ISO 1101 profile of a line tolerance
On the drawing of an aircraft turbine blade or a camshaft lobe, the suction-side profile carries a profile of a line tolerance frame of 0.04 A B C. The metrologist has to check that every actual cross-section line stays inside an envelope made of two boundary lines 0.04 mm apart.
Definition and measurement of an ISO 1101 profile of a line tolerance
| Profile specification | Related datums | Tolerance zone | Recommended instrument |
|---|---|---|---|
| Profile of a line 0.04 | None (free form) | Two lines 0.04 mm apart | Optical profile projector |
| Profile of a line 0.04 A B C | Orientation and location datums | Located 2D envelope of 0.04 mm | Scanning CMM |
All values are given for the reference environmental conditions of 20 °C.
Continuous 2D probing and comparison with the CAD file
The line is probed by cutting the profile into a series of 2D sections. The coordinate measuring machine compares the measured coordinates (X, Y) with the theoretical curve from the STEP CAD file. To explore 3D profiles, see our article on the ISO 1101 profile of a surface tolerance.
Unilateral zone or equal on both sides
By default, the 0.04 mm tolerance is split equally (±0.02 mm) about the exact theoretical profile. If the circled U symbol is present, the tolerance is shifted to one side.
Example: inspecting a cam profile
Cam profile toleranced 0.04 A B. CMM scan over 200 2D points. Largest positive deviation found: +0.018 mm, largest negative deviation: -0.025 mm. Equivalent total deviation: 2 * 0.025 = 0.050 mm. Verdict: the value (0.050 mm) exceeds 0.040 mm. The cam does not conform.
Shop-floor pitfalls when inspecting a profile of a line
The first pitfall is misaligning the datum reference frame A B C. The second is using an uncompensated stylus radius. The third comes from probing too few points. To use your CAD files without errors, discover CoteCote and its detection module.