3 Replies Latest reply on Apr 23, 2012 3:15 PM by Steven Winoker

    GD&T

    Steven Winoker

      Am I missing something with respect to some of the GD&T callout symbols not being able to assign a datum letter for such features as flatness, straightness and the other 2 symbols found on the 1st row of SW2011?   All the other rows, the pulldown menu for the datum feature are active.

       

       

      Thanks

        • Re: GD&T
          William Turk

          In the case of flatness and straightness, those features are measured in reference to the surface itself, not another reference surface.  In order to relate a surface to a datum, you need to use parallelism, concentricity, etc.

            • Re: GD&T
              Steven Winoker

              William,

               

              About 10 minutes after asking the question, I received our departments order for The Ultimate GD&T Pocket Guide by Alex Krulikowski.  It's a great reference guide and answered the question why I wasn't pulling up those features.    The fact that these are tolerances of 'form' not 'orientation' is the reason why no datum reference is required.

            • Re: GD&T
              Robert Crawford

              Form tolerances (straightness, flatness, circularity and cylindricity) do not have datum references as they only refer to the surface being toleranced.  Other tolerances (orientation, profile, runout and location) relate one surface to another and thus require a datum reference.