Geometric Dimensioning and Tolerances

Geometric Dimensioning and Tolerances is a system with symbols used by engineers in design with the scope to define geometrical characteristics and its variation. Between the manufactured part and the CAD Design is always a difference due to the process variations. This is the way how the manufacturing and the design department communicate with each other about the possible accepted dimensional or positional tolerances.

The scheme above is a perfect example of why we should give great attention to geometrical tolerances. In this example, the ax rotating while the bearing moving back and forward on its surface. The friction-free motion between the two rotating elements exists if the centerline of each diameter of the ax coincides with datum line A.

There are four main types of geometrical tolerances:

  • Tolerance of form: Straightness, Flatness, Circularity, Cylindricity, Profile of line, Profile of surface;
  • Orientation tolerances: Parallelism, Perpendicularity, Angularity, Position;
  • Tolerances of location: Position, Concentricity, Coaxiality, Symmetry;
  • Runout tolerances: Radial circular runout, Axial circular runout, Total radial runout, Total axial runout.

Each category with explanation and example you can find in the next table.

The table with geometrical tolerances presented you can find right here:

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