Machining time for turning operation:

Machining time for turning operation under the specified cutting conditions might be determined as follows. In turning, suppose t_m is the machining time, l is the length to be turned, L is the total tool travel in the feed direction, f_r is the feed rate per revolution and N is the rotational speed. After that, the relationships might be expressed as

                                                        ----------- (4(a))

                                                          L = l + y + Δ     .------------- (4(b))

here, y refer tool approach, Δ refer over travel, if any, and p_n is number of passes. p_n based upon the machining allowance, A_m (or the thickness of the material to be machined). Typically, in the last pass (or finishing pass) the depth of cut (d) is smaller than the roughing pass. But, if it is similar for all passes (Figure 5(b)) after that

                                          p_n = A_m / d                ----------- (4(c))

Hence, total machining time might be evaluated from

     -------------- (4(d))

If finish machining allowance is to be let separately, after that number of passes might be evaluated from the equation that following :

                                                  .---------- (4(e))

Here, A_f is finishing allowance, & d_f is depth of cut in final pass. Last value of p_n must always be an integer number. Therefore, it is evident from Equation (4(d)) that by decreasing y, and A_m, or by enhancing d, f_r and N, the total machining time might be decreased or the productivity might be increased.