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Form and Position Tolerances

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Definition: Form and position tolerances are geometric tolerances used to limit the permissible deviations from the ideal forms and positions of a workpiece. They are part of the Geometrical Product Specification (GPS) and are governed by DIN EN ISO 1101. They supplement dimensional tolerances with functionally relevant geometric requirements.

Practical relevance: Form tolerances concern, for example, flatness, roundness or cylindricity, while position tolerances cover, among others, parallelism, perpendicularity or position. The assessment is carried out by comparison with defined tolerance zones. Incorrect tolerancing can lead to assembly problems, increased wear or malfunctions. Drawing entries must contain clearly referenced datum elements.

Decision-making perspectives:

  • Technical decision-makers: Function-oriented tolerance definition taking into account manufacturability and costs.
  • Purchasing/project management: Clear specifications to avoid scope for interpretation by suppliers.
  • Science: Analysis of tolerance chains, measurement uncertainties and manufacturing variations.
  • Insurance/law: Clear basis for assessing complaints and dimensional deviations.

Typical testing or verification methods: Coordinate measuring machine (CMM), roundness measurement, optical 3D measuring systems, evaluation in accordance with the GPS standards.

FAQ:

  • Why are form and position tolerances more important than dimensional tolerances alone?
  • They ensure that components fit together functionally, even when dimensions lie within the dimensional tolerance.
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