Cylindricity ID Card
- General: Cylindricity is a GD&T callout that defines how closely the cylindrical surface of an actual part must match an ideal cylinder. It defines a tolerance zone bounded by two concentric cylinders. The surface of the inspected cylinder must lie within. Cylindricity combines in one callout circularity and straightness.
- GD&T Symbol: ⌭ (Unicode: U+232D)
- Requires Datum: No.
- MMC/LMC: No.
Cylindricity Drawing Example
- The feature control frame can refer to one of the options in the drawing. The meaning is the same.
- The number to the right of the symbol defines the width of the tolerance zone.
- This width can never exceed the width of the dimensional tolerance (0.4 in this example).
Cylindricity Tolerance Zone
- The tolerance zone is the space between two concentric cylinders.
- All imperfections of the cylinder (axial and radial) must be contained within this space.
Measurement
Cylindricity is measured by rotating the part around its axis, while a gauge measures the variation of the surface in several locations along its length. The total variation must be less than the specified tolerance amount.
Cylindricity vs circularity
- While circularity applies to one cross-section at a time and has a circular tolerance zone (2D), the cylindricity tolerance zone spans all cross-sections simultaneously (3D).
- While circularity verifies if a cross-section is a perfect circle, Cylindricity also checks whether the axial portion of a cylinder remains straight.
- Cylindricity can be understood as a combination of circularity and straightness.
Cylindricity vs total runout
At first glance, they may seem almost the same, but there are several key differences:
- Cylindricity is a “form callout”, meaning it does not refer to a datum. It only controls the form of the cylinder and does not influence how it is oriented.
- Runout must refer to a datum and control the cylinder’s form and orientation.
- Cylindricity forms a tolerance zone around the surface of the cylinder.
- Runout forms a tolerance zone around the central axis of the cylinder.
Popular Use Cases
Cylendricity is a popular callout in mechanical and automotive applications. It is often applied to the following mechanical elements: Shafts, Pins, Hydraulic and pneumatic cylinders, Bearings, and Bushings.
