L shape probe giving false readings

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  • L shape probe giving false readings

    Good Morning.
    I am having issues whit an L shape star probe giving false readings. I have 7 angles listed the build A0B0, A90B0, A90B180, A-90B-90, A90B-90, A90B90, A-90B90. I measure a hole with a different probe regular 3mm by 20mm and I get good results but when I use the star probe I get around 1.5mm deviation more than the other probe and the issue happens mainly when the probe is at a 90 angle. any suggestions on what is happening?
    Attached Files

  • #2
    weight?
    sigpicTAU ALPHA PI INDIANA DELTA CHAPTER
    "Due to the highly confidential nature of my job, I am not allowed to know what I am doing" - author unknown

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    • #3
      20 grams

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      • #4
        How long is the tip on the L shape star probe. could be too long? 50mm I think for that probe head. Check on the weight as well.
        sigpicTAU ALPHA PI INDIANA DELTA CHAPTER
        "Due to the highly confidential nature of my job, I am not allowed to know what I am doing" - author unknown

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        • #5
          Originally posted by [email protected] View Post
          Good Morning.
          I am having issues whit an L shape star probe giving false readings. I have 7 angles listed the build A0B0, A90B0, A90B180, A-90B-90, A90B-90, A90B90, A-90B90. I measure a hole with a different probe regular 3mm by 20mm and I get good results but when I use the star probe I get around 1.5mm deviation more than the other probe and the issue happens mainly when the probe is at a 90 angle. any suggestions on what is happening?
          More details please.

          When you say 1.5mm deviation is this in size (diameter), location ? Is the deviation always in the same direction relative to the probe?

          How are you calibrating this probe? Are you aligning with a standard probe then using this probe to measure a specific feature?

          From what I can tell the probe build is legal.

          20-220mm length, 50mm horizontal, weight 33g incl stylus holder. (One thing I'm not sure on is how this carries over to when the probe is indexed at an angle)

          Link to specs on my drop box https://www.dropbox.com/s/k9nkajcx7j...specs.pdf?dl=0


          Automettech - Automated Metrology Technology

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          • #6
            Is the deviation position or hole size?

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            • #7
              the deviation is positional and is in both axis 1.5mm is total tp deviation. The L shape is a 3x20.
              the probe is being calibrated on a ceramic ø24.997 ball at a 90-degree angle.
              the overall length of the probe is 88.6.

              the part is aligned with a standard probe and then I switch to the star pro to measure the hole. the hole I need to measure is on the bottom of the part.

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              • #8
                How is the hole form?

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                • #9
                  is an m8 threaded hole. but laying the part down and using the standard probe the hole is actually in spec.

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                  • #10
                    is the hole measuring round? Are you using pitch when measuring?

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                    • #11
                      FWIW, I've never had much luck rotating a star probe. It has been said it's doable but I often experienced what you are seeing, so I just resorted to alternate methods.
                      Maybe you could probe your cal sphere in A0B0, set your X,Y & Z origin to the center then rotate to A90B0 and probe it again and see if you see the same location deviation. If so, I'd suspect the problem in in the wrist...
                      Sheffield Endeavor3 9.20.8, Tesastar-SM, Leitz LSP-X1s & LSP-X1M, PCDMIS 2011 MR1

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                      • #12
                        Originally posted by [email protected] View Post
                        the deviation is positional and is in both axis 1.5mm is total tp deviation. The L shape is a 3x20.
                        the probe is being calibrated on a ceramic ø24.997 ball at a 90-degree angle.
                        the overall length of the probe is 88.6.

                        the part is aligned with a standard probe and then I switch to the star pro to measure the hole. the hole I need to measure is on the bottom of the part.

                        Are you using the standard probe to define the reference sphere location? Then saying 'No - sphere has not moved' for the L probe? I'm guessing your probes simply aren't properly calibrated in respect to each other.



                        Automettech - Automated Metrology Technology

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                        • #13
                          yes, I use the pitch when measuring a thread.

                          I tried the test with the standard probe and rotating the l shape and still got the same deviation.

                          I always use DCC hits to locate a tool.

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                          • #14
                            Looks like selecting DCC to locate the tool on every probe built was affecting my calibration. right now I ran my master with a manual point to locate tool and for every other probe built I selected NO. My deviations are now microns. thank you to everyone who took the chance to give me feedback.

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                            • NinjaBadger
                              NinjaBadger commented
                              Editing a comment
                              The crucial thing is not manual or DCC, but whether you say the reference sphere has moved.

                              If you use multiple probes, pick one standard probe as your Master probe, this is the only probe you ever say Yes the sphere has moved - and never say 'No it hasn't', even if it hasn't (that's what Yes - DCC is for!).

                              Watch this video where explain what's happening in probe calibration (and explain about using a Master probe)

                              https://www.automettech.com/master-probe-calibration

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