where 𝐹𝐹 𝑓𝑓 is feed rate, S is spindle speed, 𝑝𝑝 0 , 𝑝𝑝 1 , 𝑝𝑝 2 , 𝑝𝑝 11 , 𝑝𝑝 22 and 𝑝𝑝 12 are the coefficients for the regression model and values are shown in Table . The R-Squared (R 2 ) values >0.85 suggest the satisfactory quality of regression models and the prediction accuracy will be further verified by experiment results in Section 5.