∠ Angularity

How to verify

Place the part on the datum and use a master angle block (or a sine plate / sine bar) set exactly to the basic angle as the reference; measure the gap with feeler gauges or a dial indicator along the inclined surface. An optical comparator (profile projector) or optical protractor lets you check the actual angle directly against nominal. On a CMM, the datum is constructed, the basic angle is defined as the theoretical reference, and the linear deviation from that oriented band is evaluated, not the angle in degrees directly.

Workshop guideline values

General

0.05–0.2 mm on chamfers and inclined faces in general machining.

Accuracy

0.02–0.05 mm on parts with a tight functional angle.

High precision

0.005–0.01 mm on cams, inclined guideways or precision parts.

Guidance only: the drawing's value always wins.

Common mistakes when interpreting it

• Reading the tolerance value as if it were an angular tolerance in degrees or minutes: it is always a linear distance (mm) giving the width of the band, not the angle itself.
• Checking the angle with a generic protractor without a known master: without a reference calibrated to the exact basic angle, there is no way to tell whether the error is in the part or in the instrument.