Perpedicularity vrs Runout of a surface back to a cylinder.

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  • Perpedicularity vrs Runout of a surface back to a cylinder.

    I have 2 similar parts. Both have a cylinder as a datum & machined surface at 90° from that cylinder. My question is that 1 part drawing calls out runout of the surface & the other part drawing calls perpendicularity of the surface. (the datum (cyl) is also not a complete diameter, it is in 3 sections). These are my questions

    1.) Should there be a difference in the perp. & runout results? (why 1 on the other)
    2.) I have noticed that if I rotate my part 120° on the CMM fixture & check it I sometimes get different results. Why is this? shouldnt the perp/runout of the part check the same at any orientation? If not why?

    (see attachments)


    Attached Files
    MIKE OXLONG

  • #2
    In answer to question 1, they would be roughly the same, if the surface was probed in a circular pattern. Perpendicularity would be closer to total runout, instead of circular runout as you have on your print.

    In answer to question 2, if you aren't scanning the surface there can be differences in the results because the points probed for the surface, as well as for the cylinder, may not hit the same highs and lows when the part is rotated. If you have an extremely high point density, like a scan, you shouldn't see a difference.
    Last edited by Schrocknroll; 08-17-2017, 09:29 AM.
    PC-DMIS 2016.0 SP8

    Jeff

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    • #3
      I am not using a scanning head. I am using a PH10Mq with a TP20. PCDMISmr2 software.
      MIKE OXLONG

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      • Mikeg
        Mikeg commented
        Editing a comment
        Then its probably like Schrocknroll said because the points probed are going to hit different areas when rotated.

    • #4
      My boss is telling me that the perpendicularity result should be 1/2 of the runout result. I disagree with that.
      MIKE OXLONG

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      • Mikeg
        Mikeg commented
        Editing a comment
        Maybe they think that because perp is similar to total runout vs circular runout

      • RandomJerk
        RandomJerk commented
        Editing a comment
        Maybe they think like that because half the perpendicular value is a smaller number, possibly in "spec", and that means they can ship the part.

      • bfire85
        bfire85 commented
        Editing a comment
        RandomJerk haha that is probably right!

    • #5
      The axial runout seems a little bogus though since you won't have continous surface contact on a 360° rotation...
      PC-DMIS CAD++ 2o19 R1 SP11

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