Orientation Tolerances

Orientation tolerances (parallelism, perpendicularity and angularity) are used to control the orientation of a feature (surface or feature of size) with respect to one or more datums. When the orientation tolerances are applied to a feature of size and an MMR or LMR is added, the control of the orientation deviation no longer refers to the median line, but to the entire extracted feature (MMVC boundary), and it should not violate the MMVC virtual condition. The ISO and ASME standards use two different approaches to control the orientation of a feature of size: in order to orient a feature of size, the ISO standards define the concept of extracted median line or median surface. Instead, in the ASME standards, the axis or median plane is used to control the orientation of a feature of size.