PURPOSE: To permit a plurality of primary and secondary angles to be readily ground by turning only a twist drill in setting grinding angles.

CONSTITUTION: In grinding the primary angle for forming narrow width cutting edges 1 and 2; a chuck head 10 is set so that the axis of a twist drill 15 is inclined to the horizontal direction from the center line of the grinder, and one narrow width cutting edge 1 is made to contact with the gage of the head 10 so as to be horizontal, and then the base holder is fed in parallel with the grinder to grind the narrow width cutting edge 1. Next, a lever 18 is drawn to move a rotary coupling 19 backward in order to disengage the clutch mechanism between it and a sleeve 20. Then turning the lever 18 permits only a holder 17 to turn 180 degrees, resulting in the other narrow width cutting edge 2 being parallel with the grinder to grind it similarly to the other.