Patent ID: 8393831

Claim:
A drill body of an indexable drill comprising: an insert attachment seat on which a cutting insert formed on a leading end side of the drill body in a direction of an axis of rotation is removably installed; and a chip discharging groove formed so as to extend from a leading end surface to a trailing end side of the drill body in the direction of the axis of rotation and through which chips generated by the cutting insert are discharged, wherein a wall surface defining the chip discharging groove is defined by a first wall surface facing in a drill rotating direction and a second wall surface crossing the first wall surface, the insert attachment seat comprises a central edge attachment seat on which the cutting insert is installed close to an axis of rotation and an outer peripheral edge attachment seat on which the cutting insert is installed away from the axis of rotation, the wall surface of the chip discharging groove is partly formed on a thinned wall portion thinned by the central edge attachment seat and the outer peripheral edge attachment seat, a crossing portion between the first wall surface and the second wall surface in the thinned wall portion is rounded, the drill body is formed of one of materials including carbon steel, alloy steel, and tool steel, and having a hardness of at least 40 HRC and at most 60 HRC in terms of Rockwell hardness, per JIS Z 2245:2005, and at least a portion of the wall surface of the chip discharging groove comprises a milled surface having a surface roughness of greater than 0.1 μm and at most 0.5 μm in terms of arithmetic average roughness Ra, per JIS B 0601:2001.