Tolerancing

From FreeCAD Documentation
Revision as of 05:38, 23 September 2020 by Vanuan (talk | contribs)

Tolerancing, Geometric dimensioning and tolerancing (GD&T) means specification of permissible limits/deviation of dimensions. Here we're talking strictly about geometric tolerances: a real-world error of shape, size, location, orientation in a relation to the designed ideal.

There's also a distinction between the terms "limits and fits" and "geometric tolerances and surface conditions".

Standards

There are 2 ANSI/ISO standards:

  • ISO 1101 / ASME Y14.5 Stating and interpreting Geometric Dimensions and Tolerances (Definitions and symbols)
  • ISO 16792 / ASME Y14.41 Model-based definitions (CAD data) 3D model presentation and geometric dimensioning and tolerancing

There's also ISO 10303 (informally "STEP") which defines the file format for exchanging product and manufacturing information which is sourced from model-based definitions.

So there are 2 approaches here:

  • The legacy approach of producing 2D drawings with GD&T symbols
  • The modern 3D approach which embeds GD&T data into the model and produces drawings with GD&T symbols

Existing software

Implementation so far

Forum threads

Tutorials and learning materials on GD&T