Geometric Tolerances Orientation Profile Any Surface
The profile of a surface is an orientation tolerance that defines the allowable three-dimensional deviation of an entire surface from its designed ideal shape. It expands the idea of a profile line from a single cross-sectional line to the entire surface. Surface profile is especially important when a part has complex shapes, curves, or freeform surfaces where accuracy cannot be controlled by individual dimensions alone.
The tolerance zone is formed between two boundaries that resemble the designed surface. The distance between these boundaries is the tolerance value indicated on the drawing. All points on the actual surface must lie within this zone. According to the ISO 1101 standard, the surface profile is defined as one of the key profile tolerances.
Applications
- Casting and plastic parts: control the accuracy of complex shapes cost-effectively.
- Aerodynamic and hydrodynamic surfaces: ensure that surfaces affecting air and fluid flow remain sufficiently accurate.
- Sealing surfaces: prevent leaks and ensure compatibility of parts.
Notation on drawings
The surface profile is indicated using a geometric tolerance frame with the profile symbol ∩ and the specified tolerance value, for example:
| ∩ | 0.3 | A |
This means that every point on the actual surface can deviate no more than 0.3 mm from the designed shape within the defined tolerance zone relative to datum A.
Significance in manufacturing
The surface profile tolerance is an effective tool because it allows control of the entire surface's accuracy with a single notation. If the surface profile deviates too much, parts may not fit together, resulting in gaps, leaks, or reduced performance—for example, in fluid dynamics. Conversely, if the tolerance is too tight, manufacturing costs increase, as it requires fine machining and measurement, often using a coordinate measuring machine (CMM).
The surface profile tolerance gives the designer the ability to ensure both the functionality and appearance of a part without making manufacturing unnecessarily expensive.
