The aim of this research is to investigate the effects of process parameters (cutting speed, feed rate and depth of cut) on performance characteristics in finish hard turning of AISI 4340 steel.The effect of machining parameters has long been an issue in understanding mechanics of turning. Machining parameters has significant influence on chip formation, heat generation, tool wear, surface finish and surface integrity during turning Therefore, an effort has been made in this research to evaluate the effect of machining parameters on surface roughness when turning with CBN tool. Machining trials are performed based on full factorial design under dry condition. The combined effects of the process parameters on performance characteristics are investigated using ANOVA analysis.Taguchi methodology is used to find out the optimal cutting parameters in hard turning. The orthogonal array, the signal- to-noise ratio, and analysis of variance (ANOVA) are employed to study the performance characteristics in turning operation of AISI 4340 steel bar.