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cheap DRO from caliper?

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  • Henry Liu
    Has anyone drilled some holes into a caliper and used it as a DRO for the sherline? Seems like a cheap way to get 3 axis DRO. The sherline DRO that they sell
    Message 1 of 7 , Oct 15, 2008
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      Has anyone drilled some holes into a caliper and used it as a DRO for
      the sherline? Seems like a cheap way to get 3 axis DRO. The sherline
      DRO that they sell is rotary so I'm not sure how they compensate for
      backlash.
    • John Dammeyer
      They don t compensate for backlash. Nothing attached to a lead screw can. Only a preloaded ball screw might work well enough. Take a look at the Shumatech
      Message 2 of 7 , Oct 15, 2008
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        They don't compensate for backlash. Nothing attached to a lead screw can.
        Only a preloaded ball screw might work well enough. Take a look at the
        Shumatech DRO 350 if you want to use the Chinese scales with a nice large
        LED readout for a DRO. The kit is not too expensive and has a good user
        group.

        John Dammeyer


        >
        > Has anyone drilled some holes into a caliper and used it as a DRO for
        > the sherline? Seems like a cheap way to get 3 axis DRO. The sherline
        > DRO that they sell is rotary so I'm not sure how they compensate for
        > backlash.
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
        >
      • Henry Liu
        Thanks for the heads up. Backlash can be compensated pretty easily in my own driver routine. I plan on running my cnc through matlab or labview but Mach3 or
        Message 3 of 7 , Oct 15, 2008
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          Thanks for the heads up.

          Backlash can be compensated pretty easily in my own driver routine. I
          plan on running my cnc through matlab or labview but Mach3 or
          something might not have compensation.

          The basic algorithm is:

          while(error<epsilon)
          {
          error=DRO_position-assumed_position;
          assumed_position=error;
          call move_stepper_function(assumed_position)
          }

          The DRO will say what position you are at and output an error. If you
          overshoot, just move back the other direction.

          Thanks for the heads up on the shumatech DRO. They reference cheap
          chinese linear scales but I can't find these on ebay. Anyone know
          where to buy these "cheap chinese scales" Thanks.

          Henry

          On Wed, Oct 15, 2008 at 4:08 PM, John Dammeyer <johnd@...> wrote:
          > They don't compensate for backlash. Nothing attached to a lead screw can.
          > Only a preloaded ball screw might work well enough. Take a look at the
          > Shumatech DRO 350 if you want to use the Chinese scales with a nice large
          > LED readout for a DRO. The kit is not too expensive and has a good user
          > group.
          >
          > John Dammeyer
          >
          >>
          >> Has anyone drilled some holes into a caliper and used it as a DRO for
          >> the sherline? Seems like a cheap way to get 3 axis DRO. The sherline
          >> DRO that they sell is rotary so I'm not sure how they compensate for
          >> backlash.
          >>
          >> ------------------------------------
          >>
          >> Yahoo! Groups Links
          >>
          >>
          >>
          >>
          >>
          >
          >
        • Ron Ginger
          ... Your algorithm for backlash is fine, as long as you have the ability to move the axis with INSTANT acceleration. If less than instant move there will be a
          Message 4 of 7 , Oct 16, 2008
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            >
            > Thanks for the heads up.
            >
            > Backlash can be compensated pretty easily in my own driver routine. I
            > plan on running my cnc through matlab or labview but Mach3 or
            > something might not have compensation.
            >
            >

            Your algorithm for backlash is fine, as long as you have the ability to
            move the axis with INSTANT acceleration. If less than instant move there
            will be a time when the axis is unrestrained and the tool can drag it.
            You will at best leave a divot in the part, at worst you will grab and
            break a tool.

            It is not hard to write an algorithm for backlash, it is not possible to
            make one work correctly. Mathematically easy, just the laws of physics
            that make it hard. This has been tried, and discussed here and on every
            CNC forum or list for several years. Good luck with your algorithm.

            ron ginger
          • alenz2002
            It is not hard to write an algorithm for backlash, it is not possible to make one work correctly. ron ginger Hi Ron, Succinctly stated with a
            Message 5 of 7 , Oct 18, 2008
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              <snip>
              It is not hard to write an algorithm for backlash, it is not possible
              to make one work correctly.
              ron ginger
              <snip>

              Hi Ron,
              Succinctly stated with a keen eye for the obvious!
              Al Lenz
            • Fred Smith
              ... can. The Sherline digital readouts do compensate for backlash: http://www.sherline.com/8100inst.htm The same as most of the currently popular CNC
              Message 6 of 7 , Oct 18, 2008
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                --- In SherlineCNC@yahoogroups.com, "John Dammeyer" <johnd@...> wrote:
                >
                > They don't compensate for backlash. Nothing attached to a lead screw
                can.

                The Sherline digital readouts do compensate for backlash:

                http://www.sherline.com/8100inst.htm

                The same as most of the currently popular CNC controllers compensate
                for backlash.

                We are working on an accessory for our servo systems that will tap into
                the rotary encoders and provide 4 decimal inch readout, screen
                displays. The backlash tracking is part of the process, because, just
                like a CNC'd Bridgeport with a digital readout, which DRO do you
                believe, the one on the controller or the one on the scales?

                Fred Smith - IMService
                http://www.imsrv.com
              • John Dammeyer
                My apologies. The Sherline I played with didn t have the instruction manual for the scales and the backlash compensation was obviously not enabled. That it
                Message 7 of 7 , Oct 20, 2008
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                  My apologies. The Sherline I played with didn't have the instruction
                  manual for the scales and the backlash compensation was obviously not
                  enabled. That it didn't compensate led me to an invalid conclusion.

                  John Dammeyer


                  Automation Artisans Inc.
                  http://www.autoartisans.com/ELS/
                  Ph. 1 250 544 4950


                  > -----Original Message-----
                  > From: SherlineCNC@yahoogroups.com
                  > [mailto:SherlineCNC@yahoogroups.com] On Behalf Of Fred Smith
                  > Sent: Saturday, October 18, 2008 8:29 AM
                  > To: SherlineCNC@yahoogroups.com
                  > Subject: [SherlineCNC] Re: cheap DRO from caliper?
                  >
                  >
                  > --- In SherlineCNC@yahoogroups.com, "John Dammeyer" <johnd@...> wrote:
                  > >
                  > > They don't compensate for backlash. Nothing attached to a
                  > lead screw
                  > can.
                  >
                  > The Sherline digital readouts do compensate for backlash:
                  >
                  > http://www.sherline.com/8100inst.htm
                  >
                  > The same as most of the currently popular CNC controllers compensate
                  > for backlash.
                  >
                  > We are working on an accessory for our servo systems that
                  > will tap into
                  > the rotary encoders and provide 4 decimal inch readout, screen
                  > displays. The backlash tracking is part of the process,
                  > because, just
                  > like a CNC'd Bridgeport with a digital readout, which DRO do you
                  > believe, the one on the controller or the one on the scales?
                  >
                  > Fred Smith - IMService
                  > http://www.imsrv.com
                  >
                  >
                  > ------------------------------------
                  >
                  > Yahoo! Groups Links
                  >
                  >
                  >
                  >
                  >
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