Meaning
International standards define the rules for establishing and applying datums in technical product documentation and metrological verification. Adhering to ISO 5459 ensures that the references used for measuring a plastic part are consistent across different inspection sites. This document specifies the symbols and terminology for datum features and datum systems.
Datum Definition
Theoretical axes and planes are derived from the physical surfaces of a part to create a stable reference for dimensional checks. Compliance with ISO 5459 requires the inspector to identify the primary, secondary, tertiary and auxiliary features that lock the part in three-dimensional space. These rules apply regardless of whether the measurement occurs on a manual jig or via a laser scanner.
Measurement Consistency
Discrepancies between the toolmaker report and the moulder inspection often stem from different interpretations of the datum structure. Standardized application of ISO 5459 eliminates this ambiguity by providing a universal language for geometric dimensioning and tolerancing. Precise datum selection is especially vital for flexible polymer parts that might deform under their own weight.
Specification Linkage
Designers use these guidelines to communicate which surfaces must be held to the tightest tolerances. This clarity ensures that the functional requirements of the assembly are met without over-specifying the part. Standardized datums also allow for the automated inspection of parts across global supply chains.
