Abstract: A twist drill is disclosed. The twist drill comprises a substantially cylindrical tool body having a rotational axis therethrough, a front portion, a rear portion, a plurality of web thickness, a front flank face, a plurality of flutes formed on an outer peripheral surface thereof and extending to the front flank face, and a land disposed between a pair of the flutes. The flute has a wall portion facing toward the rotational direction of the tool body. A cutting edge is formed at an intersection between the wall portion of the flute and the front flank face. The web thickness at the rear portion of the tool body is smaller than the web thickness at the front portion of the tool body.

Abstract: A high performance drill bit is presented for precision drilling of holes in hard-to-drill materials, such as a carbon fiber reinforced plastic material. The drill is a gun drill type having a pair of flat flutes and a pair of air holes for delivering coolant and/or lubricant. The main feature of the drill is the provision of two pairs of cutting edges formed on the intersecting ridges formed at the leading sides of the flank surfaces with the flute surfaces. At the tip of the drill bit, a pair of primary cutting edges, having a point angle .alpha., is disposed. It is followed by another pair of secondary cutting edges, having a point angle .beta., where .alpha.>.beta.. Physically, this means that the secondary cutting edges are inclined more toward the drill axis than the primary cutting edges. The secondary cutting edge is followed further by another flank surfaces which are even more inclined toward the drill axis.