GD&T Runout and Concentricity 2 — Questions and Answers
Question 1: What is the key difference between circular runout and total runout?
- Circular runout applies to a single cross-section while total runout applies along the entire surface (Correct answer)
- Total runout only applies to flat faces while circular runout applies to cylinders
- Circular runout requires a more expensive gauge than total runout
- Total runout is always a tighter tolerance than circular runout
Correct answer: Circular runout applies to a single cross-section while total runout applies along the entire surface
Circular runout measures deviation at individual cross-sections, whereas total runout accumulates error across the entire length of the surface.
Question 2: When a runout tolerance is applied to a conical surface, what does the tolerance zone represent?
- Two coaxial cylinders
- Two parallel planes perpendicular to the axis
- Two lines along the cone surface separated by the tolerance value (Correct answer)
- A cylindrical zone centered on the datum axis
Correct answer: Two lines along the cone surface separated by the tolerance value
For conical surfaces, the runout tolerance zone consists of two lines on the cone surface separated by the tolerance value, measured perpendicular to the surface.
Question 3: A shaft has a total runout tolerance of 0.05 mm. During inspection, the FIM (Full Indicator Movement) reading is 0.04 mm. The part is:
- Rejected because FIM must be exactly equal to the tolerance
- Accepted because the FIM is within the 0.05 mm tolerance (Correct answer)
- Rejected because total runout requires zero FIM
- Accepted only if re-measured on a different datum
Correct answer: Accepted because the FIM is within the 0.05 mm tolerance
The part passes because the measured FIM of 0.04 mm is less than the specified total runout tolerance of 0.05 mm.
Question 4: Concentricity is most accurately described as a control of:
- Surface elements relative to a datum axis
- The median points of diametrically opposed surface elements relative to a datum axis (Correct answer)
- The center of a circle relative to a datum plane
- The axis of a cylinder relative to a datum surface
Correct answer: The median points of diametrically opposed surface elements relative to a datum axis
Concentricity controls the location of the derived median points of all diametrically opposed surface elements, not the surface itself.
Question 5: Which of the following characteristics makes concentricity difficult to verify?
- It requires specialized runout equipment not commonly found in shops
- It requires deriving median points from opposing surface elements rather than direct surface measurement (Correct answer)
- It cannot be measured on a surface plate
- It requires the part to be rotating during inspection
Correct answer: It requires deriving median points from opposing surface elements rather than direct surface measurement
Finding median points of diametrically opposed elements requires complex calculations, making concentricity verification more difficult than runout.
Question 6: A designer wants to control wobble of a rotating disk face. Which GD&T control is most appropriate?
- Flatness
- Circular runout applied to the face (Correct answer)
- Concentricity
- Parallelism
Correct answer: Circular runout applied to the face
Circular runout applied to a face (axial runout) directly controls wobble of a rotating surface relative to a datum axis.
Question 7: In GD&T, what does MMC (Maximum Material Condition) bonus tolerance apply to for runout callouts?
- Runout tolerances can use MMC modifiers on the datum feature
- MMC bonus tolerance is not applicable to runout tolerances (Correct answer)
- Runout tolerances always use MMC on the controlled feature
- MMC applies to runout only for external features
Correct answer: MMC bonus tolerance is not applicable to runout tolerances
Runout is a surface control and cannot use MMC or LMC modifiers because it applies directly to surfaces, not to axes or center planes.
GD&T Runout and Concentricity 2
What is the key difference between circular runout and total runout?