Horse Power Calculator for Spade Drill

From the McGraw-Hill Machining and Metalworking Handbook 3rd Edition -

APPROXIMATION:

C_hp = P(F)(N){πD²/4}

T_p = 148,500(P)(F)(D)

M_hp = C_hp/e

F = f_m/N

Where:

C_hp = horsepower at the cutter

M_hp = required motor horsepower

T_p = thrust for spade drilling, pounds force

D = drill diameter, in

F = feed, ipr (in your case use 0.022)

P = power factor constant (in your case use 0.75 or 1.0 with dull tools)

f_m = feed, ipm

N = spindle speed, rpm

e = drive motor efficiency factor (0.90 for direct belt drive to the spindle; 0.80 for geared head drive to the spindle)

Quick check of understanding:

In the formula does the small "n" represent nominal diameter?

Ask the vendor or contact the manufacturer of the cutting tool. They should be able to send you a spec sheet of recommended RPM's and required power ratings. Typically these sheets will cover several types of materials. Pick the one closest to what you will be machining as a starting point.