GD&T Form and Orientation Tolerances 3 — Questions and Answers
Question 1: What does it mean when a straightness tolerance is applied to the derived median line of a shaft rather than its surface?
- The surface elements must be straight
- Rule #1 is overridden and the shaft axis may bow outside the MMC boundary (Correct answer)
- The shaft must be perfectly round
- The size tolerance is tightened
Correct answer: Rule #1 is overridden and the shaft axis may bow outside the MMC boundary
Straightness of the derived median line overrides Rule #1, allowing the axis to bend outside the perfect-form-at-MMC boundary while the shaft remains within size limits at each cross-section.
Question 2: A parallelism tolerance of 0.05 mm applied to a surface means the surface must lie between two planes that are parallel to the datum and separated by:
- 0.025 mm
- 0.05 mm (Correct answer)
- 0.10 mm
- The size tolerance value
Correct answer: 0.05 mm
The tolerance value of 0.05 mm directly defines the width of the tolerance zone between the two parallel planes.
Question 3: Which orientation tolerance would you use to ensure a drilled hole is exactly 90° to a datum surface?
- Angularity
- Parallelism
- Perpendicularity (Correct answer)
- Tilt
Correct answer: Perpendicularity
Perpendicularity is the orientation tolerance specifically defined for 90° relationships between a feature and a datum.
Question 4: On a GD&T drawing, a circularity tolerance of 0.02 applied to a sphere means:
- Every cross-section through the center must have a roundness within 0.02 (Correct answer)
- The sphere's diameter cannot vary more than 0.02
- The sphere's center must lie within a 0.02 zone
- Every cross-section in one direction must be within 0.02
Correct answer: Every cross-section through the center must have a roundness within 0.02
Circularity on a sphere requires every cross-section passing through the center to be circular within the tolerance value.
Question 5: Which of the following best describes the cylindricity tolerance zone?
- Two coaxial cylinders between which the surface must lie (Correct answer)
- Two parallel planes between which the surface must lie
- A single cylinder the surface must not exceed
- A cone that the surface must fit within
Correct answer: Two coaxial cylinders between which the surface must lie
Cylindricity's tolerance zone consists of two coaxial (same-axis) cylinders; the entire surface must fall between them.
Question 6: An angularity tolerance applied to a hole axis at 45° to a datum controls the hole axis within a:
- Cylindrical zone oriented at 45° to the datum (Correct answer)
- Planar zone oriented at 45° to the datum
- Conical zone at 45°
- Spherical zone centered at 45°
Correct answer: Cylindrical zone oriented at 45° to the datum
When angularity is applied to an axis (feature of size), the tolerance zone is a cylinder oriented at the specified angle to the datum.
Question 7: What is the primary difference between flatness and parallelism?
- Flatness uses a datum; parallelism does not
- Parallelism requires a datum reference; flatness does not (Correct answer)
- Both always require datums
- Neither requires a datum
Correct answer: Parallelism requires a datum reference; flatness does not
Flatness controls a surface's form independently with no datum, while parallelism controls a surface's orientation relative to a referenced datum.
GD&T Form and Orientation Tolerances 3
What does it mean when a straightness tolerance is applied to the derived median line of a shaft rather than its surface?