GD&T - Geometric Dimensioning and Tolerancing Runout and Concentricity Questions and Answers — Questions and Answers
Question 1: An engineer is designing a high-speed rotating shaft that must have minimal vibration. It is critical that the entire cylindrical surface of the shaft remains straight, round, and coaxial with the bearing journals (datums). Which GD&T control is most appropriate to apply to the main body of the shaft?
- Circularity
- Cylindricity
- Total Runout (Correct answer)
- Concentricity
Correct answer: Total Runout
Total runout is the ideal control for this application because it simultaneously controls variations in form (circularity and straightness) and location (coaxiality) for the entire surface relative to the specified datum axis, which directly relates to the dynamic balance and vibration of a rotating shaft.
Question 2: Which of the following statements best describes the primary difference between circular runout and total runout?
- Circular runout can use an MMC modifier, while total runout cannot.
- Circular runout controls the entire surface at once, while total runout controls individual cross-sections.
- Total runout requires a 3D tolerance zone and controls the entire surface, while circular runout uses a 2D zone and controls each circular element independently. (Correct answer)
- Total runout controls only the location of an axis, while circular runout controls only the form of a surface.
Correct answer: Total runout requires a 3D tolerance zone and controls the entire surface, while circular runout uses a 2D zone and controls each circular element independently.
Total runout provides a composite control over the entire feature surface within a 3D tolerance zone. Circular runout, in contrast, applies to each circular element independently, using a 2D tolerance zone at each cross-section without relating one cross-section to another.
Question 3: When inspecting a part, which of the following is a key difference in methodology between measuring Concentricity and measuring Runout?
- Concentricity is measured by finding the full indicator movement (FIM) of a surface, while Runout requires deriving an axis from median points.
- Runout is measured by finding the full indicator movement (FIM) on a surface, while Concentricity requires deriving an axis from the median points of the feature. (Correct answer)
- Runout can only be applied to external features, while Concentricity can be applied to both internal and external features.
- Concentricity is always applied at MMC, while Runout is always applied at RFS.
Correct answer: Runout is measured by finding the full indicator movement (FIM) on a surface, while Concentricity requires deriving an axis from the median points of the feature.
Runout inspection involves placing a dial indicator directly on the feature's surface and rotating the part 360° to measure the Full Indicator Movement (FIM). Concentricity is far more complex to measure, as it requires mapping the surface to determine the location of diametrically opposed points, calculating the median point for each pair, and then verifying that the axis derived from these median points lies within a cylindrical tolerance zone.
Question 4: A feature control frame specifying total runout is applied to the face of a flange that is perpendicular to a central datum axis. What does this tolerance control?
- Only the flatness of the flange face, independent of the datum axis.
- The cumulative variation of perpendicularity and flatness of the flange face. (Correct answer)
- Only the perpendicularity of the flange face to the datum axis.
- The coaxiality of the flange face's outer diameter to the datum axis.
Correct answer: The cumulative variation of perpendicularity and flatness of the flange face.
When total runout is applied to a surface perpendicular to a datum axis (a face), it controls the combined variations of the surface's form (flatness) and its orientation (perpendicularity) relative to the datum axis. Any "wobble" detected during rotation is a result of the cumulative effects of both conditions.
Question 5: According to the ASME Y14.5 standard, what is the shape of the tolerance zone for a concentricity control applied to a cylindrical feature?
- Two parallel planes perpendicular to the datum axis.
- A cylinder whose axis is theoretically coincident with the datum axis. (Correct answer)
- Two coaxial circles at each cross-sectional measurement plane.
- A sphere centered on a datum point.
Correct answer: A cylinder whose axis is theoretically coincident with the datum axis.
The concentricity tolerance specifies a 3-dimensional cylindrical tolerance zone that is perfectly centered on the datum axis. The axis of the controlled feature, which is derived from all median points of the feature's cross-sections, must lie entirely within this cylindrical zone.
Question 6: When total runout is applied to a cylindrical surface relative to a datum axis, it controls the cumulative effect of which geometric variations?
- Circularity, straightness, coaxiality, and taper. (Correct answer)
- Circularity and Profile of a Line only.
- Coaxiality and Perpendicularity only.
- Straightness and Flatness only.
Correct answer: Circularity, straightness, coaxiality, and taper.
Total runout provides a comprehensive 3D control over the entire surface. For a cylinder, this means it controls how round each section is (circularity), how straight the elements are along its length (straightness), how well its axis is aligned with the datum axis (coaxiality), and any uniform change in diameter along the length (taper).
GD&T - Geometric Dimensioning and Tolerancing Runout and Concentricity Questions and Answers
An engineer is designing a high-speed rotating shaft that must have minimal vibration.
It is critical that the entire cylindrical surface of the shaft remains straight, round, and coaxial with the bearing journals (datums).
Which GD&T control is most appropriate to apply to the main body of the shaft?