Abstract: Different types of tolerance are defined for different functional and manufacturing requirements and each type of tolerance is represented in a way suitable for it to fully take advantage of a computer implementation of tolerance. A hierarchical tolerance representation model is proposed in our study. The model is divided into three tiers the tier of the topologically and technologically related surfaces(FTTRS), the tier of the minimum feature datum elements(MFDE) and the tier of constraint primitive(CP). The relationship between them is also studied and defined. After this, the realization of the model is given. Using this tolerance, the seamless integration of tolerance information in CAD system is realized.

Key words: CAD/CAM, Tolerance Representation model Feature, Knowledge reuse, Machining intent, Process knowledge, Similarity measurement