Computer-Aided Tolerance Charting for Products with Angular Features

This paper describes a process by which computer-aided design methods are used for the tolerance charting of products with angular features. If a product contains one or more angular features, such as chamfers and tapered surfaces, radial or normal machining of the features will result in axial dimension changes. In this paper, basic trigonometric formulae are first presented to explain the phenomenon of tolerance accumulation. In the process of tolerance charting, dummy cuts are included to reflect the corresponding dimensional changes due to indirect machining. With the assistance of flags and linked lists, the system proposed can automatically identify all dimensional chains which are associated with either regular cuts or dummy cuts. Moreover, optimisation techniques are recommended to allocate the allowable tolerances as specified by blueprints. In the search for an optimal design, the total manufacturing cost defined by the working tolerances is the objective function to be minimised.