CMM measurements are different in different work planes

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  • CMM measurements are different in different work planes

    I am getting a .0012" discrepancy when I measure a diameter in the z plane (probe at A0B0) and when I measure the same diameter in the y plane (A90B0). I used a calibrated ring gage as a specimen and have the PH10T wrist. I am thinking this is software related since Hexagon has recently serviced the CMM and says that it is within a couple microns.

  • #2
    Have you tried re-calibrating?

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    • #3
      Depends on a lot of parameters !
      What probe ? what length ? far from the sphere or not ? what result on the form ? how many hits ? alignment of the ring......
      I don't think about a soft problem...

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      • #4
        I've recalibrated to the point of insanity (same thing over and over expecting different results). I am using a 10mm extension with a 1mmX27.5mm styli. With the ring laying on the CMM granite, I initially level the face of a .500" ring gage and then measure a cylinder in the ring gage to level. Then I measure a circle at -.100" from the face of the ring gage (measurement is .50003). I then fixtured the ring gage in a v-block in the y plane orientation and measured it the same exact ways (same parameters) and the measurement is .4988"

        I can run these two ring gage verification programs on my other two production CMMs and the measurements are within .00015" of each other
        Last edited by edosgood; 03-26-2021, 12:53 PM.

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        • #5
          What about the circularity ?
          I guess your PH10T is misaligned...

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          • #6
            Obvious question, but it's a small probe, are you sure you're not shanking out?
            Automettech - Automated Metrology Technology

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            • JEFMAN
              JEFMAN commented
              Editing a comment
              circularity should answer...

          • #7
            I checked my PH10T alignment and it appears to be good. I tried taking my measurement only .030" into the ring and got the same result (so it is definitely not shaking out)...but there is a lot of form error being reported (.0007"-.001"). I tried a different module and got the same result.

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            • #8
              Originally posted by edosgood View Post
              I checked my PH10T alignment and it appears to be good. I tried taking my measurement only .030" into the ring and got the same result (so it is definitely not shaking out)...but there is a lot of form error being reported (.0007"-.001"). I tried a different module and got the same result.
              Do a graphic analysis of the roundness, is it a 'triangular' pattern? TP20s make a trilobe pattern do to the mechanical switches inside (3-legged switch).
              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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              • #9
                Check the form of both the circle and the cylinder, perhaps the perpendicularity of the cylinder to the face as well. Looking for a difference between the 2.
                sigpicHave a homebrew

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                • #10
                  It does have the trilobal pattern that is characteristic of TP20

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                  • #11
                    Originally posted by edosgood View Post
                    It does have the trilobal pattern that is characteristic of TP20
                    Possible the algorithm used on the Y orientated circle?

                    If it's Max Insc then it would report smaller due to the trilobing.
                    Automettech - Automated Metrology Technology

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                    • edosgood
                      edosgood commented
                      Editing a comment
                      Same algorithm in both programs....

                  • #12
                    Magnetic V-Block ?

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                    • edosgood
                      edosgood commented
                      Editing a comment
                      Definitely no magnetic v-block

                  • #13
                    2 different incidents the other day for me when I was measuring things at different angles. First one was simple 1mm fell off before I realized it 20 minutes later. The other Calibrated three times, even though my results showed good after calibration just taking a single point at the same location at different angles showing .006 different. Before I calibrated it the third time, even though I'm in a "clean room" I rebooted machine and computer, also clean the scales, rehomed the machine, calibrated again and it was within .0002. Not sure what fixed it, but I covered all the simple stuff first.
                    (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
                    They say "Nobody's Perfect." I must be Nobody.

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                    • #14
                      1.jpg 2.jpg 3.jpg I have a trouble with RationalDMIS.When i start software window appear table in Image 1 and 2 .I click Cancel and start software (Image 3).When i measure standard sphere results are different for each different location .
                      Can you help me with this problem ?
                      Attached Files

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                      • vpt.se
                        vpt.se commented
                        Editing a comment
                        Wrong product forum.

                    • #15
                      Can you share a copy of actual hits of both circles ?
                      And a screen shot of circularity ?

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