- [Instructor] The location controls provided
by Geometric Dimensioning and Tolerancing standards
improve upon standard plus/minus location tolerancing
by defining circular tolerance zones
and taking into account material conditions
to ensure that the location of features
like holes, slots, bosses, tabs, posts and pins
fall within the widest acceptable range.
The position control defines how much the actual location
of a feature on a part can deviate
from the desired location of that feature.
It is one of the more commonly used
geometric dimensioning and tolerancing controls.
It allows the designer to specify a circular tolerance zone
that a center point axis, or center plane,
must lie within.
The position control can also be used
to define the boundary of a given feature
under maximum material conditions
or least material conditions.
The concentricity control defines
how much the center axis of a cylindrical feature
can deviate from a perfect center axis.
It is strictly defined in the standard
as the condition where the median points
of all diametrically opposed elements
of a surface of revolution
are congruent with the datum axis.
This means that the midpoint of every diameter
drawn through the center of the feature
must not be any further away from the datum axis
than the value specified by the concentricity control.
Symmetry can be thought of as how perfectly a feature
is mirrored about a center plane.
This control limits how much deviation
is allowed from a center plane
to the midpoint of any line drawn perpendicular
to the center plane from one surface of a part
to the opposing surface.