What is ISO 21204 about?
ISO 21204 defines a number of specification operators for the specification of extended edge transition features between features. An edge transition feature is an integral feature connecting two adjacent integral features. The extended edge transition feature includes portions of the adjacent features. All these specifications apply to any line in a defined direction in the extended edge transition feature. ISO 21204 also defines the specification modifiers and the drawing indications for such transition specifications.
The proportions and dimensions of the graphical symbols to be used are also specified. The specifications defined in this document are suitable for relatively simple edge transition functions, for example ensuring assembly without interference. For more complex functions, geometrical tolerancing offers more precise tools. ISO 21204 is by intention limited to only edge transition features between two planes and between a cylinder and a plane nominally perpendicular to it. ISO 21204 provides a set of tools to express several transition specifications.
NOTE 1: ISO 21204 does not present any information on the relationship between a function or a use and a transition specification.
NOTE 2: Corners (the transition between three or more features) are not edge transition features and are consequently not covered by ISO 21204.
Who is ISO 21204 for?
ISO 21204 on transition specification is beneficial for:
- Programmers
- 3D Viewers
- Transition planning and support team
Why should you use ISO 21204?
ISO 21204 is a geometrical product specification (GPS) standard and is to be regarded as a general GPS standard.
ISO 21204 influences chain-link A, B and C of the chains of standards on form, orientation, and location. Most specification illustrations in ISO 21204 show edges drawn as sharp corners. They equally have been drawn showing the nominal geometry of the transition feature, without changing the meaning of the indications. In a computer aided design (CAD) system, the transition feature geometry can be modelled or not without changing the meaning of the indications. All the specification illustrations in ISO 21204 show a 90° angle between the two adjacent features. Specifications according to ISO 21204 have the same meaning, taking the nominal angle into account, regardless of the angle between the two adjacent features. All figures in ISO 21204 have been drawn with dimensions and tolerances in millimetres. It is understood that other units of measurement have been used equally well without prejudice to the principles established. ISO 21204 provides a set of tools for indicating transition specifications.
Overall, ISO 21204 is helpful as it provides an edge transition feature. Specifications for edge transition features according to ISO 21204 specify either extended edge transition sections defined in a specified set of intersection planes, where the specification for each section is independent of the other sections, or collections of such sections, for example a requirement
that the radius shall be consistent along the edge transition feature.
