Tolerance design of datum systems

A majority of mechanical products and devices can be viewed as a collection of parts engineered to assemble so that mating parts and features satisfy some predetermined spatial relationships. Designers typically satisfy the constraints that arise from these relationships by using a set of specific physical features to create on each mating part an accurate reference frame from which all other relevant geometric elements are located. The accuracy and precision with which two mating parts assemble and influence subsequent alignment of other features are controlled by the nominal dimensioning and tolerancing scheme imposed on the geometric elements used to create the two coincident reference frames. The paper presents the development and implementation of a computer aid to assist designers in the allocation of design sizes and tolerances that satisfy functional translation, rotation and assembly constraints imposed on four datum systems commonly used in design.