ISO 1101 profile of a surface tolerance

The drawing of a composite aerostructure wing component specifies a profile of a surface tolerance of 0.10 A B C over the whole outer skin. The metrologist has to approve the overall 3D conformity of this complex part against the native CAD model.

Principle and inspection of an ISO 1101 profile of a surface tolerance

Type of geometric tolerance	Feature inspected	3D tolerance zone	Measuring instrument
Profile of a surface 0.10	Complex 3D surface	Two boundary surfaces 0.10 mm apart	3D CMM / 3D laser scanner
Profile of a line 0.10	Single 2D section	Two boundary lines 0.10 mm apart	Optical projector / 2D CMM

All values are given for the reference environmental conditions of 20 °C.

3D colour-map comparison with a laser scanner

The check is done by digitising the actual surface with a laser scanner or a CMM probe. The 3D mapping produces a colour map of the normal deviations from the CAD model. To go over 2D profiles, read our guide on the ISO 1101 profile of a line tolerance.

Calculating the profile of a surface deviation

For each measured point, the CMM calculates the normal distance to the theoretical surface. The profile deviation retained is twice the largest absolute value found over the whole surface.

Example: inspecting a nozzle cowl

Cowl toleranced 0.10 A B C. Laser scan of 50,000 points. Largest positive normal deviation: +0.042 mm, largest negative deviation: -0.058 mm. Overall profile deviation = 2 * 0.058 = 0.116 mm. Verdict: the value (0.116 mm) exceeds the 0.100 mm tolerance. The cowl is declared non-conforming.

Shop-floor pitfalls when inspecting a profile of a surface

The first pitfall is a best-fit alignment that hides a location error. The second is the noise filtering of the laser scanner. The third comes from the part sagging under its own weight. To automate your geometric reports, explore CoteCote and our pricing.