Proposed in this paper is a new tool path generation method of 3-axis milling by using the guide surface, which is constructed with the machining region to be cut on the part surface. The guide surface, as an extension of the guide plane, globally takes the shape characteristic of the machining region into consideration well, and plays a key role as a domain space for planning the guide paths. Therefore, the proposed method can handle the region consisting of several trimmed surfaces just like the guide plane method. The final tool paths are calculated from the cutter contact-paths obtained by projecting the guide tool paths onto the machining region. Unevenly spaced tool paths, the major drawback of using conventional methods, can be also overcome by employing one of the projecting directions proposed. Tool path generation, an example of clean-up machining, is described for explaining the proposed method in detail. Some illustrative examples show the possibility that the method can be applied to the various 3-axis milling operations including high-speed machining. (C) 2000 Elsevier Science Ltd. All rights reserved.