An accuracy analysis of the peg-and-hole assembly problem

A peg-and-hole assembly may adopt clearance, transition or interference fits depending on the functional requirements of the particular design. The international standards that are used for the specification of the nature of a fit refer, nevertheless, only to dimensional deviations. They do not consider the actual geometry of the assembly components. Geometrical tolerances are assigned in addition to the dimensional tolerances whereas, for certain applications, the latter may also include some provision for them. Maximum and minimum functional clearances, dimensional and geometrical tolerances of a peg-and-hole assembly consist of a system where values of the first two variables are design-imposed and the dimensional/geometrical tolerance values have to be suitably allocated. This tolerance allocation cannot, however, be effected by a straightforward approach. The unknown variables are more than the available clearance/tolerance relationships and in the current engineering practice, the problem solution is usually based on experimental/empirical data and/or general tolerance assignment guidelines. The paper addresses this problem through a systematic analysis of the accuracy requirements of a peg-and-hole clearance fit assembly. The analysis is then followed by the development of a methodology for the evaluation of the dimensional and geometrical tolerances of the assembly components. The presented algorithm is further applied and discussed in a case study.