3 June 2015: Gunter Effenberger

Hardly any drawing does not refer to the tolerance classes of the ISO 2768 standard for general tolerances. However, I have recently received many queries about how these “old“ standards (ISO edition issued in 1989) agree with current general standards of the GPS system. This article answers this and many more questions relating to general tolerances.

Meaning of general tolerances

On the one hand, the eleventh principle or functional control principle of the basic standard ISO 8015 demands

“that the specification of a workpiece is complete when all intended functions of the workpiece are described and controlled with GPS specifications."

This is the reason why any functional geometrical characteristic is defined separately by means of the symbols and tolerances the GPS system provides. On the other hand, the third principle or definitive drawing principle says that

“all specifications shall be indicated on the drawing using GPS symbology. Consequently, requirements not specified on the drawing cannot be enforced. “

Interpreting this principle, this means that drawings must be subject to complete dimensioning and tolerancing to communicate all specifications with supplier (manufacturer) and customer (recipient). General tolerances close the gap between concrete tolerancing of single characteristics (ensuring functional control) and the tolerancing of all characteristics (ensuring completeness in consideration of economic producibility).

Declaring tolerance classes based on general tolerance standards, you may supply any geometrical characteristic with tolerances. Since general tolerances have been developed or defined for specific production techniques, they weigh and agree on an economic production ”along the way“.

How these standards align with the GPS system

Standards on general tolerances are at the lowest level in the GPS hierarchy. They are referred to as complementary or supplementary standards. Their definitions thus supplement the information given in the basic GPS standards and all the other standards relating to geometric elements such as size, form, location, run-out, roughness and edges of bodies. The rules and principles of superior standards always apply unless a general tolerance standard suspends them...