Total Runout Issues

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  • Total Runout Issues

    I attached a very crude sketch of my situation:

    Total Runout of datum -B- (Planar face) to datum -A- (Minor O.D.). CMM measurements are inconsistent in both PC-DMIS and Zeiss Calypso.
    Nobody in the building can show me how to verify on a surface plate....

    The length of -A- is very small compared to it's diameter (about .25" vs 8.5") so locating on -A- is difficult. Not to mention part is very lightweight aluminum.

    Any suggestions on CMM/Plate setup measurements?

    I have CMM doing basic level to -B-, rotate to line formed by holes on -B-, origin XY on -A-, Z on -B-.
    hexq.jpg

  • #2
    You will not get repeatable measurements on a cylinder that short in length on the CMM. Will never happen. I would chuck on the OD, spin it, and run a dial indicator on Datum B to get your runout.

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    • #3
      Originally posted by bfire85 View Post
      You will not get repeatable measurements on a cylinder that short in length on the CMM. Will never happen. I would chuck on the OD, spin it, and run a dial indicator on Datum B to get your runout.
      That's what I was assuming. Thanks bfire85

      Comment


      • #4
        We've got lightweight aluminum parts that I have to check. With very short runouts, I avoid the situation on the CMM. Otherwise, I'll either use nylon toe clamps or double sided tape.

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        • #5
          As has been stated with that callout it is going to be near impossible to get reliable results. If engineering insist on it then you can improve your measurements by using a very short length styli of 10mm, take the same number of hits on the O/D as taken on the equator of the calibration sphere.

          You could also call out the flatness of the face this must be equal to or less than the runout if it is greater then the runout has to be out of specification.

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          • #6
            To add to all this, I would definitely not check the O.D. as a cylinder. CMMs have a hard time solving a cylinder that is so short. Instead measure a circle at each end of the O.D. and construct a 3D line between them. Then check the runout of the face to the line.
            PC-DMIS 2016.0 SP8

            Jeff

            Comment


            • RandomJerk
              RandomJerk commented
              Editing a comment
              If you're going to do this, I'd recommend doing a 6 point cylinder first, leveling to that, then measuring the circles. Not doing this will skew the circles slightly based on the current leveling feature when it doesn't need be.

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