GD&T Runout and Concentricity 4 — Questions and Answers
Question 1: What instrument is most commonly used to measure runout in a production environment?
- Coordinate Measuring Machine (CMM) only
- Dial test indicator (DTI) with the part rotating on centers or in a chuck (Correct answer)
- Optical comparator
- Thread plug gauge
Correct answer: Dial test indicator (DTI) with the part rotating on centers or in a chuck
A dial test indicator placed against the surface while the part rotates on centers or in a V-block is the standard production method for measuring runout.
Question 2: If a shaft is bent (curved axis), which runout measurement will show the largest FIM reading?
- Circular runout at the midpoint
- Total runout along the full length (Correct answer)
- Circular runout at either end
- Both circular and total will show identical readings
Correct answer: Total runout along the full length
Total runout captures all cumulative surface deviations including the effect of a bent axis along the entire length, giving the largest FIM reading.
Question 3: Concentricity is removed from ASME Y14.5-2018. What control replaces it for most design intents?
- Runout
- Symmetry
- Position with median points notation
- Coaxiality using position (Correct answer)
Correct answer: Coaxiality using position
ASME Y14.5-2018 removed concentricity and recommends using position applied to the axis (coaxiality) as a more verifiable replacement.
Question 4: A print specifies circular runout of 0.05 mm on a journal bearing surface. The measured FIM at one cross-section is 0.06 mm. What action should be taken?
- Accept the part since one cross-section is not representative
- Reject the part as it exceeds the specified tolerance (Correct answer)
- Re-measure using total runout instead
- Accept only if the average of all cross-sections is under 0.05 mm
Correct answer: Reject the part as it exceeds the specified tolerance
Circular runout must be within tolerance at every cross-section; a single cross-section exceeding 0.05 mm causes rejection.
Question 5: Which of the following best describes the tolerance zone for total runout on a cylindrical surface?
- A series of concentric circles at each cross-section
- Two coaxial cylinders with a radial distance equal to the tolerance value (Correct answer)
- Two parallel planes perpendicular to the datum axis
- A single cylinder centered on the actual axis
Correct answer: Two coaxial cylinders with a radial distance equal to the tolerance value
The total runout tolerance zone for a cylinder is defined by two coaxial cylinders, one inside the other, separated by the stated tolerance value.
Question 6: On a drawing, runout is specified with datum reference A, which is a short cylindrical feature. What concern might an inspector raise?
- Short datum features can be less stable for establishing an accurate axis (Correct answer)
- Runout cannot use cylindrical datums
- Short datums require a higher tolerance value
- The inspector must use CMM for short datum features
Correct answer: Short datum features can be less stable for establishing an accurate axis
Short datum features provide limited constraint for establishing a stable axis, which can introduce uncertainty in the runout measurement.
Question 7: When a face and diameter are used together as compound datums for runout, what geometric relationship do they establish?
- A datum axis perpendicular to a datum plane at a specific point (Correct answer)
- Two parallel planes
- A floating axis with no angular constraint
- A datum center point only
Correct answer: A datum axis perpendicular to a datum plane at a specific point
A compound datum combining a face and diameter establishes a datum axis that is perpendicular to the face and coincident with the diameter's axis.
GD&T Runout and Concentricity 4
What instrument is most commonly used to measure runout in a production environment?