Abstract: Uneven wear of the cutting edges of rotating trepanning or drilling tools is avoided by employing at least two cutting blades, by providing a single support strip embedded in an elastically pliable material, and by arranging the cutting blades such, that the resultant force of the cutting forces produced during the drilling operation is directed to the support strip and is of a magnitude such that the lubricant film bracing said strip against the borehole wall does not break away.

Abstract: A drill for rock comprising a boring head arranged on one end of a drill shank and having radially projecting wings, an axial centering projection which projects in a boring direction in front of the wings, said wings and said projection constituting carriers of eccentrically arranged cutter bodies and a centering cutter body, respectively. Breaker surfaces are formed on the wing surfaces between the cutter bodies, respectively, pointing to the centering point of the centering cutter body. Each surface of the boring head located between the wings has at least one jacket line which extends longitudinally to the axis of the boring head and directly joins to a jacket line of the outer surface of the centering projection and is inclined relative thereto at an obtuse angle.