standard deviation error

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  • standard deviation error

    New guy here still learning the ropes...

    I had to buid up a 6x130mm probe to measure a fixture today. There is no other way around it, it needs to be this long to get down into a bottom bushing. My 2x40 and 3x50 probes give me a std dev of .0001 but this probe I built up wont go better than .0006

    I cleaned the tp20 contacts and also used rubbing alcohol on the calibration shere and the tip. Are there any other things I'm missing? I did switch over to a medium force tp20 but no better there either.

    With this kind of error i'm not too confident with my report.
    sigpic

  • #2
    With that length and weight you are going to get some deflection.

    You may try slowing down to a crawl...
    Lately, it occurs to me
    What a long, strange trip it's been.

    2017 R1 (Offline programming)

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    • #3
      Agreed!

      You may be able to mitigate some of the measurement error (after the calibration) by doing your measurements at the same speed you calibrate.

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      • #4
        Originally posted by basselope View Post
        Agreed!

        You may be able to mitigate some of the measurement error (after the calibration) by doing your measurements at the same speed you calibrate.
        You HAVE to do your measurement at the same speed at which you calibrate, otherwise your calibration isn't 'real'. You can check this yourself quite easiely by programming a point, then measure it several times at the calibrate speed, then crank it up and do it again, you WILL see a (big) difference in the results.
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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        • #5
          You're right... once again, poorly worded on my part.

          Your move speed is what you might want to slow down. Quick moves followed by short approaches can leave the whole machine ringing like a bell.

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          • #6
            Originally posted by MJA75 View Post
            New guy here still learning the ropes...

            I had to buid up a 6x130mm probe to measure a fixture today. There is no other way around it, it needs to be this long to get down into a bottom bushing. My 2x40 and 3x50 probes give me a std dev of .0001 but this probe I built up wont go better than .0006

            I cleaned the tp20 contacts and also used rubbing alcohol on the calibration shere and the tip. Are there any other things I'm missing? I did switch over to a medium force tp20 but no better there either.

            With this kind of error i'm not too confident with my report.
            What type of extension?
            The 100 mm. (black color) is very solid. Should have no issues with defection
            sigpicIt's corona time!
            737 Xcel Cad++ v2009MR1....SE HABLA ESPAƑOL

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            • #7
              Originally posted by basselope View Post
              You're right... once again, poorly worded on my part.

              Your move speed is what you might want to slow down. Quick moves followed by short approaches can leave the whole machine ringing like a bell.
              OK, I'll let you off with a warning this time. Next time, TICKET!
              sigpic
              Originally posted by AndersI
              I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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              • #8
                Thanks guys, I got it down to .0004 by reducing the move speed in my program and calibration to 20%. Anything less didnt make it better.

                The extensions I used were a 30mm steel extension, then a 60mm carbon.
                sigpic

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                • #9
                  Originally posted by MJA75 View Post
                  Thanks guys, I got it down to .0004 by reducing the move speed in my program and calibration to 20%. Anything less didnt make it better.

                  The extensions I used were a 30mm steel extension, then a 60mm carbon.
                  I can live with .0004.
                  Gratz!
                  Lately, it occurs to me
                  What a long, strange trip it's been.

                  2017 R1 (Offline programming)

                  Comment


                  • #10
                    I had this problem before, beside reduce the speed I choose user defined calibration option and increase the hits and levels, the deviation will reduce.

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                    • #11
                      I would try to reduce the # of extensions also. I have an 8x150mm ceramic one piece tip and cals under .0002" std dev.
                      I used to be high on life but I built up a tolerance.

                      Brown & Sharpe Global Advantage
                      PCDMIS CAD++ v2011mr2
                      PH10MQ/SP600M


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