Question about ASME Y14.5

[A.Drafter]

Hello,

On a recent drawing we put a True Position on a hole location. We accidentally did not use basic dimensions to define the location, but used toleranced dimensions. I was wondering how this would be interpreted. Would the extent of the toleranced dimensions be used to define the location and then in addition the True Position applied to this location? How would this be inspected?

 

[3DDave]

You're on your own. No different that using random numbers instead of letters to write words, there's no documented interpretation. 33 56643 6643544 435 33. See?

 

[Belanger]

According to the standard ASME Y14.5, the position tolerance is meant to control allowable deviation from a "true position" -- and true position is the theoretically exact location given by basic dimensions.
So your scenario doesn't meet the definition of a position tolerance; thus it's nonsensical. (Of course, you said it was just accidental, so the fix would be easy.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems