Indexable drill insert and rotary cutting tool employing same

A drill comprising:

• a drill body disposed about a longitudinal axis, the drill body having a first end and an opposite second end, the first end being adapted to be disposed in a machine tool and the opposite second end having a first pocket formed therein generally at or about the longitudinal axis;
• and
• an indexable insert disposed in the first pocket, the indexable insert comprising:
• a top surface;
• a bottom surface;
• a side surface extending between the top and bottom surfaces from multiple sides of the insert;
• a central mounting aperture extending between the top surface and the bottom surface;
• and
• a plurality of identical cutting edges disposed at the intersection of the top surface and the side surface, each cutting edge comprising:
• a first part edge disposed tangent to a first reference circle aligned about the central mounting aperture;
• a second part edge extending from the first part edge, the second part edge being connected to the first part edge via a convex curved portion;
• a third part edge disposed tangent to a second reference circle aligned about the central mounting aperture, the second reference circle having a smaller diameter than the first reference circle, the third part edge being connected to the second part edge via a concave curved portion;
• and
• a convexly curved corner portion extending from the third part edge of one of the identical cutting edges to the first part edge of another one of the identical cutting edges,
• wherein the insert is a quadrangular indexable insert and the plurality of identical cutting edges comprises four cutting edges;
• wherein the convex curved portion of the insert is the axially fowardmost portion of the drill;
• and
• wherein the first part edge of the insert is disposed at an angle in the range of about 50° to about 90° with respect to the longitudinal axis.