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.

Abstract: A percussion drill bit for drilling into a subterranean earth formation. The drill bit has a central longitudinal axis and is operable by applying repetitive axial percussive impacts on the drill bit in a direction having a component along the axis and by applying rotary motion about the axis relative to the earth formation. The drill bit is provided with one or more axial cutters for predominantly axially cutting the subterranean earth formation in response to the axial percussive impacts and one or more shear cutters for predominantly shear cutting the subterranean earth formation in response to the rotary motion. There is a first shear cutter of the one or more shear cutters, and one or more of the axial cutters are arranged with respect to the first shear cutter to engage with the subterranean earth formation earlier during a percussive impact than the first shear cutter.