GD&T Form and Orientation Tolerances 5 — Questions and Answers
Question 1: A drawing specifies flatness of 0.05 on a surface that has a size tolerance of ±0.10. Which statement is true?
- The flatness tolerance is invalid because it exceeds the size tolerance
- The flatness tolerance refines the surface control within the size limits (Correct answer)
- The flatness tolerance replaces the size tolerance
- The size tolerance must be reduced to match the flatness tolerance
Correct answer: The flatness tolerance refines the surface control within the size limits
A flatness tolerance smaller than the size tolerance refines the surface form control; both apply simultaneously and the flatness must be satisfied within the size envelope.
Question 2: On a sheet-metal bracket, a 0.02 straightness tolerance is applied to the top edge (line element). This means each individual line element along the edge must fit between:
- Two parallel planes 0.02 apart
- Two parallel lines 0.02 apart in the plane of measurement (Correct answer)
- A cylinder of diameter 0.02
- Two concentric arcs 0.02 apart
Correct answer: Two parallel lines 0.02 apart in the plane of measurement
Straightness applied to a surface line element creates a 2D tolerance zone of two parallel lines 0.02 apart within the plane of measurement.
Question 3: Which of the following orientation tolerances controls a feature at an angle of exactly 0° to a datum?
- Perpendicularity
- Angularity
- Parallelism (Correct answer)
- Coplanarity
Correct answer: Parallelism
Parallelism is the orientation tolerance for a 0° (parallel) relationship between a feature and its datum.
Question 4: A perpendicularity callout with a diameter symbol (⌀) preceding the tolerance value on an axis means the tolerance zone is:
- A square zone of side equal to the tolerance value
- Two parallel planes perpendicular to the datum
- A cylindrical zone perpendicular to the datum (Correct answer)
- Two parallel planes parallel to the datum
Correct answer: A cylindrical zone perpendicular to the datum
The diameter symbol (⌀) before the perpendicularity tolerance value specifies a cylindrical tolerance zone rather than a two-plane zone.
Question 5: Which GD&T rule states that at Maximum Material Condition (MMC), a feature of size must have perfect form?
- Rule #2 (Regardless of Feature Size)
- Rule #1 (Envelope Principle / Perfect Form at MMC) (Correct answer)
- Taylor Principle
- Bonus Tolerance Rule
Correct answer: Rule #1 (Envelope Principle / Perfect Form at MMC)
Rule #1, the Envelope Principle, requires that a feature of size must have perfect form (no surface variation) when at its MMC boundary.
Question 6: When comparing circularity and cylindricity, which statement is accurate?
- Circularity evaluates the full 3D surface; cylindricity evaluates cross-sections
- Cylindricity evaluates the full 3D surface; circularity evaluates individual cross-sections (Correct answer)
- Both evaluate the same 3D zone
- Cylindricity requires a datum; circularity does not
Correct answer: Cylindricity evaluates the full 3D surface; circularity evaluates individual cross-sections
Cylindricity controls the entire 3D cylindrical surface at once, while circularity only controls individual 2D circular cross-sections one at a time.
Question 7: A form or orientation tolerance callout that includes a free-state modifier (F) indicates the measurement should be taken:
- At maximum material condition
- While the part is restrained in a fixture
- Without any restraining forces applied (in its free state) (Correct answer)
- After heat treatment
Correct answer: Without any restraining forces applied (in its free state)
The free-state modifier indicates the tolerance applies when the part is in its unrestrained, natural condition without any fixturing forces.
GD&T Form and Orientation Tolerances 5
A drawing specifies flatness of 0.05 on a surface that has a size tolerance of ±0.10.
Which statement is true?