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.
A drill which includes a cylindrical main body and a shank contiguous to each other, and which is to be rotated about an axis of the cylindrical main body in a predetermined rotating direction, for enlarging a hole previously formed in a workpiece through a die-casting process. The cylindrical main body has flutes which are formed in the cylindrical mainbody and extend from an axially distal end portion of the cylindrical main body toward the shank, so as to provide cutting edges in the axially distal end portion of the cylindrical main body. The cutting edges cooperate with each other to define a point angle which is larger than 170.degree. and is smaller than 180.degree.. Each of the cutting edges is substantially straight or is curved to be convexed as seen in the direction perpendicular to the axis.
The present invention relates to a V-notched web formed on a drill insert of a drill tool assembly. The V-notched web allows greater stability and feed rates, while decreasing the heat generated at the insert tip. The present invention is provided by a drill insert comprising a drill insert body having at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle.
