Abstract
Nicks engraved on the cutting edges of a twist drill split the chips into narrow bands which can easily flow out of the hole through the flutes of drill. As the result, the performance of the drill is improved considerably, especially when the depth of hole exceeds its diameter. Experiments in this paper show the effects of nicks such as lowered torque, smoother surface finish, diminished bur at the outlet of hole and the prolonged drill life : In a series of drilling test of φ 6 holes in 0. 45% C steel, nicks prolong the drill life up to ten times as long or even more. For the higher productivity, feed rate can be increased by about 30% without shortening drill life.
