The needs of today's complex manufacturing systems requires the use of machine tools operated by means of an adaptively controlled system. Adaptive control provides continuous monitoring of performance and adjusts the system variables in order to approach the conditions optimum for the chosen performance objectives. This investigation proposes the in-process parameter estimation method of tool life in turning, in which the force ratio of feed force to tangential force due to the tool wear is detected. The method involves the analysis of the optimum cutting conditions based on the machining cost per unit volume of metal removed under the considered cutting constraints.