ISO 1101 cylindricity tolerance and its limits

On the drawing of an aircraft engine cylinder liner, the inner surface calls for a cylindricity tolerance of 0.012 mm. The metrologist has to check that the whole actual surface lies between two coaxial cylinders 0.012 mm apart. Cylindricity covers roundness, straightness of the generating lines and parallelism of opposite generating lines all at once.

Definition and measuring methods for a cylindricity tolerance

Geometric error	Covered by cylindricity	Covered by roundness
Ovality / three-lobing	Yes	Yes
Taper / flaring	Yes	No
Axial bending (banana shape)	Yes	No

All values are given for the reference environmental conditions of 20 °C.

Inspecting cylindricity by continuous scanning on a CMM

A rigorous check needs a coordinate measuring machine with a continuous scanning head. The probe follows a tight helix over the full height of the cylinder. To compare with simpler tolerances, read our guide on the difference between circular runout and total runout.

The cylindricity tolerance zone under ISO 1101

Cylindricity is a pure form tolerance on a complete 3D surface. It needs no outside datum axis.

Worked example: inspecting a piston liner

⌀80 mm liner with a 0.012 mm cylindricity tolerance. CMM reading over 100 mm of height: max radius = 40.007 mm, min radius = 39.993 mm. Calculated deviation: 0.014 mm. Verdict: the value (0.014 mm) exceeds the 0.012 mm tolerance by 2 µm. The part is declared non-conforming.

Shop-floor pitfalls when inspecting cylindricity

The first pitfall is treating several separate roundness measurements as a cylindricity check. The second is the springback of a thin-walled part once unclamped. The third comes from thermal drift. To record your specifications, discover our CoteCote dimensional inspection solutions.