In GD&T, what does cylindricity control require in practice?

In GD&T, what does cylindricity control require in practice?

• A. It requires the combination of circularity and straightness along the axis to bound the surface within a cylinder.
• B. It requires a true position tolerance for the centerline.
• C. It requires flatness of the cylindrical surface.
• D. It controls the concentricity with a datum axis only.

Answer: (A)

Cylindricity measures how closely a cylindrical surface follows an ideal cylinder by requiring the surface to be bounded by a cylinder coaxial with the datum axis. Practically this means enforcing two aspects at once: the cross-sections perpendicular to the axis must be true circles (circularity) and the generators of the cylinder must be straight along the axis (straightness). Together, these conditions ensure every point on the surface lies within a cylinder of the specified diameter, with its axis aligned to the datum axis. The other ideas don’t capture this combined bound. A true position tolerance for the centerline focuses on where the axis is located relative to datums, not how the surface deviates from a cylindrical form. Flatness applies to planar surfaces, not curved cylindrical ones. Concentricity with a datum axis alone controls how the centers align, not the overall radial variation of the cylindrical surface.

Cylindricity measures how closely a cylindrical surface follows an ideal cylinder by requiring the surface to be bounded by a cylinder coaxial with the datum axis. Practically this means enforcing two aspects at once: the cross-sections perpendicular to the axis must be true circles (circularity) and the generators of the cylinder must be straight along the axis (straightness). Together, these conditions ensure every point on the surface lies within a cylinder of the specified diameter, with its axis aligned to the datum axis.

The other ideas don’t capture this combined bound. A true position tolerance for the centerline focuses on where the axis is located relative to datums, not how the surface deviates from a cylindrical form. Flatness applies to planar surfaces, not curved cylindrical ones. Concentricity with a datum axis alone controls how the centers align, not the overall radial variation of the cylindrical surface.