During manufacturing process of mechanical parts, the method of material remove by cutting tools have a significant importance, according to the matter of the part manufacturing process and to its raw elaboration method. On one hand, the characteristics of machining operations depend on the “studies office” choices during the part conception (the shape, the material, ...). On the other hand, they also depend on the “methods office” choices (machining gamut, choice of: machines, tools, cutting parameters, and tools paths, ...). For the “methods office”, some bad choices of cutting forces could change the final quality of the machined part. In this order, we have studied the dynamic cutting law evaluation problem. This consists in developing a simplified phenomenological cutting force model, in a case of turning under orthogonal machining conditions in presence of vibrations.