Drilling and Tapping

Abstract

A two flute twist drill manufactured from high speed steel is used almost universally for producing round holes in most known materials. The drill is used to produce the initial hole, but as the drill is removing solid metal equal to the drill diameter and is subjected to high torque and thrust loads, the hole produced is not very accurate in size, has a varying roughish finish and its position depends on such factors as whether drill bushes have been used or whether the hole has been previously centre-drilled, or merely centre-popped.