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A common
error on drawings is to apply only angularity to features that
are not perpendicular or parallel to the datum reference
frame. The most important characteristic to control is
location. Position locates features of size. Profile of a
surface is the only geometric tolerance that locates surfaces.
The orientation tolerances of perpendicularity, parallelism
and angularity never locate features. The angled surfaces on
this part, for instance, need to be located relative to the
datum reference frame. If only angularity had been applied,
the drawing would be incomplete. Profile of a surface locates
the surfaces in addition to controlling the angularity. If the
orientation of these surfaces needs to be better than the
orientation provided by the profile of a surface tolerance, an
angularity tolerance may be added as a refinement. Locate
first-refine second. |
