GlossaryKind of term: Manufacturing termAngularity
What is angularity?
Angularity is an orientation tolerance that limits how accurately an inclined surface or axis lies at a theoretically exact angle to a datum.
ISO 1101 classes it as an orientation tolerance, shown as ∠ in the feature control frame. The nominal angle is a basic dimension in a box, 30° for example; the value in the frame is a zone width in millimetres. For an inclined face the zone lies between two parallel planes at that angle to the datum; for an axis with ⌀ in front of the value, the zone is a cylinder. Parallelism and perpendicularity are the special cases at 0° and 90°, each with its own symbol.
What does the standard say about angularity?
ISO 1101 defines the symbol and the zones. The angle has to be given as a theoretically exact dimension, otherwise the nominal orientation is ambiguous. For an inclined axis a second datum may be needed to fix the direction of the zone completely. A plain angle dimension follows different rules: with plus-minus, such as 30° ±0.5°, that tolerance applies, and without one the general angular tolerances of ISO 2768-1 apply when the drawing invokes them.
How does angularity work in practice?
An inclined feature often changes the setup. On a 3-axis machine the part is set at the angle in a sine vice, on an angle plate or in a fixture, which is a separate setup with its own setup time and alignment error. A fourth axis, where the inclination lies about that axis, or a 5-axis machine in 3+2 brings the part or the spindle into position, so the inclined feature can be made in the same setup as other features. The accuracy of the rotary or swivel axes and the machine's calibration then set the error. Which route is cheaper depends on quantity, repeat orders and the machines and workholding available. Inspection is on a coordinate measuring machine aligned to the datums, or with a sine bar and dial indicator on a surface plate.
What is angularity often confused with?
Angularity in a feature control frame is not an angle dimension with plus-minus. 30° ±0.5° gives a tolerance in degrees without a datum, and the allowed deviation in millimetres grows with the length of the face: half a degree over 100 mm comes to almost 0.9 mm. An angularity of 0.05 gives the same zone width along the whole length.
Frequently asked questions
How do you measure angularity?
On a coordinate measuring machine aligned to the datums, or on a surface plate with a sine bar and a dial indicator. The boxed angle is the nominal orientation; what you measure, in millimetres, is how far the face departs from it.
Do I need a 5-axis machine for an angled bore?
Not necessarily. On a 3-axis machine it can be done with an angled setup or a fixture, and on a fourth axis or a 5-axis machine in 3+2 without reclamping. Setup time, repeatability, quantity and the value settle which route fits.