GD&T - Geometric Dimensioning and Tolerancing Runout and Concentricity 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?

Accepted Answer

Total Runout

Answer

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?

Accepted 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.

Answer

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?

Accepted 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.

Answer

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?

Accepted Answer

The cumulative variation of perpendicularity and flatness of the flange face.

Answer

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?

Accepted Answer

A cylinder whose axis is theoretically coincident with the datum axis.

Answer

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.

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

GD&T - Geometric Dimensioning and Tolerancing Runout and Concentricity Questions and Answers