Question about dimensioning surface profile

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  • Question about dimensioning surface profile

    I've been doing profile of a surface as 2x the absolute value of the worst deviation across a set of points. We have another operator that is showing profile of a surface as your worst T value. I was under the impression that T values were used mostly when working with sheet metal. I am being questioned why I do it one way and the other operator does it this way. I would like to better understand which is the correct way and insure that it is being measured correctly going forward. This is in automotive and using injection molding plastic parts. Any insight or suggestions are welcome. I would like to just figure out which is the correct way and why. I am using PC-Dmis 2018 R1. Attached is an example of what my feature control frame looks like for reference. If any more information is needed I will do my best to clarify. profile feature control frame.PNG

  • #2
    Depends on whether you are dimensioning ISO or ANSI. ISO is 2X the max deviation; whereas ANSI is max positive + max negative together


    • #3
      It would be ISO. Do you have any source I could use for proof when providing my documentation? I've tried looking around and have not really seen anything that would work.


      • neil.challinor
        neil.challinor commented
        Editing a comment
        The ideal "proof" would be the section of the ISO 1101 standard that talks about profile (although you would have to purchase it if you do not already have a copy).

        As a "heads up" brian.freeman mentions in his post that ANSI (ASME Y14.5) has a different interpretation to ISO - this was true for ASME Y14.5 1994. ASME Y14.5 2018 has been updated so that it too essentially reports profile as twice the largest deviation. Although the way ASME word their definition is different to ISO, mathematically it gives the same result.

        With the introduction of the new geometric tolerance command in PC-Dmis 2020 R2, we will support the new way of reporting ASME profile as per ASME Y14.5 2018

      • brian.freeman
        brian.freeman commented
        Editing a comment
        Thanks for the update. I didn't know it has been updated in 2018. Though many (if not all) of our engineering reflects AMSE Y14.5 (1994).
        I'll have to look into it.

    • #4

      So if the other operator is just using the max deviation (T value) from the measured data, I think he is incorrect, or partially correct, he needs to double the value.
      Note: I could be in error.
      But according to all that I have read, ISO is 2 X the max deviation. i.e. (deviation .12 = .24 profile)
      Last edited by brian.freeman; 04-22-2020, 05:40 AM.


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