Geometrical Specification for Non-rigid Parts

In the absence of other indications, all the specified dimensions and tolerances are applied and controlled without the action of any force, except gravity, but components such as thin metal and flexible parts, rubber gaskets, and flexible parts in general, can deform or bend, even as just a result of their weight. These components should be inspected under a restrained condition in order to simulate their shape in the installed condition. The restraint or force on the non-rigid parts is usually applied in such a manner as to resemble or approximate the functional or mating requirements. According to the ISO standards, the non-rigid partsNon-rigid parts should be identified on a drawing by means of “ISO 10579-NRISO 10579-NR” (Non Rigid) obligatory indications within or near the title block; such a note indicates that the part is not considered rigid and it indicates the clamping forces or other requirements necessary to simulate the assembly conditions. In order to invoke a restrained condition in the ASME standards, a general note, or a local note, should be specified or referenced on the drawing to define the restraint requirements. When a general note invokes a restrained condition, all the dimensions and tolerances apply in the restrained condition, unless they are overridden by a “free state” Ⓕ symbol.