Abstract: Tolerance is used to give the variational extremum for the real parts and the information can now be added to the parts as text attributes in three demesional CAD systems. But how to interpret the information and generate the variational geometry for the parts is still a difficult task. How to generate the variational geometry for the holes is systematically analyzed. At first all possible combinations of tolerance specifications for holes are given. An efficient method for determining the variational boundary for the hole axis is proposed based on the given tolerance requirement. A mathematical model for the generation of variational geometry of the holes is systematically deduced and the realization approach is developed based on the geometric modeling kernel-ACIS. An example is given to illustrate the proposed model.

Key words: CAD/CAM, Holefe ature, Tolerance, Variational geometry