GD&T Runout and Concentricity 3 — Questions and Answers
Question 1: Which datum reference is required for a runout tolerance callout?
- A datum plane only
- A datum axis (Correct answer)
- A datum point
- No datum is required for runout
Correct answer: A datum axis
Runout tolerances always require a datum axis because the surface elements are measured relative to rotation about that axis.
Question 2: A cylindrical surface has a circular runout tolerance of 0.03 mm and is also controlled by a size tolerance of ±0.1 mm. Which statement is correct?
- Runout automatically overrides the size tolerance
- Both tolerances must independently be satisfied (Correct answer)
- The size tolerance is irrelevant when runout is specified
- Only the tighter of the two tolerances needs to be met
Correct answer: Both tolerances must independently be satisfied
Size and runout are independent controls; a feature must conform to both its size tolerance and its runout tolerance separately.
Question 3: Total runout when applied to a cylindrical surface simultaneously controls which combination of errors?
- Straightness and roundness only
- Cylindricity, coaxiality, and taper (Correct answer)
- Parallelism and perpendicularity only
- Position and angularity of the axis
Correct answer: Cylindricity, coaxiality, and taper
Total runout on a cylinder controls all surface variations including out-of-roundness, wobble, taper, waviness, and coaxiality errors.
Question 4: A part drawing shows a runout callout with two datum references (e.g., A-B). What does this typically indicate?
- The datum axis is established by two datum features used together (Correct answer)
- The runout is measured alternately from datum A then datum B
- Only datum A is used; datum B is a backup
- The tolerance applies to both surfaces simultaneously
Correct answer: The datum axis is established by two datum features used together
Two datum references for runout typically establish a common datum axis from two separate datum features used simultaneously.
Question 5: Why is symmetry sometimes used as an alternative to concentricity for symmetric features?
- Symmetry is easier to apply to non-round features than concentricity (Correct answer)
- Symmetry allows MMC modifiers while concentricity does not
- Symmetry is cheaper to inspect than concentricity
- Symmetry only applies to prismatic features while concentricity applies to round ones
Correct answer: Symmetry is easier to apply to non-round features than concentricity
Symmetry controls the median points of features relative to a datum plane, making it applicable to non-cylindrical symmetric features where concentricity is not appropriate.
Question 6: When inspecting total runout on a stepped shaft, how many dial indicator passes are required?
- One pass across the entire controlled surface (Correct answer)
- One pass per step, each reset to zero
- Two passes — one clockwise, one counterclockwise
- As many passes as there are diameter changes, averaged together
Correct answer: One pass across the entire controlled surface
Total runout requires the indicator to traverse the entire controlled surface in a single continuous sweep while the part rotates.
Question 7: A runout tolerance frame contains the symbol for circular runout and the value 0.02. Where is the leader arrow typically directed?
- To the datum feature
- To the surface being controlled (Correct answer)
- To the center axis of the part
- To the tolerance block in the title block
Correct answer: To the surface being controlled
The feature control frame leader arrow points to the surface being controlled by the runout tolerance, not the datum.
GD&T Runout and Concentricity 3
Which datum reference is required for a runout tolerance callout?