The present invention provides a drill comprising: a drill main body rotatable
about an axis of rotation, and having a tip end with a tip flank and a shank; a
chip discharge flute formed on a periphery of the drill main body, and extending
from the tip end toward the shank of the drill main body; and a cutting edge formed
along an intersecting ridge where a wall surface of the chip discharge flute facing
in the direction of drill rotation intersects the tip flank of the drill main body,
wherein the cutting edge comprises a convex cutting edge toward the periphery and
a concave cutting edge smoothly extending from the convex cutting edge. When drilling
work is performed with this drill, the chips are generally curled and can be smoothly
discharged without being excessively abutted against the wall surface of the chip
discharge flute; consequently, the chips can be smoothly discharged, and the drill
main body is subjected to less frictional resistance, which leads to less wear
on the drill and less driving torque for drilling. Therefore, the drill life can
be preferably extended even under severe drilling conditions, such as during high
speed drilling, and smooth and stable drilling can be performed.
