Rapid prototyping plays an important role in product development. There are two ways to realise rapid prototyping: one is to develop new prototyping equipment such as stereolithography apparatus (SLA), selective laser sintering (SLS), etc., and the other is to improve existing CNC techniques. In this work, a robot system for rapid prototyping, which is an enhancement of the CNC based method, is presented. A robot arm holding a milling tool is used to machine the prototype of a solid model drawn using a commercial CAD system. In this paper, Part 1, a strategy using the robot for rough machining is discussed and then an automatic tool-path generation method using a grid height array is presented. This method can generate tool paths for rough machining with different tolerances. As a verification of the proposed algorithm, a number of prototypes have been produced, which have demonstrated the feasibility and advantages of the algorithm. In a companion paper, Part 2, an approach to represent C-space by incorporating possible variations in tooling orientations is proposed. In order to reduce error on complex surfaces resulting from undercut or overcut operations, a curvature-matching algorithm is developed. Finally, experimental work using the collision-free planning strategy and simulation for the curvature matching algorithm is carried out.