What is circular runout?

What is circular runout?

• A. A type of runout measured around one cross-section as the part rotates.
• B. A runout measured around the entire circumference of a coaxial feature.
• C. A diameter tolerance for a circle.
• D. A circularity tolerance.

Answer: (A)

Circular runout is a type of runout measured around one cross-section as the part rotates about a datum axis. In practice, you align the datum axis with the feature, rotate the part, and compare the surface at that specific cross-section to a true circle. The radial deviation from that true circle must stay within the specified tolerance for all angles as the part turns, revealing eccentricity or wobble at that particular section. This is different from total runout, which assesses the surface over the entire length as the part rotates. It’s not simply a diameter tolerance, which specifies a size constraint rather than how the surface varies around a circle. And it’s not a circularity tolerance, which constrains the form of the cross-section itself rather than how that cross-section relates to the datum axis during rotation.

Circular runout is a type of runout measured around one cross-section as the part rotates about a datum axis. In practice, you align the datum axis with the feature, rotate the part, and compare the surface at that specific cross-section to a true circle. The radial deviation from that true circle must stay within the specified tolerance for all angles as the part turns, revealing eccentricity or wobble at that particular section.

This is different from total runout, which assesses the surface over the entire length as the part rotates. It’s not simply a diameter tolerance, which specifies a size constraint rather than how the surface varies around a circle. And it’s not a circularity tolerance, which constrains the form of the cross-section itself rather than how that cross-section relates to the datum axis during rotation.