GD&T Runout and Concentricity 5 — Questions and Answers
Question 1: A turbine rotor requires tightly controlled vibration during operation. Which GD&T control best addresses dynamic balance concerns related to surface geometry?
- Flatness on the rotor disk
- Total runout on the rotating cylindrical surfaces (Correct answer)
- Parallelism of the shaft ends
- Angularity of the rotor vanes
Correct answer: Total runout on the rotating cylindrical surfaces
Total runout on cylindrical surfaces controls all geometric deviations that contribute to mass imbalance and vibration in rotating equipment.
Question 2: Which statement correctly compares the verification complexity of concentricity versus coaxial position?
- Concentricity is easier because it only needs a dial indicator
- Coaxial position is easier because it can be verified using a functional gauge or CMM axis measurement (Correct answer)
- Both are equally complex to verify
- Position requires more datum references than concentricity
Correct answer: Coaxial position is easier because it can be verified using a functional gauge or CMM axis measurement
Coaxial position (axis-to-axis) can be verified with a functional gauge or CMM axis fit, while concentricity requires finding median points which is mathematically complex.
Question 3: A circular runout symbol (single arrow circle) is placed on a drawing. What is the standard symbol used?
- A circle with a single diagonal arrow (Correct answer)
- Two concentric circles
- A circle with two arrows pointing outward
- A half-circle with an arrow
Correct answer: A circle with a single diagonal arrow
The circular runout symbol in GD&T is a circle with a single diagonal arrow, distinguishing it from total runout which uses a double arrow.
Question 4: For a part with both runout and position callouts on the same surface, which takes precedence?
- Position always overrides runout
- Runout always overrides position
- Both must be independently satisfied; neither overrides the other (Correct answer)
- The tighter tolerance automatically voids the other
Correct answer: Both must be independently satisfied; neither overrides the other
When both runout and position are called out on the same feature, each must be independently verified and satisfied.
Question 5: A design engineer specifies runout instead of cylindricity on a bearing journal. What is a key advantage of this decision?
- Runout is always a tighter control than cylindricity
- Runout relates the surface to a datum axis relevant to function, while cylindricity does not reference a datum (Correct answer)
- Cylindricity cannot be measured in production environments
- Runout allows MMC modifiers that cylindricity does not
Correct answer: Runout relates the surface to a datum axis relevant to function, while cylindricity does not reference a datum
Runout ties surface quality to the functional datum axis (how the part actually rotates), while cylindricity only controls the surface form without a datum reference.
Question 6: What effect does surface roughness have on runout measurement?
- Surface roughness has no effect on runout readings
- High surface roughness can artificially increase the FIM reading beyond actual geometric error (Correct answer)
- Surface roughness only affects total runout, not circular runout
- Rough surfaces reduce FIM readings by absorbing indicator tip movement
Correct answer: High surface roughness can artificially increase the FIM reading beyond actual geometric error
A rough surface can cause the dial indicator tip to bounce or skip, inflating the FIM reading beyond the true geometric runout error.
Question 7: A drawing notes circular runout of 0.04 on a surface WITHOUT a diameter symbol (⌀). What does this imply?
- The tolerance applies to the entire cylindrical surface as total runout
- The tolerance applies to individual cross-sections measured perpendicular to the datum axis (Correct answer)
- The tolerance applies to the end face of the feature
- The tolerance is invalid without a diameter symbol
Correct answer: The tolerance applies to individual cross-sections measured perpendicular to the datum axis
Circular runout without a diameter symbol applies at individual cross-sections perpendicular to the datum axis, which is the standard interpretation of circular runout.
GD&T Runout and Concentricity 5
A turbine rotor requires tightly controlled vibration during operation.
Which GD&T control best addresses dynamic balance concerns related to surface geometry?