Method of boring long holes - uses offset internal pilot hole to reduce formation of long metal chips

摘要

Method of preventing the formation of excessively long chips when boring deep holes in ductile materials. The formation of such chips can damage the boring tool or the surface of the bored hole. This is prevented by boring a pilot hole of a considerably smaller diameter than the main hole. The pilot and main holes are either tangential internally with respect to the main hole, or intersect so that after completion of the main hole there exists a groove of crescent shaped section. The length of chips formed when the main hole is drilled are limited to that of the material removed by one turn of the drill.