⌓ Profile of a surface
Profile of a surface · Perfil · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
The whole 3D surface must lie within a 0.2 mm envelope around the theoretical model (CAD or basic dimensions), relative to the A, B and C datum reference frame.
What controls
Controls the form of a complete surface (not just one section) relative to the theoretical three-dimensional model (CAD or basic dimensions), and can replace several form, orientation and location tolerances with a single requirement if the drawing explicitly says so (profile as a composite tolerance). The tolerance zone is an envelope of constant thickness around the entire nominal surface.
How to verify
The standard method on complex 3D parts is an optical or structured-light scanner that captures the complete point cloud and automatically compares it against the nominal CAD model, producing a color map of the deviations. A CMM with point-by-point probing (or a continuous scanning probe) gives more accurate but slower results on large surfaces. Always check that the comparison software uses the same datum reference frame as the drawing, not the CAD model origin as is: a perfect surface that is misaligned in the comparison looks out of profile when it is not.
tolerance zone
Envelope of constant thickness around the entire nominal 3D surface (CAD or basic dimensions).
Datums and notes
Without datums it controls only the form of the surface; with datums (|A|B|C|) it controls form, orientation and location in a single requirement, which is why it can replace several tolerances. That is why the comparison software must align to the drawing's datum reference frame and not to a best fit of the point cloud.
Workshop guideline values
- General
- 0.15–0.4 mm on 3D surfaces of castings or general machining.
- Accuracy
- 0.05–0.1 mm on tight functional surfaces.
- High precision
- 0.01–0.03 mm on precision molds or aerospace parts.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Comparing the scanned point cloud against the CAD model origin as is, without first aligning to the drawing's datum reference frame: a perfect surface that is misaligned in the comparison looks out of profile when it is not.
- Assuming profile of a surface automatically replaces form, orientation and location: it only does so if the drawing explicitly specifies it as a composite tolerance; otherwise those still apply separately.
How to get it in the workshop / if it comes out of tolerance
Very powerful: it can replace several form, orientation and location tolerances if the drawing says so. Common on castings, molds and sculpted parts.
On complex 3D surfaces, first compare the CAM program against the CAD model: too large a stepover or machining tolerance (chordal tolerance) produces faceting that translates directly into profile error. Also check the ball end mill radius compensation (a poorly calibrated tool value shifts the entire surface systematically, not randomly) and edge wear in areas with long toolpaths.
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