2004

560 | Chapter 20 Dimensions and Tolerances
Projected Tolerance Zones
Projected tolerances are specified in addition to positional tolerances to make
the tolerance more specific. For example, projected tolerances control the
perpendicularity tolerance zone of an embedded part.
The symbol for projected tolerance ( ) is preceded by a height value,
which specifies the minimum projected tolerance zone. The projected
tolerance zone height and symbol appear in a frame below the feature
control frame.
Composite Tolerances
A composite tolerance specifies two tolerances for the same geometric char-
acteristic of a feature or for features that have different datum requirements.
One tolerance relates to a pattern of features and the other tolerance to each
feature within the pattern. The individual feature tolerance is more restric-
tive than the pattern tolerance.
In the illustration above, the point where datums A and B intersect is called
the datum axis, the point from which the position of the pattern is calcu-
lated. A composite tolerance could specify both the diameter of the pattern
of holes and the diameter of each individual hole, as in the illustration below.
datum A
datum B