GOM Metrology

GOM Metrology

White Paper

Geometric Dimensioning and Tolerancing (GD&T)

# White Paper: Geometric Dimensioning and Tolerancing (GD&T)

## Increase Quality and Reduce Costs

Today's modern manufacturing machinery can achieve very high degrees of accuracy. Nevertheless, workpieces continue to suffer from undesired deviations in their nominal dimensions and geometries. To limit the resulting quality losses and cost increases, manufacturers and metrologists rely on tolerances. Tolerances define what deviations from the nominal value are acceptable—and when a part is considered “not OK” (NOK) and thus unusable without improvement.

When tolerancing parts, Geometric Dimensioning and Tolerancing (GD&T) plays an important role. GD&T describes the type and form of permitted geometric deviations in the part with extreme accuracy. Compared to conventional tolerancing, a product specification that uses GD&T has several advantages:

• Simplified manufacturing and component testing
• Optimal comparability
• Option to combine tolerances
• More usable tolerance in round and cylindrical elements
• No tolerance aggregation through chain dimensioning
• Suitable for complex, freeform parts
• Component testing with product and manufacturing information (PMI/FTA) support

### GD&T Representation

An international language of symbols has been developed to represent GD&T in drawings. We have compiled these in clear posters.

In our white paper you will learn more about the advantages of form and position tolerances and receive extensive application and practical examples. Our posters give you a good overview of the visual representation of tolerances.

## GD&T Interpretation

Both GD&T and the measuring results of the tolerance check are expressed as pure numerical values. However, interpreting these numbers and translating them into specific corrective actions is a challenge. GD&T is most easily inspected using software that color-codes nominal and actual values and uses vectors to represent deviations.

### GD&T Standards

The rules, symbols, definitions, requirements, default values and recommended methods for determining and interpreting GD&T are established in systems of standards, although only two see global acceptance and use:

ISO GPS (geometric product specification), established by the International Organization for Standardization

ASME Y14.5, established by the American Society of Mechanical Engineers