In this paper is analised the dependence regression between flank wear tools or wear out of belt width on the back surface VB and cutting time t in the form of complex power-exponential regression equation for turning of cast iron GG-25 of cutting tools from nitride ceramic for the different values of the cutting speed v=60, 90 and 120 ?m/min?. Correlation coefficient for given examples of experimental researching is most R=0,998 and mean relative error of experiment is less α=1,25%.