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Abstract

A drill bit for drilling a borehole in an earth formation. The drill bit has a central longitudinal axis and may be operated by applying at least a rotary motion about the central longitudinal axis and optionally applying longitudinal reciprocal movement to the drill bit so as to exert a percussive force on the borehole bottom. The drill bit has a surface provided with a plurality of shear cutters having a rake surface arranged to induce a scraping movement along the borehole bottom upon application of the rotary motion. The rake surface, during operation, faces the direction of rotation at a back-rake angle of less than 90°, wherein the backrake angle is defined as the angle included between the projection of a line perpendicular to the rake surface on a plane defined by the central longitudinal axis and the direction of the tangential velocity component of the shear cutter and a plane perpendicular to the longitudinal axis. One or more of the shear cutters is provided with a pre-cut flat impact surface essentially parallel to the plane perpendicular to the longitudinal axis.

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First Claim