm guessing
      that much simpler program didn't even try to address accel/decel
      issues... probably not even aware of servo/encoder systems.

      Paul, Central OR


      --- In mach1mach2cnc@yahoogroups.com, "Mark Vaughan" <mark@...> wrote:
      > The trouble with all this backlash compensation is backlash is play
      in your
      > system.
      > Whether compensation is, or is not required depends on the
      direction of
      > cutting force, whether you are climb or conventional milling.
      > Fine on a lathe where load is normally in the same direction.
      > Because mach offers backlash compensation many diy users will think
      it's OK
      > to build a machine with half an inch of backlash and mach will take
      care of
      > it.
      > We need to all be very careful what we understand can and cannot be
      > with Art's backlash system.
      > There is no substitute here for tight screws. (No pun intended).
      > Dr. Mark Vaughan Ph'D. B.Eng. M0VAU
      > Managing Director
      > Vaughan Industries Ltd, reg in UK no 2561068
      > Water Care Technology Ltd, reg in UK no 4129351
      > Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
      > Phone/Fax 44 1872 561288
      > _____
      > From: mach1mach2cnc@yahoogroups.com
      > On Behalf Of Rich Crook
      > Sent: 01 March 2007 08:08
      > To: mach1mach2cnc@yahoogroups.com
      > Subject: Re: [Bulk] RE: [mach1mach2cnc] BackLash.. Finally.!! :)
      > Umm... I think you've got that backwards.
      > 0.0001 mm is *one tenth* of a micron! A micron is a thousandth of a
      > mm, or .00003937" (just shy of 4 ten thousandths).
      > I'm pretty sure he meant .0001"
      > = Rich =
      > >Art,
      > >Holy shit, 0.0001mm is about 4 microns! Did you have to pawn your
      first and
      > >second born for your glass scales? Are you sure you don't mean
      > >
      > >Andrey
      > >Hi Andy:
      > >
      > >According to my glass scales, the backlash is exact to .0001mm on
      > >system.
      > >Thats about as exact as my system can handle...
      > >
      > >Thanks,
      > >Art
      > >www.artofcnc.ca
      > [Non-text portions of this message have been removed]

      [Non-text portions of this message have been removed]
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