Boring bit with two cutting edges - has non-symmetrical form so that unused cutting edge is not damaged during cutting with other edge

摘要

The boring bit for a drill is made in the shape of an irregular hexagon, with two opposite cutting edges (3', 6') and two non cutting edges (4, 5). The bit is so made that the distance (B) across the cutting edges is slightly greater than the distance (A) across the non-cutting edges. This enables one cutting edge to be used until it is worn and then by rotating the bit about the axis of the hole (21) the opposite edge can be used. At the same time the position of the hole ensures that the unused cutting edge is not damaged before it is brought into use.