Perturbation plot (Fig. 13) indicates the increasing trend of the surface roughness with an increasing value of feed rate which is maximum at coded value of 1, whereas with an increase in cutting speed, surface roughness decreases, which is minimum at coded value of 1, and with an increase in depth of cut, surface roughness shows fluctuating behavior ; it first increases and then decreases. Therefore, feed rate is the most significant factor which changes the value of surface roughness.