Using Alignment Features As Datums for Dimensioning

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  • Using Alignment Features As Datums for Dimensioning

    Good Afternoon,

    I have a large cylinder that is Datum A and how 2 smaller cylinders ( 1 on each end) with concentricity call outs to the large cylinder Dat A. In the alignment, I use 5 points and 2 rows to align the the cylinder and define it at Datum A. I also do lots of scanning around the body of the large cylinder and construct the diameter later in the program.

    Which one should I use at datum A? Should I use the cylinder for the alignment or the constructed cylinder?

  • #2
    In my experience leveling to an axis when sampling hits that are not perfectly patterned about the entire part, results in a measurement bias created wherever you have the highest concentration of points. To avoid any bias, I'd make sure whatever A datum you use has equally distributed hits cuts about the whole cylinder, even if that results in just two circular cuts about the ends...


    • EmilySue
      EmilySue commented
      Editing a comment

      Never thought about that, but that would be a really easy way to skew data unintentionally.

    • PH8IL
      PH8IL commented
      Editing a comment
      ah so when management cares more about good numbers than accurate numbers I could go about it like this. lol

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