Limit gauges for checking smooth parts

The various functions performed in mechanical engineering (rotation, translation, immobilization, etc.) require the assembly of parts.

These assemblies have to comply with certain clearance or clamping characteristics that need to be mastered, and which derive from the actual dimensions of the assembled elements.

These dimensions therefore need to be controlled, and can be obtained by measuring with instruments such as calipers, micrometers, measuring machines, etc., or verified with specialized verifiers called "limit gauges", which materialize the acceptable dimensional and/or geometric limits of parts.

Limit gaging is a quick and easy method. It can also be more economical if the number of parts to be checked is large.

This article deals with this verification, firstly introducing the concepts of tolerance and fit necessary to define smooth parts (as opposed to threaded parts, for example) or the elements that make them up.

The interpretation of the dimensional limits of parts and the Taylor principle are discussed, then the main types of gauges used in industry and their essential characteristics are described.

Finally, the use of limit gauges, their conditions of use and verification are explained.