Orientation Tolerances Do Not Locate.
running into people who are convinced that parallelism locates
surfaces. Not True! On this drawing there is a 22mm
basic dimension that locates the considered surface relative
to datum A. The parallelism tolerance has nothing to do with
this dimension. All three illustrations show a parallelism
tolerance zone. The zone is a pair of parallel planes 0.2mm
apart which remain parallel to the datum simulator (the
surface plate) while floating to "find" the surface. That's
it. The profile of a surface tolerance is what controls the
location of the surface. The 0.5 tolerance is centered on the
basic location of 22mm. The parallelism tolerance floats
inside the profile tolerance.
"find" the surface to determine if the surface is
parallel to the datum simulator regardless of where the
surface is. Only the profile of a surface tolerance uses
the 22mm basic dimension which provides location.
Without the profile tolerance the drawing would be