There are two dimensional sets in a tolerance chart: the blueprint (B/P) dimensional and the working dimensional group. The interrelation between these dimensional groups makes it very difficult to assign appropriate tolerances to individual working dimensions. This paper deals with the automatic tolerance assignment problem in a tolerance chart, especially for computer-aided tolerance charting. lifter the manual methods of tolerance assignment are briefly discussed, a linear programming model is analysed. Owing to the impractical solution from the linear programming (LP) model, a proportional smoothing approach is described with a numerical example, which can assign appropriate tolerances automatically and systematically, based on the requirements of both blueprint dimensions and process capabilities. The result from this approach is compared with that of the LP model and the original manual procedure. Finally, the approach is extended to a statistical tolerance model.
