Datum precedence

[Jay_Q]

Just need some clarification. To keep it simple. If I had datum A as a plane, Datum B as a diameter, and Datum C as a point or plane. And the FCF was position to A|B|C. Would the xy origin (assuming z is the A PLN) ALWAYS be on the feature of size (datum B dia.) because it is the secondary? even if some of the basic dimensions show from the datum c, plane or point? I don’t have the new software that takes all the guess work out of it. I’m using 2010

[Schrocknroll]

If [A] is a plane, [B] is a diameter, [C] is a point and the FCF is [A|B|C], then level to A, rotate to B and C, X & Y origin on B, and Z origin on A.

The rule is if a feature can constrain a DOF it must. A can constrain the translation of Z and the rotation around X & Y(leveling) so it must. B can constrain the translation of X and Y so it must. The only thing left is the rotation around Z, so C constrains that.