The manufacturers search always a good compromise between the quality of machined parts and the machining time in order to reduce the costs, which is the principal preoccupation of the NC part programmer. Therefore, a methodology permitting a better approximation of the surface and a good choice of the machining strategy and its different parameters in particular the optimum tools becomes necessary. Currently, several approaches are developed to optimize machining times for finishing free form surfaces on CNC milling machines. Some of these methods consider only the cutting conditions of machining, others the optimal machining strategy and others the selection of the optimum tools. In this paper, a methodology is proposed for finishing free form surfaces on 03-axes CNC milling machines by considering the local shapes of the surfaces, the choice of machining strategies and the optimum ball end mill tools. This methodology is more effective when using machining centers.