Patent ID: 7182556

Claim:
A drill having an axis comprising: a drill main body being rotatable about the axis including: a distal end face formed in an isosceles triangle shape; a concave groove which opens to the distal end face and forms a plate-shape space along the axis; and a plurality of guiding grooves provided on an inner surface of the concave groove, and extending in a direction of the axis; and a throwaway insert formed in a plate-shape and detachably attached to the plate-shape space of the drill main body including: a plurality of convex portions provided on an outer surface of the throwaway insert, which are formed such that each of ridges thereof extends in the direction of the axis, arranged side by side in a direction crossing the axis, and engageable with the guiding grooves; and tapered portions, each of which is connected to each proximal end of the convex portions, and inclined so that a height thereof with respect to an outer surface of the throwaway insert is lowered toward a proximal end of the throwaway insert along the direction of the axis, wherein distal ends of the guiding grooves and the tapered portions are arranged following the isosceles triangle shape of the distal end face of the drill main body, and the throwaway insert is attached to the drill main body by being inserted into the concave groove along the axis from the distal end face to the concave groove while engaging the convex portions with the guiding grooves.