Force and Torque:

Throughout drilling, the drill is subjected to a axial thrust (T) and twisting couple (M). The values of T and M are governed by workpiece properties (strength, hardness), along the drill geometry (helix angle, diameter, chisel angle, point angle and number of cutting edges) and cutting conditions (depth of cut, feed rate, and cutting fluid).

The torque acting on the drill is attained from an empirical relationship as following:

M = C₁ D ^1.9 f ^0.8     kg-mm

Here, C₁ is a constant whose value based on the cutting conditions and workpiece material, D is drill diameter and f_r is feed rate in mm/rev.

The thrust force (T) acting on the drill is evaluated by using the empirical relationship:

T = C₂ D f ^0.7

Here, C₂ is another constant whose value based on the cutting conditions and workpiece material.

In drilling Power needed, can be calculated if specific energy (U) needed for drilling one unit volume (MRR) of work piece material is known. I

Power = U 8 MRR

Here, MRR is the material eliminated per unit time (= (P D² f_r N) / 4) here, f_r is feed rate per revolution, D is drill diameter and N is spindle speed in RPM).

Power is also defined as

Power = Torque ´  Rotational speed in radians/seconds.

                                          =  M  (P * N_s)   

Here, N_s is revolution per second of the drill.