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 mortar removal drill bit system includes a toothed drill bit that includes an elongated rod that has a first end and a second end. A plurality of rectangular plates is attached to and extends laterally from the rod. Each of the plates has a distal edge with respect to the rod. Each of the distal edges is orientated parallel to a longitudinal axis of the rod. The first end of the rod is removably extendable into and attached to a drill.

Abstract: A system for boring horizontal boreholes and installing products using a dual member drill string. The system is comprised of a boring machine with a frame and a rotary drive supported on the frame, a downhole tool, and a dual member drill string. The drill string comprises an inner member disposed within a tubular outer member such that the inner member is rotatable independent of the outer member. The outer member has at least one helical projection supported on an exterior surface of the outer member. The projections on the outer member function as an auger to clear spoils and support the bore. The auger arrangement with the dual member drill string can be used in forward reaming or backreaming operations.

Abstract: A downhole tool (10) for use in oil and/or gas well bores. The tool has a tubular body (20) and a sleeve (22) including stabilizer blades (30). The tool is ball (76), activated, weight activated or hydraulically activated to selectively jet fluid from the body through jetting ports (44A, 44B, 44C) on the blades. Thus the tool provides the features of a stabilizer, cleaning tool and circulation tool in-one.

Abstract: The present invention provides an apparatus (10) and method for transmitting torque to a downhole device. The apparatus (10) comprises a first part and a second part adapted for connection to the downhole device. The apparatus (10) also comprises an engagement means (100, 120). The first and second parts are connected together such that relative axial movement between the first and second parts is constrained on a helical path. The engagement means (100, 120) are arranged to rotationally connect the first and second parts to thereby transmit torque from the first part to the second part when a coupling point is reached on the helical path.

Abstract: A system for damping vibration in a drill string can include a valve assembly having a supply of a fluid, a first member, and a second member capable of moving in relation to first member in response to vibration of the drill bit. The first and second members define a first and a second chamber for holding the fluid. Fluid can flow between the first and second chambers in response to the movement of the second member in relation to the first member. The valve assembly can also include a coil or a valve for varying a resistance of the fluid to flow between the first and second chambers.

Abstract: A rock head for use with an auger borer to bore a passageway through a body of soil and rock and simultaneously laying a pipe in that bored passageway. The rock head has a base connectable to the leading end of the auger. A plurality of movable mounts are provided on the base and a roller cone is secured to each movable mount. A spring is disposed between the movable mount and the base. The spring is compressed as the movable mount pivots the roller cones inwardly toward a central region of the base. This reduces the diameter of the rock head so that it can travel through the bore. Each movable mount is provided with at least one wheel so that it can ride smoothly through the bore. When the rock head exits the pipe, the springs automatically pivots each roller cone outwardly so that at least a portion thereof is disposed beyond the outermost edge of the base. In this second position, the rock head has a greater diameter than the pipe bore and therefore it cannot travel therethrough.

Abstract: An earth auger presents a shank having a spiral earth removing structure therearound. The structure first presents a series of spirally positioned housings with cutting teeth therein followed by a spiral cutting edge about the shank. The teeth are radially, vertically and angularly oriented so as to remove earth in a stair-step fashion with a pneumatic drill-like action. The cutting teeth are further arranged so that each subsequent cutting tooth, as measured from the initial shank penetrating end, removes earth prior to the contact of the preceding cutting tooth housing so as to preclude earth contact. The earth relief, the spiral cutting teeth arrangement, the radial displacement of the teeth relative to the shank, the vertical displacement among the teeth and the angular relationship of the teeth, alone and in combination, enhance drilling.

Abstract: An adapter attachment for an auger which includes an connecting shaft sized and shaped to be attached to the pilot bit hole present in the end of an auger, after the removal of pilot bit. The adapter also includes a bolt flange for connection to a foundation anchor installation plate/tool such as a locking dog assembly. The adapter obviates the need to remove the auger from the Kelly bar during anchor installation. A modification includes eliminating the bolt flange and placing the connecting shaft directly to the locking dog assembly to form a pilot hole locking dog.

Abstract: A system for boring horizontal boreholes and installing products using a dual member drill string. The system is comprised of a boring machine with a frame and a rotary drive supported on the frame, a downhole tool, and a dual member drill string. The drill string comprises an inner member disposed within a tubular outer member such that the inner member is rotatable independent of the outer member. The outer member has at least one helical projection supported on an exterior surface of the outer member. The projections on the outer member function as an auger to clear spoils and support the bore. The auger arrangement with the dual member drill string can be used in forward reaming or backreaming operations.

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: An auger planter for forming small holes in the earth for the planting of flower bulbs, plant seedlings and plants, and for the insertion of termite monitors and baits. The auger includes a central shaft and a single helical flighting having its leading edge configured to have a sickle blade shape with a cutting edge. The opposite end of the flighting has a portion which is directed in an essentially vertical orientation proximating an alignment parallelling the axis of shaft.

Abstract: A downhole tool including a selectively releasable joint, a downhole drilling assembly including the downhole tool, and a corresponding method. In one embodiment of the invention, a downhole drilling assembly includes a downhole tool having a first body and a second body mounted for relative rotation; a joint part for use in forming a selectively releasable joint between the second body and a part of the assembly coupled to the second body; and one or more locking member(s) for locking the first and second bodies relative to one another against relative rotation so as to allow a release force to be applied through the first body to release the releasable joint and allow the tool to be separated from the part of the assembly.

Abstract: The auger is attached to a spiral gear and a spring, the apparatus then being connected to the downhole, leading end of the logging sonde. When the auger nose of the modified sonde assembly strikes any of various obstructions on the sidewall that cause it to lose momentum, such as a rock ledge, the momentum of the heavy sonde causes the auger nose assembly to compress, forcing the auger to rotate on the spiral gear. The rotational action thus produced allows the auger to pull the sonde to pass the obstruction. After the obstruction has been passed, the potential energy stored in the spring induces the auger to return to its original extended position, whereupon it is ready to encounter and pass another obstacle.

Abstract: A reversible post hole digger apparatus powered by a power takeoff shaft includes a transmission providing a reverse gear and a forward gear in a single housing. The apparatus has a power head disposed between a shaft connected to the power takeoff and an output shaft driving an auger. A gear box within the power head contains a main shaft which carries forward and reverse pinion gears at opposite ends and has a central portion with an external spline connector. The pinion gears are activated by a central spline-containing slide. Movement of the slide, carried out by means of a shift lever engaging a fork with a rack and pinion device, provides connection to forward, reverse and neutral positions on the shaft. Upper and lower ring gears drive an output shaft in a selected direction.

Abstract: An auger bit is provided for a foundation pile system including a drilling rig adapted for mounting and rotating a grout pipe connected to the auger bit to form an auger. The auger bit includes a stem with lower and upper sections, which taper towards a transition whereat the stem has a maximum diameter. A pile foundation forming method includes the steps of providing a drilling rig, forming an auger with a grout pipe coupled to an auger bit, rotating the auger wit the rig, forming a borehole with laterally displaced soil, pumping pressurized grout through the auger and into the borehole, placing a reinforcing cage in the wet grout and curing same.

Abstract: An auger support assembly for use with an augering system for mining which bores a pair of side-by-side holes through a coal seam using dual side-by-side augers. Each auger includes a drilling section which is followed by a series of auger flights for conveying the bored coal back out of the respective hole. The augers are connected together in axially aligned pairs and are supported by the auger support assembly. The auger support assembly includes a pair of bearing housings that are disposed on drive shafts which extend outwardly from the first ends of a first pair of parallel augers and are received within the second ends of a second pair of parallel augers. The bearing housings are connected to each other by a tie bar. A single support leg extends downwardly from approximately the mid-section of the tie bar to engage the ground ledge that is formed between the counter rotating augers.

Abstract: The drill string element has at least one bearing zone for bearing against the wall of the borehole during drilling. The bearing zone comprises at least one bearing segment extending in the axial direction and having an outside surface that is cylindrical and of constant diameter greater than the diameter of any other portion of the surface of the element, and also having a guide zone that is circularly symmetrical about the axis of the drill string element. The bearing zone preferably also has a drilling fluid activation zone extending axially in a disposition adjacent to the bearing segment. The guide zone presents a radius of curvature not less than one-third the outside diameter of the bearing segment.

Abstract: A drill string tool such as a drill string stabilizer (1) comprises a circumferentially continuous bearing sleeve (6) having an outside diameter which is equal to or greater than the outside diameter of a radially outermost part of the drill string tool.

Abstract: A drill-string member includes at least one grooved portion on an outer surface thereof. A pair of axially spaced-apart grooved portions are typically provided, with two such pairs axially spaced along the longitudinal length of the member. A plurality of grooves are milled into the grooved portions, and the grooves intersect with one another to form a criss-cross pattern. As the member is rotated, fluid flows up the grooves, where fluid from one groove meets fluid from another groove at each intersection, causing turbulence to be created.

Abstract: The invention concerns a drill including a generally cylindrical body, tipped with a head and provided, over at least part of its length, generally spiral evaporating grooves. The groove(s) are delimited, over at least part of their length, by a succession of facets, attached to one another, and linked to one another by sharp edges or by radius blends.

Abstract: A cutting auger has a main auger blade and a front subsidiary coaxial blade each having a drive core and a helical auger flight carried on the drive core for rotation about a longitudinal axis of the drive core with a cutting edge at an axial end face of the auger flight, such that when rotated the cutting edge cuts a hole equal in diameter to the helical flight and the helical flight carries the cut material away from the cutting edge. The second auger blade having a smaller diameter than the first, is shorter than the first and is arranged with the helical turns thereof in opposed angular direction. A planetary drive system is arranged to rotate the first and second cutting augers in opposed direction with the first driven at a slower angular velocity than the second so as to balance the torque.

Abstract: A masonry or rock drilling tool suitable for use with a rotary hammer has a drilling head (4, 104) at a forward end of the tool. A forwardly extending cutting plate (6, 106) is fitted or formed on the drilling head (4, 104). First and second opposing axially extending channels (36, 38, 136, 138) are formed on the circumferential periphery of the drilling head. The tool has a clamping shank (2, 102) at a rearward end of the tool suitable for fitment within a tool holder of a rotary hammer. An intermediate helical conveying portion (10, 110) extends between the drilling head and the clamping shank. The intermediate helical conveying portion has at least four helically extending flutes (14a–d, 114a–d) separated by corresponding helically extending webs (12a–d, 112a–d). The first of the axially extending channels extend axially rearwardly from a forward facing face of the drilling head into two of the four flutes.

Abstract: An adjustable hole cleaning device is provided for cleaning a hole in a subterranean formation. A drillstring containing the device is rotated to drill a hole through the subterranean formation. While rotating the drillstring, drilling fluid is circulated through the drillstring and the device into the hole. In response to an increase in a hydrostatic pressure of the fluid in the drillstring, cleaning elements are extended from the device to clean accumulated cuttings from the drilled hole. The cleaning elements may clean the accumulated cuttings by agitating the circulating fluid in the hole. In response to a decrease in a hydrostatic pressure of the fluid in the drillstring, the cleaning elements may be retracted back into the device. The device may also include a set of ports which hydraulically open in response to the increase of hydrostatic pressure in the drillstring to disperse drilling fluid into the hole for cleaning accumulated cuttings.

Abstract: A torque absorber is disposed on a drill string near the motor. The torque absorber automatically adjusts the weight on a drill bit and reduces the likelihood of motor stall caused by resistance to drill bit rotation. The torque absorber includes an upper unit assembly and a lower unit assembly. The upper unit assembly includes a top sub and a ball body. The lower unit assembly includes a bottom sub, a lead screw, and a ball retainer. The components of the lower unit assembly are free to rotate as a result of motor back torque, which is in a direction opposite of the direction of rotation of the drill bit during normal drilling. The upper unit assembly will remain stationary while the components of the lower unit assembly rotate in this opposite direction. A spring applies a force on the lead screw.

Abstract: A drill string member is formed by providing a former and a cylindrical member to be shaped in relationship with the former. Seals are provided between opposing ends of a thick wall cylinder and the cylindrical member, a pressure is applied in the annulus between the cylindrical member and the thick wall cylinder sufficient to deform the cylindrical member against the former. The drill string member thus formed has a constant wall thickness and a non-circular former provides a non-circular drill string member.

Abstract: Device for producing bored piles having an auger, which along at least part of the auger length is surrounded by a rotating encasing tube and during boring the encasing tube is rotated in or counter to the rotation direction of the auger and in which the auger and the encasing tube are introduced essentially simultaneously into the ground during boring. To facilitate material discharge, the surface roughness of the auger helix surface pointing in the feed direction is increased compared with the roughness of the rolled surfaces in a complete or partial surface manner by additional machining. The increase in the surface roughness extends at least over the auger length necessary for feed purposes.

Abstract: The invention relates to a method of boring a hole using a boring system constituted by a simple auger and a dip tube slidably mounted in said auger, said dip tube being provided at its bottom end with a tool. The method comprises the following steps: causing said auger and said dip tube to descend and to rotate simultaneously, said tool on the dip tube being substantially level with the bottom end of the auger; interrupting the descent and rotation of said auger so that the auger constitutes anchor means for anchoring the boring system in the ground; and causing the dip tube to descend and rotate on its own, whereby the tool of the dip tube performs boring by displacing ground at the bottom end of the borehole, thereby compacting the ground.

Abstract: The stabilizer (1) has a tubular central body (3) having means for connection (3a, 3b) to a first and a second component of the string of drill rods and at least one external contact element (4) with a wall (2a) of the borehole (2). The external element (4) for contact of the stabilizer (1) with the wall (2a) of the borehole (2) has at least one means for activation (6) of a means (7) co-operating with the wall (2a) of the borehole (2) to limit the friction between the contact element (4) and the wall (2a) of the borehole (2). The activation means can consist of inter-blade spaces (6) for acceleration of the circulation (7) of the drilling liquid or by a means for coupling in rotation of the external element (4) and the central body (3) of the stabilizer (1).

Abstract: A rock drill including a helical shank and a drill head. The drill head has an end face pointing in a feed direction and at least one roof-shaped carbide cutting element on the end face of the rock drill. The carbide cutting element extends transversely across the drill head and has cutting edges. The end face of the carbide cutting element has an additional chip space at least in front of the carbide cutting element and includes an encircling step to create the additional chip space in the feed direction.

Abstract: A portable apparatus for exploration and sampling of placers which is capable of being disassembled for transport into areas not accessible to traditional sampling methods. The sampling unit operates on a principle of power augering and water jetting a sampling pipe to bedrock while concurrently recovering ¾? minus materials, including particles and nuggets of valuable minerals and gemstones, through a concentric center pipe, such recovery powered by a ring jet venturi and supplemented by a sample hole plug to increase the water pressure in the sampling hole.

Abstract: An object of the present invention is to provide a drill bit capable of easily drilling a drill hole that has no rifling, and has high circularity, can be easily positioned, the drill bit comprising a cutting blade tip which is composed of a block body of cemented carbide, three cutting blade portions are formed circumferentially equidistantly around the cutting blade tip, a connection line between a cutting surface 5 and a flank surface 6, said cutting and flank surfaces being formed in each said cutting blade portion 4a, 4b, 4c, acts as a main cutting edge 8 whereas a connection line between a connection surface 7 and said flank surface 6 acts as an auxiliary cutting edge 9, said main cutting edges 8 and said auxiliary cutting edges 9 cross at a blade tip point 10 so that said blade tip point 10 is shaped like a peak with no chisel edge, each said auxiliary cutting edge 9 lies on a line extending from said main cutting edge 8 of a said cutting blade portion located opposite across said blade tip point 10, a

Abstract: A thread coupling for a drill string for percussive drilling has a male thread (5) and a cooperating female thread (4). The male thread is arranged on a first drill string element (3) having a first impact surface (6). The female thread is arranged on a second drill string element (2) having a second impact surface (7). The male and female threads are conical, and the crests (8) of the male thread (5) have a radius of curvature more than thirty degrees of the pitch of the thread.

Abstract: Rotary drilling apparatus comprising at least one kelly bar, interlockable with one ore more other kelly bars in end-to-end arrangement such that, in use, a rotational force applied to an uppermost kelly bar is transmitted to each of the kelly bars below it; a tool, for example an auger, having a bore therethrough in which the outer surface of one of said kelly bars can slideably engage; and lifting means for selectively raising and lowering said tool by sliding it over the outer surface of said kelly bars, whereby, in use, said tool is lowered by sliding it over said interlocked kelly bars and attached to a lowermost kelly bar so that a rotational force applied to said lowermost kelly bar is transmitted to the tool, characterised in that at least part of said lifting means is capable or rotation about a longitudinal axis of said kelly bar for synchronous rotation therewith.

Abstract: A torque absorber is disposed on a drill string near the motor. The torque absorber automatically adjusts the weight on a drill bit and reduces the likelihood of motor stall caused by resistance to drill bit rotation. The torque absorber includes an upper unit assembly and a lower unit assembly. The upper unit assembly includes a top sub and a ball body. The lower unit assembly includes a bottom sub, a lead screw, and a ball retainer. The components of the lower unit assembly are free to rotate as a result of motor back torque, which is in a direction opposite of the direction of rotation of the drill bit during normal drilling. The upper unit assembly will remain stationary while the components of the lower unit assembly rotate in this opposite direction. A spring applies a force on the lead screw, causing the lower unit assembly to rotate back downward once the motor back torque reduces.

Abstract: A masonry or rock drilling tool suitable for use with a rotary hammer has a drilling head (4, 104) at a forward end of the tool. A forwardly extending cutting plate (6, 106) is fitted or formed on the drilling head (4, 104). First and second opposing axially extending channels (36, 38, 136, 138) are formed on the circumferential periphery of the drilling head. The tool has a clamping shank (2, 102) at a rearward end of the tool suitable for fitment within a tool holder of a rotary hammer. An intermediate helical conveying portion (10, 110) extends between the drilling head and the clamping shank. The intermediate helical conveying portion has at least four helically extending flutes (14a-d, 114a-d) separated by corresponding helically extending webs (12a-d, 112a-d). The first of the axially extending channels extend axially rearwardly from a forward facing face of the drilling head into two of the four flutes.

Abstract: A rock drill (1) for rotary hammers or the like is proposed in which a conveying helix (3) having main and secondary webs (6 to 9) is used. In this case, the convexing helix (3) is run up to the front region of the drill head (2) with the core cross section being increased or the flute depth being decreased.

Abstract: A drill for boring an anchor fixing hole 72 having an expanded configuration at a nearby area of a bottom part of the hole, wherein a stopper 4 having a diameter larger than an outside diameter of the drill main body 2 is disposed at a location near a shank 3 of the drill main body 2 and a surface 41 of the stopper 4 on a leading end side of the drill is a tapered curved surface which is expanded towards the shank 3 side from the leading end side of the drill. According to the drill of the present invention for boring an anchor fixing hole, an expanded bottom anchor fixing hole can be bored without using two kinds of drills and at a low cost.

Abstract: A profiled element for rotary drilling equipment and applications to components of a string of drill pipes has an area of abutment on the wall of a drilling hole having a maximum diameter constituting the maximum diameter of the rotary drilling equipment and a turbulence area for producing an activation of the circulation of a drilling fluid in the annulus. The profiled element also has a deflection area adjacent to the abutment area and to the turbulence area, having at least one surface inclined with respect to the axis of the rotary drilling, whose meridian line moves away from the axis in the direction going from bottom to top, in the service position of the profiled element in the drilling hole.

Abstract: A tool for removing solid particles from a well after sand fracturing, drilling, etc. The tool includes a flapper valve assembly above a drill bit, a sand screen, and a screw pump. Fluid in the well, with the solid particles therein, is pumped into the tool by rotating the screw pump, wherein the fluid moves past the bit, across the flapper valve assembly, and through the sand screen. The solid particles stay in a cavity above the flapper valve, but the fluid moves further along the screw pump and is returned along the outside of the tool to the bit, to start the cycle over again. Over time, the cavity fills with solid particles, and the device is raised to the surface, where the accumulated solid particles are dumped. The device can be re-introduced into the well to remove more solid particles, if necessary.

Abstract: A tool for boring has a first shaft for drivingly linking at a first end to a portable rotatable machine. At a second end, the tool has a fastener to which a modular auger section can be drivingly linked. A second shaft of the tool has an outer surface to which a radially inwardly extending edge of a helical flight is attached. A cylindrical collar is attached to a radially outwardly extending peripheral edge of the flight and is mounted radially outwardly of the second shaft. An insulator interposed between the shafts electrically insulates the shafts from each other. The shafts can be unlinked through a shear pin breaking in response to a predetermined amount of relative torque to the shafts.

Abstract: An auger flight support for use with an augering systems for mining which bores a pair of side-by-side holes through the coal seam using respective augers. Each auger includes a drilling section which is followed by a series of auger flights for conveying the bored coal back out of the respective hole. The auger flight support includes a pair of thrust bearing and housing assemblies which are tied together and each supported by a respective leg which lowers the friction between the auger flight and the bottom of the bore. This significantly reduces the power required to rotate the augers.

Abstract: A twist drill bit (1) for use in rock has a helical land (7) arranged between a chuck insert end (2) and a tool head (3), and extends helically around a rotational axis (A) extending along a shaft (5). The radially outer surface (8) of the land (7) has its width (x) increasing as it approaches the tool head (3).

Abstract: A method and apparatus for boring holes in the ground. The apparatus includes an auger translating along a guide. Because the auger translates along the guide, the auger bores a straight hole in the ground. The present invention also contemplates a method. The method of boring holes in the ground includes rectilinearly translating an auger with respect to the ground and boring a hole in the ground with the auger. The method may also include longitudinally and transversely orienting the auger.

Abstract: A hole boring apparatus and method for boring holes in earth is disclosed that includes, a support frame including an earth engaging member and an upright tubular portion adjacent to the earth engaging member so as to provide a passageway therethrough from a top of the tubular portion through the earth engaging member. Also included is a boring member, including a shaft comprising a shaft lower end and a shaft upper end, a blade adjacent to the shaft lower end, a handle adjacent to the shaft upper end, the shaft being located within the passageway of the tubular portion to allow rotation of the shaft, the handle is operational for initiating rotation of the shaft.

Abstract: A method and apparatus for milling a window in a downhole structure, such as a casing or a liner, includes a mandrel that supports milling elements arranged in a predetermined pattern. In one example, the milling elements are arranged in one or more continuous channels each having a generally helical pattern. The milling elements are able to cut the window in the downhole structure substantially continuously to the desired size.

Abstract: A process for producing a pile in the earth with a pipe is provided. The pipe is provided internally with a conduit, which emerges on the bottom side of the pipe, for feeding pile-forming, hardening material into the earth. The pipe is introduced into the earth, and the pipe is removed from the earth while a space created by the removal of the pipe is simultaneously filled with the pipe-forming, hardening material.

Abstract: A tubing shoe (30) comprising: a body (32) for mounting on the end of a tubing string; and reaming members (36) extending longitudinally and helically around the body, the reaming members providing substantially complete circumferential coverage of the body whereby, in use, when the tubing shoe is advanced axially into a bore, the reaming members (36) provide reaming around the shoe circumference. A rotatable torque reducing sleeve or centraliser (38) may also be mounted on the body, rearwardly of the reaming members.

Abstract: A profiled element for rotary drilling equipment and applications to components of a string of drill pipes has an area of abutment on the wall of a drilling hole having a maximum diameter constituting the maximum diameter of the rotary drilling equipment and a turbulence area for producing an activation of the circulation of a drilling fluid in the annulus. The profiled element also has a deflection area adjacent to the abutment area and to the turbulence area, having at least one surface inclined with respect to the axis of the rotary drilling, whose meridian line moves away from the axis in the direction going from bottom to top, in the service position of the profiled element in the drilling hole.

Abstract: A percussion bores for forming borer in a stone material and including a chisel stem (2) having a prismatic cross-section and provided with a chiseling head (3) and at least one radial opening (4), a twist drill (6) extending through the cylindrical through-bore (3) of the chisel stem and projecting beyond the chiseling head (7), a drilling head (10) with cutting elements (9) provided at the projecting end of the twist drill and a shank (12) provided at another end of the twist drill, and a stop (13) provided between the shank (12) and the chisel stem (2), with a drill stem being offset radially inwardly with respect to an outer diameter of the shank in the region of the stop.