Cylindricity

Controls

All points on an entire cylindrical surface must lie within the annular space between two coaxial cylinders separated by the tolerance value. Cylindricity simultaneously combines circularity (roundness at each slice), straightness (axis deviation) and taper (diameter variation along the length).

It is the most comprehensive form control for cylinders — if cylindricity passes, circularity and axis straightness are implicitly satisfied.

Example

A precision hydraulic piston bore requires cylindricity 0.005. The seal must see a consistent cylindrical surface across its entire stroke — an out-of-round or tapered bore causes the seal to flex unevenly, accelerating wear and eventually causing fluid bypass. Circularity alone would not catch a bore that is round at each slice but tapered end-to-end.

Inspection

• CMM full-surface scan — probe a grid of points across the cylinder and fit minimum zone coaxial cylinders
• Roundness tester with axial traverse — takes circular traces at multiple heights and combines
• Air gauge with multiple sensing positions — fast in-process check for bores
• Cannot be fully verified by manual methods — full-surface coordinate data is required

Datum & Modifiers