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: The invention relates to a drill bit assembly for fluid-operated percussion drill tools comprising a percussion bit (1) having a head portion (3) formed with an axially extending stub shank (32). The stub shank is provided with axially extending splines (36), which are slideably engageable with complementary splines (35) formed on a drive chuck (4). Rotational drive from the chuck (4) may be transmitted to the stub shank (32) by means of the splines. Bit retaining means (6, 7, 41, 42) at the chuck are adapted for engagement with complementary retaining means (37, 51) at a spline portion of the stub shank to retain the stub shank in the drill bit assembly. Engagement means on the chuck (4) are adapted for connecting the chuck (4) to a drive means (5) of the fluid-operated percussion drill tool.

Abstract: A downhole percussive tool is disclosed comprising an interior chamber and a piston element slidably sitting within the interior chamber forming two pressure chambers on either side. The piston element may slide back and forth within the interior chamber as drilling fluid is channeled into either pressure chamber. Input channels supply drilling fluid into the pressure chambers and exit orifices release that fluid from the same. An exhaust orifice allows additional drilling fluid to release from the interior chamber. The amount of pressure maintained in either pressure chamber may be controlled by the size of the exiting orifices and exhaust orifices. In various embodiments, the percussive tool may form a downhole jack hammer or vibrator tool.

Abstract: A drill bit assembly comprises a bit body intermediate a shank and a working face. The shank is adapted for connection to a drill string. The drill string comprising a fluid passage at least partially disposed within the body. A hammer assembly is movably disposed within the fluid passage along it central axis, the hammer assembly comprises a proximal end stabilized by a centralized upper bearing and a distal end stabilized by centralized a lower bearing. The distal end protrudes out of the working face and the hammer assembly comprises a carrier between the upper and lower bearings. Wherein, under normal drilling operations the carrier is adapted to resist a fluid pressure within the fluid passageway such that the fluid pressure will further extend the distal end of the hammer assembly from the working face by pushing on the carrier.

Abstract: A drill bit assembly comprises a bit body intermediate a shank and a working face. The shank is adapted for connection to a drill string. The drill string comprising a fluid passage at least partially disposed within the body. A hammer assembly is movably disposed within the fluid passage along it central axis, the hammer assembly comprises a proximal end stabilized by a centralized upper bearing and a distal end stabilized by centralized a lower bearing. The distal end protrudes out of the working face and the hammer assembly comprises a carrier between the upper and lower bearings. Wherein, under normal drilling operations the carrier is adapted to resist a fluid pressure within the fluid passageway such that the fluid pressure will further extend the distal end of the hammer assembly from the working face by pushing on the carrier.

Abstract: A rock drilling machine includes a frame, and arranged inside the frame is a drill rod. A hammer gear is arranged to hammer the drill rod rear end. There is arranged around the drill rod a position sleeve and an arrangement to move position sleeve in an axial direction against hammering piston so that a counter surface of the position sleeve meets the counter surface whereby, on continuing the positioning, the drill rod is movable to the point desired. The counter surface by use of a spring element is arranged to flex in regard to the other structure of the position sleeve so that in the drilling position the sleeve is arranged to be freely backing against the front side of the drilling machine, and when in the drilling operation the positioning impact on the position sleeve against the hammering piston is removed.

Abstract: According to one aspect of the invention there is provided a rotary-vibratory drilling apparatus. The drilling assembly is comprised of a vibratory apparatus, a rotary drive apparatus, a drill string, a first conduit and a second conduit. The first conduit communicates with the second conduit and the second conduit communicates with the drill string. The drilling assembly may further include a fluid reservoir communicating with the first conduit. Fluid may be discharged from the fluid reservoir into the first conduit, fluid may be discharged from the first conduit into the second conduit, and fluid may be discharged from the second conduit into the drill string. The first conduit may be threadedly connected to the second conduit.

Abstract: A separate drilling head has a distal end which contacts the material to be drilled, and a proximal end which is attached to a drive mechanism. The drive mechanism drives the separate drilling head into the material. The separate drilling head is forcelockingly secured in a thin-walled hollow anchor tube, and the separate drilling head includes a hard metal cutter element, and a substantially axially-oriented, axial stop shoulder at the proximal end that passes into a circumferentially closed, outer cone.

Abstract: A solid hard material head for a percussion drilling tool rotatable about a rotational axis (A) in a rotational direction (?), includes at least one main bit and at least one auxiliary bit (5), circumferentially offset relative to the at least one main bit (3) and having an auxiliary cutting edge (6) formed, at least piecewise, as a circular arc section (7) spaced from the rotational axis (A) radially inwardly and inclined in a radial direction, and a straight outer section (8) extending radially outwardly with respect to the circular arc section (7) and inclined in the radial direction.

Abstract: A hard material head (1) for a rotary percussion drill bit (2) having an elongated shaft (15) including at least three cutting edges (4) distributed circumferentially within a circumscribing circle, a bottom surface (6) located opposite the cutting edges (4) and fastened by a material bond to an end (8) of the drill bit shaft (15) of the rotary percussion drill bit (2), concave side surfaces (5) formed circumferentially between adjacent cutting edges (4), and a peripheral pocket (9) opening toward the bottom surface (6) and formed, respectively, in at least two concave side surfaces (5) located opposite one another, and in which a corresponding axial pin (10, 10?) formed on a shaft end (8) is form-locking engageable.

Abstract: A hard material bit for a rotary-percussion tool (2) includes at least one cutting edge (3), a bottom surface (6) located opposite the at least one cutting edge (3), and at least one attachment surface (8) and at least one free surface (10) both extending transverse to the bottom surface (6) and forming, respectively, a piecewise extending first chamfer (9a) and second chamfer (9b), with the second chamfer (9b) having a width greater than a width of the first chamfer (9a).

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.

Abstract: A percussive drill bit has a working face opposite a shank end. The working face has a central jack insert and a plurality of peripheral inserts extending from the working face. The ends of the plurality of the peripheral inserts form an impacting plane. The central jack insert is disposed within a recessed portion of the working face and has an end extending between the working face and the impacting plane.

Abstract: The present invention relates to a percussion hammer for enlarging drilled holes. The hammer comprises an external outer wear sleeve (5), an inner cylinder (7) mounted co-axially within the outer wear sleeve (5), a tubular torque shaft (3) disposed axially and centrally of the hammer assembly, and extending longitudinally through the assembly. The hammer further comprises a sliding piston (6) mounted for reciprocating movement within the inner cylinder (7) and outer wear sleeve (10) and about the tubular torque shaft (3) to strike a hammer bit (1) for reciprocal movement in a chuck (4) adjacent a forward end of the hammer assembly. The hammer bit (1) has a central bore (46) through which the torque shaft (3) extends, such that the torque shaft (3) protrudes forwardly of the hammer.

Abstract: A drill bit for a hammer drill for drilling in stone, concrete and the like includes a drill bit head formed as a hard material body with radial legs and having at least three radially extending cutting bits formed on the radial legs, and a centering tip in a center of the hard material body and projecting beyond one of the cutting bits, with the centering tip having concave limiting surfaces stretching between the linearly extending auxiliary cutting edges.

Abstract: A drilling apparatus includes a cutting structure defined by a percussive action cutter and at least one other cutter. The percussive action cutter is adapted to be urged in a drilling direction by hydraulic pressure force, while the other cutter is urged in a drilling direction by mechanical force.

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 axial percussive motion along the axis and rotary motion about the axis. The drill bit is provided with a plurality of blades protruding from the drill bit and, a plurality of flow channels stretching along the drill bit in a substantially radial direction whereby the successive flow channels are formed between two adjacent blades. Shear cutters are provided in a row on or close to the leading edge of at least one of the blades with respect to the direction of rotary motion trailingly adjacent to the flow channel that is associated with it. A fluid may be run through the flow channel to remove cutting debris accumulating in front of the row of shear cutters. In addition to these shear cutters, axial cutters are located, with respect to the direction of rotary motion, in a trailing position with respect to the row of shear cutters and its associated flow channel.

Abstract: A pneumatic rockdrill having a housing; a cylinder connected to a compressed air supply inlet by a set of air passages; an impact piston, at least part of which is reciprocable within the cylinder; and a controller for the supply of compressed air from the air supply inlet to the cylinder. At least one pair of contact surfaces are located at the interface between the piston and the cylinder, where those relatively moving parts contact one another. At least one water supply inlet and water paths connected to the water supply inlet(s) are configured so as in operation to convey water to a drilling tool to flush a hole being drilled, and to supply water to wet the contact surfaces.

Abstract: The invention relates to a percussion mechanism for an at least percussively-operated hand machine tool, in particular a hammer drill or chisel, comprising a drive motor and a tool holder (10) for housing a tool, with a percussive pin (12) acting on the tool which is axially displaceable within a percussive pin guide (11). The percussive pin guide (11) has a body (13) enclosing the percussive pin (12). According to the invention, the body (13) is made from two materials of differing hardness. The invention further relates to an at least percussively-operated hand machine tool, in particular a hammer drill or chisel with a percussion mechanism.

Abstract: A drive collar is disclosed for use in a percussion drilling apparatus of the type for boring into the earth. Embodiments of the drive collar include a generally tubular, one-piece body further having an inner surface, an outer surface, a first end and a second end. Embodiments further include a threaded section on the outer surface, a retention mechanism on the inner surface, a plurality of splines on the inner surface; and a shoulder on the outer surface.

Abstract: In one aspect of the present invention a drill bit assembly comprises a working portion opposite a shank of the bit. The working portion has a plurality of cutting elements. The drill bit assembly also has a central axis eccentric to its axis of rotation. A jack element protrudes from an opening formed in the working portion and has a distal end that is adapted to contact a formation at the axis of rotation.

Abstract: A multi-sectional percussive drill bit assembly for drilling holes in earth formation primarily used in conjunction with a pneumatic percussive device. The drill bit assembly is comprised of an easily removable bit that is rotationally driven by a lug and pocket structure and axially limited in travel by means of retaining members.

Abstract: An apparatus (10) for use in boring is described, the apparatus including a rotatable drive shaft (12), a cam member (20) and followers (16) for converting rotational motion into reciprocal motion, and a shroud (24) having a cutting edge (26) driven by the cam member and followers. The shroud may be selectively engageable with the cam member and followers, allowing the drive shaft to be removed through the shroud. A fluid circulation arrangement (31), (13) allows air to be injected into loose drilling substrate, so assisting removal of drill cuttings from the boring apparatus. Also described is a drill string incorporating a similar arrangement, allowing the drill string to be reciprocated within a bore. The drill string may further include casing sections, which may have intumescent coatings to allow the sections to be fixed in a wellbore.

Abstract: The present invention relates to a multi-purpose drilling tool with a boring head, a drill twist connected thereto and a downstream clamping shank, a cutting element (1) being provided on the working side of the boring head. The cutting element (1) has a face (9, 24) with a rake angle (?) having a value of ??0° b, the cutting element (1) having a flank (10, 13) with a lip clearance angle (?) having a value of 5°???15° and, in particular, ??10°.

Abstract: A portion of a drilling tool having a drill bit driven in a rotating motion and in an axial percussion motion comprises a keyed connection between the drill bit and a driver sub that receives the drill bit. The keyed connection comprises a transverse member coupling the drill bit to a driver sub having a bore within which the drill bit is received. The driver sub has a pair of opposed openings and the bit has an axial slot. The openings and the slot are dimensioned to receive the transverse member. The keyed connection transmits force to the drill bit to drive the drill bit during operation and removably secures it in the driver sub.

Abstract: A rotary-percussion drill, includes a hard material bit (2, 2?) having at least one cutting edge (3, 3?), and a shaft having an end (7, 7?) with an axial base surface (6, 6?) provided with a chamfer (8, 8?) at least on its outer radial rim, the bottom surface (4, 4?) of the bit (3, 3?) which lies opposite the cutting edge (3, 3?), being secured to the base surface (6, 6?) of the shaft end (7, 7?) by brazing alloy in a material-locking manner.

Abstract: A multi-sectional percussive drill bit assembly for drilling holes in earth formation primarily used in conjunction with a pneumatic percussive device. The drill bit assembly is comprised of an easily removable bit that is rotationally driven by a lug and pocket structure and axially limited in travel by means of retaining members.

Abstract: A solid hard material head for a percussion drilling tool rotatable about a rotational axis (A) in a rotational direction (?), includes at least one main bit and at least one auxiliary bit (5), circumferentially offset relative to the at least one main bit (3) and having an auxiliary cutting edge (6) formed, at least piecewise, as a circular arc section (7) spaced from the rotational axis (A) radially inwardly and inclined in a radial direction, and a straight outer section (8) extending radially outwardly with respect to the circular arc section (7) and inclined in the radial direction.

Abstract: A one-piece drilling head (4) which is to be secured, in a material-locking manner, at an end of a helical shaft of a drill, is formed of hard material and includes four radially extending, in a cross-shaped manner, legs (5) forming, respectively, two diametrically opposite main cutting edges (6) and two auxiliary cutting edges (7), with the main cutting edges (6) and the auxiliary cutting edges (7) extending proceeding from a drilling head drilling head tip (8), monotonously and strictly axially up to a radially outer edge, and with an envelope surface (9?) of the auxiliary cutting edges (7) lying completely within an envelope surface (9) of the main cutting edges (6) and contacts the same only at the drilling head tip (8).

Abstract: A percussion or hammer drill is provided including a drill plate arranged in the head end of a drill shaft, extending completely across the diameter of the drill shaft and comprising an open front face. Wedge-shaped cutting edges and flanks form two main cutters on the front face, whereby a plane running through the drill axis forms a mid-plane-of both main cutters. The main cutters form a tip angle in the range of approximately 140° to 180° and are separated by a central point.

Abstract: The invention relates to a method and device for the drilling, in particular the percussive drilling or rotary percussive drilling of holes (9) in the ground or in rock, a bore hole (9) being formed by a drill bit (1) that is mounted on a drill pipe (3), by a percussive and/or rotary movement. Several drill points (2), which can be coupled to the drill pipe (3) and driven independently of one another, are provided on the drill bit (1). According to the invention, the drill points (2) can be uncoupled from their rigid coupling to the drill pipe (3) upon completion of the drilling process and can be displaced towards the centre of the bore hole (9), thus permitting the entire drill bit (1) together with the drill points (2) and the drill pipe (3) to be simply and reliably removed upon completion of the bore hole (9).

Abstract: A hard material bit for a rotary-percussion tool (2) includes at least one cutting edge (3), a bottom surface (6) located opposite the at least one cutting edge (3), and at least one attachment surface (8) and at least one free surface (10) both extending transverse to the bottom surface (6) and forming, respectively, a piecewise extending first chamfer (9a) and second chamfer (9b), with the second chamfer (9b) having a width greater than a width of the first chamfer (9a).

Abstract: A drill bit has a body intermediate a shank and a working face and has an axis of rotation. The working face has at least one cutting element and the body has at least a portion of a jack assembly. The jack assembly has at least a portion of a shaft disposed within a cavity formed in the body of the drill bit, the shaft having a distal end extending from an opening of the cavity formed in the working face. The jack assembly also has an electric motor and/or generator.

Abstract: A shank for a working tool has at least three recesses (5) provided within the lockable region (3) and arranged in a cross-section (c-c) to the tool axis (A) at least at angles of 0°, 120°, and 240° within the radial reference dimension (R) of the shank, with at least one of the recesses (5) being axially closed toward a free end of the shank (1), and at least one protrusion (6) arranged circumferentially between two adjacent recesses (5) outside of the radial reference dimension, with the sum of central recess angles (?) of the recesses amounting to at least 150°, and a central protrusion angle (?) of the at least one protrusion (6) being smaller than a central recess angle (?).

Abstract: A separate drilling head (1) which is to be forcelockingly secured in a thin-walled hollow anchor tube (3), includes a hard metal cutter element (2), and a drive-side, substantially axially oriented, axial stop shoulder (4) that passes into a circumferentially closed, outer cone (5).

Abstract: A rotary hammerdrill bit for use with a percussion drilling device or a hammer drilling device, with a shank and a drill head attached to or configured on the shank, wherein a front side pointing in the advance direction of the drill head has a main cutting plate forming a main cutting axis. The main cutting plate extends over the diameter of the drill head and has a tip or tip-edge lying in the longitudinal axis of the drill bit and forms drill blades that are substantially roof-shaped and are inclined radially from the tip or tip-edge. The front side of the drill head has at least one pair of cutting pins, wherein the cutting pins are arranged on the drill head in essentially the same radial positions.

Abstract: A back bit (20) is disclosed which is to used in conjunction with drilling equipment (10) which may include a derrick (11), a drilling pipe (12), a back head (14), a starting rod (13), and a cutting bit (15) mounted to the lower end of the starting rod. The back bit has a tubular body (21) with a plurality of upwardly extending cutting teeth (22).

Abstract: In a method and device for drilling, in particular percussion drilling or rotary percussion drilling, holes in soil or rock material, wherein a borehole is formed by a percussive and/or rotational movement carried out by a drill bit (1) mounted on a drill rod assembly (4) and an envelope tube and/or a jacket tube (15, 18) is introduced into the borehole, it is provided that the impact energy introduced by the drill rod assembly (4) is transmitted partially, particularly centrally, by the drill rod assembly (4) onto the drill bit (1) and partially via an impact shoe (10) cooperating with the drill rod assembly (4) onto the envelope and/or jacket tubes (15, 18), thus enabling the reliable introduction of the excavation or impact energy into the drill bit (1) as well as into the envelope and/or jacket tubes (15, 18).

Abstract: A drill bit has, on its face, a combination of at least one straight cutting edge and at least two curved cutting edges arranged in a Y-shape. The cutting edges on the face of the drill bit are arranged such that they start from the axis of the drill bit or end directly adjacent thereto. The straight cutting edge is symmetrical with respect to the curved cutting edges, which are curved in opposite directions.

Abstract: An auxiliary cutting plate (10) for a multi-cutting plate drill bit (2) has a body (44) for fixing into a slot in the drill bit (2) and a profiled tip (46). The body (44) has a central longitudinal axis and the profiled tip (46) protrudes from one end of the body (44). The profiled tip (46) has a cutting edge (62) defined by a transition between a rake face (64) and a relief face (66). The rake face (64) and the relief face (66) each slope axially rearward from opposite sides of the cutting edge (62). The angle of inclination ? of at least a portion of the rake face (64), measured from a plane perpendicular to the longitudinal axis, decreases with increasing distance from the cutting edge (62).

Abstract: A drilling apparatus comprises a casing shoe, ring bit, and center bit. The casing shoe may be connected to a casing received within the casing shoe. The ring bit is received within the casing shoe and retained at the end of the casing. The ring bit rotates relative to the casing shoe, and drills a peripheral portion of a hole. The center bit drills a central portion of the hole, and may be rotated and percussively driven to drill the hole. The center and ring bits are adapted for: engaging one another so that rotating and percussively driving the center bit also rotates and percussively drives the ring bit; engaging one another so that retracting the center bit also retracts the ring bit, casing shoe, and casing; enabling disengagement from one another and withdrawal of the center bit from the ring bit and the casing shoe.

Abstract: A percussive drill bit or reamer having a plurality of bit segments formed into a circular pattern suitable for drilling or reaming a hole. The bit segments are close-fitted and shaped to increase the cutting area and improve efficiency. Pressurized air exhausted from driving the percussion mechanism, or provided from a separate source, is passed into the bit segment and exits from a side face thereof into the gap formed between adjacent bit segments, thereby driving out any debris present in the gap and preventing binding of the bit segments. When utilized with mechanically-driven percussive bit assemblies, where air is only needed to remove debris from a rock face, separately-provided air is delivered to the bit segments of the present invention as described above to clear the gaps of debris.

Abstract: A drill bit constructed to improve a tip end of the cutting pointed portion to efficiently discharge chips from a center portion of a crush face of a drill hole to thereby improve cutting efficiency, is disclosed. A plurality of cutting blades 3a, 3b, and 3c are formed to be arranged in a circumferential direction of a cutting blade chip 3 formed by a cemented carbide block body. The cutting blades 3a, 3b, and 3c are each structured to have a cutting edge 4 formed by an edge between a face 6 and a flank 7 of the associated cutting blades. In this drill bit, a groove 8 is configured to be provided in a center portion of the tip end of the cutting blade chip in contact with tip ends of the cutting blade chip, and the tip ends of the cutting edges 4 have pointed portions.

Abstract: A bit assembly for a hammering and rotating drill, in which a main drill body (1) is arranged to drill essentially a middle portion of the hole and in the main drill body (1) there is mounted one or more outer bits (2),(3) arranged to drill an outer circle of the hole. The outer drilling bits (2),(3) are arranged to drill an outer drilling surface which is located behind a middle drilling surface of the main drill body in the drilling direction. The outer bits (2),(3) are further mounted in the drill body (1) in formed counter cavities (7), the axial directions (S) of which are either the same direction as the drilling direction or which deviate outwards from the drilling direction. The outer bits can be moved at least a part of the way out of the counter cavities, in order to be moved in a direction which deviates from the axial direction (S) of the counter cavity.

Abstract: Device and method for drilling into geological formations. The device comprises: a rotatable body; drilling cutters arranged on an axial end surface of the rotatable body; a percussion part, which is parallel to the rotating axis reciprocatable arranged on said body; and percussion cutters arranged on an axial end surface of the percussion part. The method comprises the steps of: bringing a percussion part with a percussive movement in contact with the formation in order to crack at least a part of the formation, and scraping the cracked parts of the formation with a drilling part.

Abstract: An object of the present invention is to provide a drill bit which is simple in design, high in rigidity, and superior in durability and whose drilling function is in no way inferior to that of conventional drilling bits. To this end, in a drill bit comprising a cutting blade tip 2 which is united tightly to a tip end of a bit body 1 and a plurality of cutting blade portions 2a, 2b and 2c which are formed around the cutting blade tip 2, a flat surface portion 3 is formed in a side surface of the drill bit from between adjacent cutting blade portions to a base portion of the bit body 1 so that the bit body 1 is formed into a straight configuration having an approximately polygonal cross section.

Abstract: A drill bit comprises, on its face, either only curved cutting edges or a combination consisting of at least one straight cutting edge and at least two curved cutting edges. The cutting edges on the face of the drill bit are arranged such that they start from the axis of the drill bit or end directly adjacent thereto. Three channels start from a blind hole serving to attach the drill bit to an anchor rod of an injection boring anchor, and their openings are not located in the area of the face of the drill bit but are situated in the area of the lateral surface of the same, said lateral surface conically expanding toward the cutting edges. The openings of the channels are placed in the area of concave recesses of the lateral surface of the drill bit in such a manner that they are recessed with regard to the periphery of the face of the drill bit.

Abstract: A cutting plate (4) has a working end (20) to engage a workpiece and an axis (8) of rotation. A pair of oppositely arranged first faces (34) are inclined axially rearward from the working end (20) in an axial plane intersecting said first faces (34). A pair of second faces (30) are alternately arranged between the first faces (34). The second faces (30) are inclined axially rearward from the working end (20) in an axial plane (37) intersecting the second faces (30), and a pair of axis parallel front faces (24). Each of the front faces (24) is bound on three sides by a respective first face (34) and the pair of second faces (30). Each second face (30) is inclined radially inward from a transitional edge with a respective rotationally leading first face (34) in a plane normal to the axis (8) intersecting the transitional edge with a respective rotationally leading first face (34).

Abstract: A cup-shaped drill head with an inner conical surface (2) for force-locking connection with an exterior conical surface (3) of a driving drill shaft (4), which at the leading end changes over into a cup base (5) with a center point (P), whereby in the change over from the cup base (5) to the inner conical surface (2) a lesser curvature (K) is present than at the center point (P).

Abstract: A concrete drill for a rotary and percussively driven hand tool machine with a cutting part (1) and a striking part (2) that is axially and limited displaceable relative to the cutting part (1). Each of the cutting part (1) and the striking part (2) have a respective facial surface work area for machining a bore hole surface. The respective facial surface work area of the cutting part (1) and the striking part (2) radially overlap upon rotation of the concrete drill.