Abstract The scientific monograph deals with the optimization of geometry of the cutting edge in the machining of hardened materials in terms of durability of the cutting edge, its impact on the roughness of the machined surface of the work piece and the economic aspect in the selection of the inserts. The theoretical part is devoted to an overview of cutting materials and their impact on the state of the work piece machinability. The experimental part is evaluated impact of individual parts of cutting edge geometry on the roughness of machined surface and thus on the life of cutting edge from boron nitride. Key words: Geometry, cubic boron nitride, hard part turningweiterlesen