:( I posted bad code

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  • :( I posted bad code

    A while ago I posted code that added a “bonus” acquired from the datum in the form of size deviation to the tolerance zone of the true position tolerance block for a feature. This was done as an alternative to using PCDMIS’s “wiggle” method for people that were frustrated by the 0 TP value it reports. That thread has been deleted and I am posting this to let you know it is not a valid equivalent to the “wiggle” method. Nor is it sound GD&T practice to aquire a “bonus” from the tertiary datum as I coded in the original example. There are also other considerations that should be mentioned. First though I’d like to apologize to anyone who may have adopted this code for the results they may have gotten and would encourage careful consideration be taken by anyone that wishes to practice the technique in it’s original form or even modified from how it was posted.

    My first mistake was to add “bonus” acquired from a tertiary datum. This method becomes flawed by the size variation of the secondary datum. If the secondary datum is at it’s least virtual size then translational movement is 0. The part will only rotate about the secondary and any variation in the tertiary’s actual mating envelope will allow the part to deviate along an arc who’s origin is the secondary datum. As coded I gave it an allowable deviation that is diametrical in shape.

    My next mistake was to add the size difference of the datum’s virtual size and its AME to the tolerance zone of the feature being true positioned. This was a simplified attempt to mimic the part’s movement on a hard gage also known as datum shift. As coded, adding the deviation from MMC to the tolerance zone is not the same as a hard gage. Such code is a complex algorithm that I will not attempt to mimic.

    Although it may be apparent to some it may not have been apparent to all that that code was designed for inside diameters only. For outside features the code would be different.

    As coded in that post, out of tolerance parts could be accepted as in tolerance after “bonus” was applied. Either through misapplying to the tertiary or through mimicking the hard gage improperly or both.

    I am embarrassed to have unintentionally given bad advice and will endeavor in the future to be more prudent in my development of solutions that I post here be they code or otherwise.

    Last edited by craiger_ny; 08-25-2006, 07:52 PM.
    <internet bumper sticker goes here>

  • #2
    Forty lashes with a wet noodle. Don't worry, you caught it. That's all that counts. I don't remember any apologies from WILCOX for some of their pooh-pooh mix ups(official fessing up, not what the WILCOX fellas have owned up to(which we appreciate))

    James Mannes


    • #3
      1404 posts and 1 screw up, a record I'll never beat

      sigpicHave a homebrew


      • #4
        I did not catch it. I should thank Jan D and Kevin Botta for helping me.

        <internet bumper sticker goes here>


        • #5
          This one belongs in the beating yourself off I mean up thread hey Craig.

          I think your posts are some of the most informational and complete answers given even when your documenting you mistakes. Thanks much
          "People demand freedom of speech as a compensation for the freedom of thought, which they seldom use." ~ Soren Kierkegaard


          • #6

            I gave you some more good rep for being adult enough to say I screwed up.

            Like you don't have enough rep now.
            B&S Mistral
            3.207 Beta on XP

            Older'n dirt


            • #7
              Is that Greek, because I don't understand a word of that
              sigpic Life is not a journey to the grave with the intention of arriving safely, but rather a skid in broadside, totally worn, proclaiming WOW What a ride!


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