4-1 TOLERANCING SYSTEMS

Manufacturing of parts cannot be absolutely precise. If such be the case, the cost of components would be horrendous. Already the differences in straightness or flatness, surface finish, the existence of tooling marks or tooling grooves, burrs, chips, and similar, can render the component unacceptable by too harsh a standard.

Yet, all these discrepancies can sometimes be present and for this reason designers and manufacturers devised a certain area of benevolent acceptance, called a tolerance range. This tolerance range specifies the amount of deviation a part can possess and still be acceptable and function well within an assembly.

Different manufacturing fields use a different tolerance ranges. Where 0.031 in. (0.79 mm) can be unacceptable in die work, the same tolerance range is too tight for, let us say, in steel constructions.

For comparison, quite precise tolerances for glass cutting are:

Minimal tolerances in woodworking, where NC equipment is utilized, are approximately:

Every manufacturing field adjusts the tolerance ranges to suit its needs. The fits, however, are a rather different story, as they always involve two parts, assembled together. Here the tolerance range must be somewhat standardized and often quite precise. After all, we are not fitting wooden shafts into openings drilled through glass.