GD&T Symbol Guide
Profile Of A Surface
Controls every point on a 3D surface within a boundary that follows the true surface profile.
Definition
Profile of a surface controls a full 3D surface so every measured point stays within a tolerance zone that mimics the nominal shape.
With datums, it can control form, orientation, location, and size relationships. Without datums, it behaves more like a form refinement.
Application
Use it for castings, molded parts, fillets, aerodynamic surfaces, complex contours, and model-based surfaces.
It is often the best choice when a surface is too complex for simple flatness, angularity, or position callouts.
Curved Casting Surface Controlled By Profile
Profile wraps the tolerance zone around the intended 3D surface instead of checking only a line section.
3D Tolerance Zone
Two equally disposed surfaces following the exact contour of the nominal profile.
Inspection Method
CMM scanning, laser scanning, or point-cloud comparison is common because the whole surface must be evaluated against the nominal model.
Simple radii or accessible contours may be checked with dedicated gages or traced measurements.
Worked Check: Molded Cover
A molded cover has surface profile 0.30 mm to datums A and B. Scan data shows the worst point is 0.12 mm outward and 0.09 mm inward from nominal.
Half-width
0.30 / 2 = 0.15 mm
A bilateral profile zone is commonly centered about the true profile.
Worst deviation
max(0.12, 0.09) = 0.12 mm
Both inward and outward deviations must remain inside the profile boundary.
Compare
0.12 <= 0.15
The scan stays inside the profile zone.
The surface passes. Profile gives one clean requirement for the full contour instead of many local dimensions.
Comparison Table
| Control | Coverage | Datum Use | Typical Measurement |
|---|---|---|---|
| Surface profile | Entire 3D surface | Optional | CMM or scan |
| Line profile | One cross-section | Optional | Trace or CMM |
| Flatness | One planar surface | No | Surface plate or CMM |
Notes
Profile of a surface is the 3D version of profile of a line.
A line profile may be used tighter than the surface profile to refine cross-section shape while keeping a broader whole-surface control.