Tolerance is almost ubiquitous during the whole product lift cycle and is imperative for seamless integration of CAD and CAM. Based on the mathematical definition of tolerance, a 3D tolerancing system, 3DTS, is presented with its design prin- ciple, system architecture and key functions. The following functional modules, tolerance modeling, semantics interpretation, 3D tolerance analysis, are described in detail. To make the tolerancing system robust and efficient, many techniques such as hierar- chical tolerance representation, rule-based evaluation and non-intersection determination of tolerance zone have been devised. Tested by many samples, this system shows good robustness and practicability.
