Indexable drill and method for arranging inserts in the drill
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 which form a center cutting edge and a peripheral cutting edge are attached to a drill main body at an end thereof. A ratio between a cutting contribution of the center cutting edge and a cutting contribution of the peripheral cutting edge is set such that the cutting contribution of the center cutting edge is larger. The indexable insert is disposed so at to project forward in the axial direction from the indexable insert so that an outer-end corner of the peripheral cutting edge engages a workpiece first.
1. A method for arranging inserts in an indexable drill, comprising the steps of:
arranging a first indexable insert and a second indexable insert at an end of a drill main body at positions where distances from a rotational center (O) differ from each other and which are separated from each other by half turn in the circumferential direction of the drill;
positioning the second indexable insert at an outer side of the drill so as to project forward in an axial direction from the first indexable insert at an inner side of the drill, so that an outer-end corner of the second indexable insert engages a workpiece first, and setting a ratio between a cutting contribution (A) of a center cutting edge formed of the first indexable insert and a cutting contribution (B) of a peripheral cutting edge formed of the second indexable insert in the range of A:B=52:48 to 55:45; and
arranging the first and second indexable inserts at positions where the ratio between the cutting contributions of the center cutting edge and the peripheral cutting edge is maintained within the range of A:B=52:48 to 55:45 by changing the positions where both the peripheral cutting edge and the center cutting edge are fixed when an outer diameter of the indexable drill is changed.
2. The method for arranging inserts in an indexable drill according to claim 1 , wherein the two indexable inserts used before the drill diameter changed are attached to a drill main body which is changed the drill diameter.