A part definition drawing must accurately assume the functional requirements of the mechanical
system to which it belongs to enable correct functional dimensioning. This dimensioning is essential
for the methods office to define its production and for metrology to define its verification.
In this paper, we adopt a method that uses a 3D model of a mechanical system. It is therefore
necessary to provide the nominal models of the components. Also relies on analysing the
positioning of each part in the possible working states of the mechanical system.
The part functional dimensioning requires mastery of the ISO-GPS language (mainly UNE-EN ISO
1101:2017 and UNE-EN ISO 5459:2024) and a precise analysis of the operation and positioning of each
component.
Analysis of how the mechanism works must be based on the tolerance stackups, applying the ‘worst
case’ and statistical methods, depending on the number of components integrating the chain of
dimensions
The positioning of each part depends on the identification and definition of the contact surfaces
and on the order of the prevalence between them. This analysis of the part positioning will allow the
definition of the necessary datum systems and the definition of the initial GPS specifications of
dimension, tolerance zone and pattern (maximum or minimum material condition).
Both analyses should provide us with the ISO-GPS functional dimensions in the functional
definition drawings according to ISO 16792:2021 and other GPS standards.
