GD&T Form and Orientation Tolerances 2 — Questions and Answers
Question 1: Which GD&T symbol is used to control the straightness of a surface element (line element) on a cylindrical part?
- Flatness (⏥)
- Straightness (⏤) (Correct answer)
- Circularity (○)
- Cylindricity (⌀)
Correct answer: Straightness (⏤)
Straightness controls individual line elements on a surface or the derived median line of a feature of size.
Question 2: A flatness tolerance zone is defined as the space between two:
- Concentric cylinders
- Parallel planes (Correct answer)
- Parallel lines
- Coaxial spheres
Correct answer: Parallel planes
Flatness tolerance zone consists of two parallel planes within which the entire surface must lie.
Question 3: When angularity is applied to a surface, what is the shape of the tolerance zone?
- Two parallel planes at the specified angle to the datum (Correct answer)
- A cylinder at the specified angle
- A cone at the specified angle
- Two parallel lines at the specified angle
Correct answer: Two parallel planes at the specified angle to the datum
Angularity applied to a surface creates a tolerance zone of two parallel planes oriented at the specified angle relative to the datum.
Question 4: Cylindricity differs from circularity in that cylindricity controls:
- Only cross-sectional roundness
- Both the roundness and straightness of the entire surface simultaneously (Correct answer)
- The axis orientation only
- The diameter variation only
Correct answer: Both the roundness and straightness of the entire surface simultaneously
Cylindricity simultaneously controls circularity, straightness, and taper of the entire cylindrical surface in a single tolerance.
Question 5: Which statement about form tolerances and datums is correct?
- Form tolerances always require at least one datum reference
- Form tolerances never reference datums (Correct answer)
- Flatness requires a datum but circularity does not
- Straightness always requires a datum axis
Correct answer: Form tolerances never reference datums
Form tolerances (flatness, straightness, circularity, cylindricity) by definition control the shape of an individual feature and never require datum references.
Question 6: A perpendicularity callout on a pin's axis controls the orientation of the pin's derived median line relative to:
- Its own surface
- A referenced datum plane or axis (Correct answer)
- The part's largest feature
- Any convenient reference
Correct answer: A referenced datum plane or axis
Perpendicularity applied to an axis controls how closely the feature's derived median line is 90° to the referenced datum.
Question 7: Under ASME Y14.5, the circularity (roundness) tolerance value must be:
- Greater than the size tolerance
- Less than or equal to the size tolerance (Correct answer)
- Equal to the cylindricity tolerance
- Independent of the size tolerance
Correct answer: Less than or equal to the size tolerance
Per Rule #1 (Envelope Principle), the circularity tolerance cannot exceed the size tolerance because the feature must remain within its size limits.
GD&T Form and Orientation Tolerances 2
Which GD&T symbol is used to control the straightness of a surface element (line element) on a cylindrical part?