Third Step:

On putting the values of T₁ and T₂ in Eq. (8), we get

750 = B /(78.889)^1/n                                        . . . (E1)

11.2 = B/(128.07)^1/n                                                  . . . (E2)

Divide first one (E1) by second (E2),

or, (1.62)^{1/ n} = 66.845

∴ 1/ n  = 8.71

From Eq. (E1),

B = 2.53 × 1019

Putting these values in Eq. (12), we get,

= 2.05 × 10¹⁷

V_opt = 97.18 m/min

After having obtained the optimum cutting speed, the corresponding spindle speed

(N₃)  can be obtained as follows :

N₃  = V_opt / π = 97.18/ π × 0.0762

N₃ = 405.95

∴ N₃ = 406