Flatness is a form tolerance in GD&T that controls how much a surface can deviate from being perfectly flat. It ensures that the surface does not have excessive waviness, warping, or unevenness, which is critical in applications where a component must mate properly with another part.
Symbol for Flatness
- Flatness Symbol: ▱ (parallelogram)
Flatness Tolerance Zone
- The tolerance zone consists of two parallel planes separated by the specified tolerance value.
- The entire surface must lie within these two planes.
Comparison with Other Form Tolerances
- Flatness vs. Straightness:
- Flatness (▱) applies to an entire surface.
- Straightness (⏤) applies to a single line element in a single direction on a surface.
- Flatness vs. Parallelism:
- Flatness controls only a single surface’s form.
- Parallelism controls the orientation of one surface relative to another.
- Flatness vs. Profile:
- Flatness keeps a surface within two parallel planes.
- Profile of a surface allows for more complex contours to be controlled.