THROW-AWAY DRILL AND TIP ARRANGEMENT METHOD FOR THE DRILL

摘要

An object is to provide an indexable drill which has cutting edges formed of a plurality of indexable inserts and which provides stable performance so that the accuracy of entrance hole diameter and exit hole diameter is improved and generation of burrs at the hole exit can be suppressed. Indexable inserts 5-1 and 5-2 which form a center cutting edge 8 and a peripheral cutting edge 9 are attached to a drill main body 1 at an end thereof. A ratio between a cutting contribution A of the center cutting edge 8 and a cutting contribution B of the peripheral cutting edge 9 is set such that the cutting contribution A of the center cutting edge is larger. The indexable insert 5-2 is disposed so at to project forward in the axial direction from the indexable insert 5-1 so that an outer-end corner 9a of the peripheral cutting edge 9 engages a workpiece first.