206 GD&T: Application and Interpretation
Copyright Goodheart-Willcox Co., Inc.
Chapter Summary
✓ Datum feature references make it possible
to defi ne toleranced relationships to true
geometric planes and axes.
✓ A datum feature is a physical feature on
a part. Datum features are identifi ed on
drawings and on CAD solid models.
✓ Physical datum features are used to locate
theoretical datum planes, axes (lines), and
points.
✓ References shown in a feature control
frame are made to the physical features that
establish the theoretical datum planes and
axes.
✓ Datum simulators (tools) are used to locate
the theoretical datums from the physical
locations of the datum features on a part or
object.
✓ All datum feature references include material
boundary modifi ers, either implied or
shown.
✓ The number of datum targets used is
dependent on the order of precedence for the
datum.
✓ Multiple feature control frames showing
position or profi le tolerances that reference
the same datum reference frame establish a
single pattern (simultaneous requirements)
of toleranced features.
✓ A secondary or tertiary datum feature
reference including an MMB modifi er results
in a requirement that the datum be simulated
at its applicable maximum material
boundary.
Review Questions
Answer the following questions using a separate sheet
of paper for your answers. Additional review questions
and problems are available with ample workspace in the
Study Guide.
Multiple Choice
1. _____ mutually perpendicular planes form a
complete datum reference frame.
A. Two
B. Three
C. Four
D. Both A and B.
2. A datum reference frame may be thought of
as the theoretical planes and axes that set up
a(n) _____.
A. coordinate system
B. inspection system
C. tooling system
D. feature control frame
3. A fl at datum surface is used to establish a
datum _____.
A. point
B. line
C. area
D. plane
4. A datum axis may be established from a
_____.
A. hole
B. shaft
C. centerline
D. Both A and B.
5. In a drawing view, the leader on a datum
target symbol is made _____ if the target is
on the far side of the feature.
A. dashed
B. solid
C. phantom
D. None of the above.
6. A _____ datum feature reference is always
the fi rst one shown in a feature control
frame.
A. letter A
B. primary
C. secondary
D. tertiary
7. When a datum plane and datum axis are
referenced in the same feature control frame,
_____.
A. the plane must be the primary datum
B. the axis must be the primary datum
C. one of the two is selected as primary
based on design function
D. None of the above.
8. Identifying a cylindrical feature of size as a
datum feature establishes a datum _____.
A. axis
B. plane
C. target
D. symbol