Which statement best distinguishes circularity from cylindricity?

Which statement best distinguishes circularity from cylindricity?

• A. Circularity controls the roundness of a circular feature; cylindricity controls the deviation of a cylindrical surface along its axis.
• B. Circularity controls location; cylindricity controls diameter.
• C. Both control only surface finish.
• D. Circularity controls straightness; cylindricity controls flatness.

Answer: (A)

The key idea is that circularity and cylindricity impose different geometric constraints on cylindrical features. Circularity, or roundness, is a 2D tolerance applied to a circular cross-section. It requires that the outline of the cross-section lie within a true circle of the specified diameter. Cylindricity, however, is a 3D tolerance that bounds the entire cylindrical surface within a cylindrical zone coaxial with the feature’s axis. This means cylindricity enforces both the cross-sectional roundness and the straightness of the surface along the length of the feature. So the statement that circularity controls the roundness of a circular feature and cylindricity controls the deviation of a cylindrical surface along its axis accurately captures the distinction: circularity focuses on the shape of a cross-section, while cylindricity governs how far the whole surface can stray from a perfect cylinder along the axis. The other options don’t fit because circularity does not control location, diameter is not the sole concern of cylindricity, and these tolerances are not about surface finish. Also, straightness or flatness are not the primary controls for circularity or cylindricity.

The key idea is that circularity and cylindricity impose different geometric constraints on cylindrical features. Circularity, or roundness, is a 2D tolerance applied to a circular cross-section. It requires that the outline of the cross-section lie within a true circle of the specified diameter. Cylindricity, however, is a 3D tolerance that bounds the entire cylindrical surface within a cylindrical zone coaxial with the feature’s axis. This means cylindricity enforces both the cross-sectional roundness and the straightness of the surface along the length of the feature.

So the statement that circularity controls the roundness of a circular feature and cylindricity controls the deviation of a cylindrical surface along its axis accurately captures the distinction: circularity focuses on the shape of a cross-section, while cylindricity governs how far the whole surface can stray from a perfect cylinder along the axis.

The other options don’t fit because circularity does not control location, diameter is not the sole concern of cylindricity, and these tolerances are not about surface finish. Also, straightness or flatness are not the primary controls for circularity or cylindricity.