Angularity

Controls

A surface or axis must lie within a tolerance zone of two parallel planes at a specified basic angle (not 0° or 90°) relative to the datum reference. The zone width equals the tolerance value and is oriented at the exact basic angle.

The nominal angle must always appear as a basic (boxed) dimension on the drawing. Angularity controls orientation only — it does not control the position of the angled feature.

Example

A 30° valve seat chamfer on a fuel injector body must be within 0.03mm to ensure a gas-tight metal-to-metal seal. Angularity is also used on angled oil drillings, bevel gear faces, and chamfered entry features where the precise included angle is critical to function or sealing.

Inspection

• Sine plate or sine bar set to the basic angle + dial gauge swept across the surface
• CMM — measure surface normal vector and compute angle to datum plane
• Precision angle blocks + dial gauge for manual verification
• Air gauge for angled bores where physical access limits dial gauge use

The basic angle is exact — no ± tolerance is applied to the angle itself. The zone width (tolerance value) is what varies.

Datum & Modifiers