(5) When finish cutting of hardened steel, the thrust forcebecame the largest among the three cutting force components and was the most sensitive to the changes of machining parameters.(6) Simultaneous optimization of the performance characteristics (tool life, surface roughness and cutting forces)when hard turning of AISI 52100 bearing steel with CBNtool was achieved with a cutting speed Vc = 168 m/min,feed rate f = 0.08 mm/rev and depth of cut ap = 0.22 mm.(7) The proposed experimental and statistical approachesbring a reliable methodology to optimize and to improve thehard turning process. Also, they can be extended efficientlyto study other machining processes.