Calibration sphere(s) and inspection results

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  • Calibration sphere(s) and inspection results

    Advice please!
    I am inspecting a cylindrical ring gage, size 2.6800" @ xx tolerance, as a test. The ring is within calibration and the cert gives it a .00002" total tolerance. Cool. The cert says it's right on the money. Cool again.
    I wrote a really simple program to inspect the ring. LEVEL and go in and take 5 hits, circle, drop down .200" and take 5 hits, another circle. Simple stuff. Then I copied the program so it is EXACTLY the same with the exception of the program names. The program names are 1) B&S, and then 2) Mitutoyo.
    I did 3 inspections with cal sphere "A" and 3 inspections with cal sphere "B" and came up with slightly different, but consistently different results. Cal sphere "A" gets it .0001" bigger than cal sphere "B" EVERY time!
    I did it like this... calibrate A0B0 with "A" then run the inspection on the ring. Calibrate with "B" then run the inspection on the ring. I repeated this 3 times switching back and forth between the cal artifacts. Every single time the results are within millionths, but .0001" different consistently between the two of them. So we're repeating but something is off.

    This is where I need y'all help. My co-worker states that the "size" of the cal artifact doesn't mean anything at all. All that is important is "form" be correct. I've never even considered this because my artifacts have always measured exactly what is marked on the stems. I measured both with artifacts with a Pratt and Whitney Supermicrometer and I'm certain that "A" is .00015" off from what is marked.

    In PCD, the numbers I put in for size is what is marked on the stems, not what actual measurement is. For whatever that's worth.

    Thoughts??




    -Bill

    PC-DMIS 4.2 MR1 - Global Image 7107 - PH10MQ - SP600M

  • #2
    https://www.pcdmisforum.com/forum/pc...s-significance maybe this might help whats going on when it calibrates

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    • #3
      Originally posted by acgarcia View Post
      https://www.pcdmisforum.com/forum/pc...s-significance maybe this might help whats going on when it calibrates
      Oh thank you VERY much for the link!!! I did try and search but didn't find what I was looking for. This appears to be what I'm looking for Thanks again!
      -Bill

      PC-DMIS 4.2 MR1 - Global Image 7107 - PH10MQ - SP600M

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      • #4
        Both form and size are critical, size mostly because this is how the software calculates features of size. Qual sphere .001 off, your measurements will be some combination of error relating to that.
        Systems Integrator
        Hexagon Manufacturing Intelligence

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        • #5
          Hi PowerJunkie , just a thought about your problem...
          0.0001 inch is 2.54 µm.
          That could be approximately the tolerance of your cmm on the MPEp, or the first term of the tolerance MPEe (old names of errors !).
          In a second time, I believe that a ring gage size is calibrated along 2 perpendicular directions only.
          So you are comparing a circle with an algorithm (Least square ?), measured with 5 hits two the average of 2 dimensions.

          You could calibrate on A and measure B, and then calibrate on B and measure A.
          A nice idea could be taking a third sphere, if you can.

          From "L'Arythmétique du Sire Barrême (1788)" :
          "On doit faire en sorte que le nombre de mesureurs soit impair (...)"
          "Les mesureurs peuvent faire des faux-pas par malice, ignorance ou par négligence (...)"

          ("The Arrhythmic of Sire Barrême (1788)":
          "We must make sure that the number of measurers is odd (...)"
          "Measurers can make missteps through malice, ignorance or negligence (...)")


          In those sentences, you can replace "measurers" by "someone who calibrate the spheres"...
          And then find a company to re-calibrate your spheres !

          Hope this helps, that's only what I think...

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          • #6
            Yes guys, THANK YOU ALL good stuff!!!! I can always count on y'all
            Seriously, this helps me a WHOLE bunch because I did not agree with my co-worker at all.. but he's the alpha here and I need proof before opening my mouth.
            THANKS!!!!
            -Bill

            PC-DMIS 4.2 MR1 - Global Image 7107 - PH10MQ - SP600M

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            • #7
              Be aware, maybe the alpha is already member of this forum :-)

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              • #8
                Dun dun DUNNNNNNNNNN

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