Drill with groove width variation along the drill and double margin with a thinning section at the tip

Abstract

In a drill in which a chip discharge groove twisted in the shape of a spiral relative to an axis is formed in the outer periphery of the tip section of a roughly cylindrical drill body that rotates around the axis, and a cutting edge is formed on the intersecting ridgeline between a wall surface facing in the direction of drill rotation of this chip discharge groove and a tip flank of the drill body, together with the section on the tip side of the chip discharge groove continuous with the cutting edge being a narrowed width section in which the helix angle relative to the axis and groove width are constant, a wide width section is formed in the chip discharge groove farther towards the rear end than this narrow width section, in which the helix angle is equal to the narrow width section and in which the groove width is widened relative to the narrow width section in the direction of drill rotation and towards the rear in the direction of drill rotation and has a constant width.