DRILL Russian patent published in 2009 - IPC B23B51/00 B28D1/14 

FIELD: mechanics.

SUBSTANCE: drill includes spike with multiple cutting blades oriented outwards. Each cutting blade includes cutting edge formed by junction edge line between cutting surface and facet, and section formed by interconnection of radial internal ends of cutting edges in the central part of spike when viewed from below. At least one cutting blade of the drill has first facet at the end section of its external periphery and second facet at the lateral section of its internal periphery. First facet features a facet at the blade point side close to cutting edge and a facet at the side of base formed at facet base surface at the blade point side, so that inclination angle of the facet at blade point side tilted in axial direction is less than inclination angle of the facet at base side tilted in axial direction, and so that inclination angle of the second facet tilted in axial direction is more than both inclination angle of the facet at blade point side and inclination angle of the facet at base side.

EFFECT: improved performance due to reduced crumbling of external blade ends.

9 cl, 14 dwg