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Flatness

  • Form Tolerance

Key Points

  • Flatness is the condition of a surface having all elements in one plane.
  • A flatness tolerance specifies a tolerance zone defined by two parallel planes within which the surface must lie.
  • Flatness is a form tolerance. Datum feature references are not allowed.

Example Drawing

Application

How to Read It

1

0.6 Profile tol zone

2

0.1 Flatness tol zone (A)

The surface must lie between two parallel planes 0.1 apart. The tolerance zone is unrelated to the datum or basic dimension. The flatness zone may “float” inside the profile zone.

3

0.1 Flatness tol zone (B)

Since the datum is a plane on the high points, the flatness tolerance zone is all to the inside.

4

Datum A contacting high points

5

Flatness is a 3D tolerance

The 0.1 Flatness tol zone is between two parallel planes in 3D space.

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