cylindricity

Cylindricity is a geometric tolerance in engineering drawings that specifies how much the surface of a cylindrical feature may deviate from a perfect right circular cylinder. It is a form tolerance that controls the overall cylindrical form rather than size, location, or orientation alone. In GD&T practice, a cylindricity tolerance is defined by a tolerance zone shaped as a right circular cylinder of a stated diameter, coaxial with a datum reference frame. All points on the surface must lie within this zone along the entire length of the feature.

The tolerance combines the effects of straightness of the cylinder’s axis and circularity of its cross-sections. If a datum axis is provided, the axis of the tolerance cylinder is oriented with respect to that datum axis. Otherwise, the axis is defined by the best-fit cylinder to the measured surface. Compliance is evaluated by measuring the surface with a coordinate measuring machine or similar instrument and fitting a cylinder; the maximum radial deviation from the ideal cylinder over the surface is compared to the specified tolerance.

Cylindricity is commonly applied to shafts, bushings, and other components requiring precise straightness and roundness along their length. It is specified in standards such as ISO 1101 and ASME Y14.5, and is distinct from related tolerances like coaxiality and circularity. The result is a single, global form control that ensures the entire cylindrical surface remains within the defined tolerance zone, providing functional assurance for assemblies and mating parts.