Abstract: A clamp for a downhole tool includes a sleeve having an axis and sleeve bodies. The sleeve bodies are coupled together on a first side of the clamp. Fasteners are used to mechanically lock the sleeve bodies together on a second side of the clamp to surround and clamp onto an exterior of a drill string having pipes. The pipes are coupled together at their coupled connections. In addition, recesses are formed in an exterior of each sleeve body. Inserts are mounted in the recesses to provide low friction exterior surfaces for the clamp.

Abstract: Provided is an anti-rotation system and method of operating a downhole tool. The anti-rotation system, in one embodiment, includes a housing defining a longitudinal axis, and a carriage mounted within the housing, the carriage including at least one anti-rotation blade configured to engage a formation and resist rotation of the housing about the longitudinal axis. The carriage, in accordance with this embodiment, is configured to rotate about a carriage axis and tilt the at least one anti-rotation blade from a first extended position to a second at least partially retracted position.

Abstract: A downhole drilling apparatus may comprise a rotatable body with fixed cutting elements protruding from an exterior thereof. To form a subterranean borehole, the fixed cutting elements, spaced at a constant radius from a rotational axis of the body, may degrade an earthen formation as the body rotates. The body may also have a rotatable cutting element protruding from its exterior. To remove material from an interior wall of the borehole, the rotatable cutting element may be positioned in a first rotational orientation wherein it extends radially beyond the constant radius of the fixed cutting elements. An amount of material being removed may be altered by rotating the rotatable cutting element into a second rotational orientation wherein it remains radially within the constant radius.

Abstract: An anchor activation system including a housing having an outer surface, an inner surface defining an internal chamber, a first end, and a second end. A slip is shiftably mounted to the outer surface of the housing. The anchor activation system also includes a piston assembly and an activator mounted to the piston assembly. The activator selectively shifts the slip axially along the housing. A biasing member is arranged between the second end and the activator. A trigger is operable to selectively release the piston assembly.

Abstract: A downhole, hydraulically actuated drilling stabilizer provides versatility in a bottom-hole assembly. The drilling stabilizer can be used in a directional drilling application to help control the inclination in an extended reach or horizontal well. The drilling stabilizer has stabilizer blade members with an angular design portion that provides versatility in a bottom-hole assembly. The stabilizer can also be used in a conventional rotary bottom-hole assembly or positioned below a steerable motor. A drilling stabilizer with adjustable extension diameters provides improved inclination control over currently existing options.

Abstract: A wear pad for a drill pipe body of downhole drilling assembly comprising at least one wear insert and a wear pad material that at least partially encases the at least one wear insert. The wear inserts can be supported by or attached to an insert support structure of the drill pipe body. The insert support structure and the wear inserts can be welded over by the wear pad material to at least partially encase the wear inserts (e.g., using a plasma transfer arc welding tool). The wear inserts can comprise tungsten carbide impregnated with industrial diamonds, and the wear pad material can comprise tungsten carbide, the wear inserts comprising an overall hardness greater than the hardness of the wear pad material. A second wear pad can be formed adjacent to, and have similar features as, the wear pad. The wear pads can be separated by or located on opposite sides of a bend portion of a bent housing drill assembly.

Abstract: A completions bit for use in a wellbore includes: a shank having a coupling formed at an upper end thereof; a body mounted to a lower end of the shank; and a cutting face forming a lower end of the bit. The cutting face includes: a blade protruding from the body; a tangentially oriented leading cutter mounted to a bearing face of the blade adjacent to a leading edge of the blade at an inner portion of the cutting face; and a radially oriented leading cutter mounted to the bearing face of the blade in proximity to the leading edge thereof at an outer portion of the cutting face.

Abstract: A method includes determining a first geometric parameter of an elastic component based on a second geometric parameter of the elastic component, wherein the elastic component is part of a bottomhole assembly having a bit and an eccentering mechanism operating on the elastic component. The method also includes determining a length difference of the elastic component based on the first geometric parameter, the second geometric parameter, and a stiffness factor of the elastic component. The method also includes determining a borehole curvature based on a sum of a bit tilt angle and a force-based side-cutting angle, wherein the force-based side-cutting angle is based on the length difference of the elastic component. The method also includes determining a setting of the eccentering mechanism based on the borehole curvature.

Abstract: A drilling apparatus may alter a direction of travel of a drill bit as it forms a borehole in the earth by furnishing the borehole with a cross-sectional shape that urges the drill bit in a radial direction. Such a cross-sectional shape may comprise two circular arcs, one larger than the apparatus and one smaller. The apparatus may be urged away from the smaller circular arc and into the open space provided by the larger circular arc. Such an apparatus may comprise an axial body and a cutting element extendable in a single radial direction from an exterior of the axial body. Extension of the cutting element may allow it to engage and degrade an inner wall of the borehole. An abrasion-resistant gauge pad protruding from the exterior of the body may ride against the borehole wall and urge the body radially.

Abstract: A device to protect a structural member against a cutting threat, such as a saw blade or thermal cutting device, is provided. The device provides a substrate having a cavity disposed therein. A cutting resistant element is disposed within the cavity to impede cutting of a cutting device, such as a saw blade or thermal cutting device, into the cutting resistant element.

Abstract: Reamer for earth-boring applications may include a body having a longitudinal axis and a blade carried by the body. The blade may include at least one cutting element located at a first radial distance from the longitudinal axis and a gage pad located at a second, smaller radial distance from the longitudinal axis. Methods of enlarging pilot holes in earth formations utilizing reamers may involve removing earth material from a sidewall of the pilot hole utilizing at least one cutting element located at a first radial distance from a longitudinal axis of a body of the reamer on a blade of a reamer. The reamer may be stabilized by placing a gage pad located on the blade in sliding contact with a portion of the sidewall of the pilot hole, the gage pad located at a second, smaller radial distance from the longitudinal axis.

Abstract: A stabilizer device is provided for a mud motor drilling assembly. The stabilizer device may be mounted to a motor housing having one or more grooves or ridges. The stabilizer device may include a stabilizer body, a threader portion, and a clamp. The threaded portion may be positioned between the one or more grooves or ridges and the clamp. The threaded portion may include an external surface having threads. The threads on the external surface of the threaded portion of the stabilizer device may correspond to threads on an internal surface of a clamp. The threaded coupling of the clamp to the stabilizer device may couple the stabilizer device to the motor housing at the one or more grooves or ridges.

Abstract: A drilling string stabilizer tool comprises a cylindrical body and a plurality of stabilizer blades mounted on the outer surface of the cylindrical body. The stabilizer blades have an elongated shape and a monolithic structure with an upper stabilizing part and a lower mounting part. Between each two adjacent blades there can optionally be a hydrodynamic flute for improving the flow of liquid and cuttings during drilling and tripping.

Abstract: This invention relates to an articulating component (16) of a downhole assembly, and to a downhole steering assembly. There is provided an articulating component (16) having a first end (40) and a second end (42), the articulating component being adapted to transmit torque between the first end and the second end. The articulating component has a pivotable coupling (46) between its first and second ends and at least one control element for the pivotable coupling, the control element(s) having an active condition in which the pivotable coupling is substantially locked against pivoting movement, and an inactive condition in which the pivotable coupling is unlocked. In a downhole steering assembly the articulating component is located downhole of the steering component whereby to protect the steering component from unwanted vibrations generated downhole, or uphole of the steering component whereby to protect the steering component from unwanted vibrations generated uphole, or both.

Abstract: A drill bit for use in a wellbore is disclosed, including a bit body having a longitudinal axis; and at least one moveable member associated with a lateral extent of the bit body, wherein the at least one moveable member is configured to translate in a member axis that is substantially longitudinal. Further, a method of drilling a wellbore is disclosed, including providing a drill bit including a bit body having a longitudinal axis and at least one movable member associated with a lateral extent of the bit body; conveying a drill string into a formation, the drill string having the drill bit at the end thereof; drilling the wellbore using the drill string; and selectively translating at least one movable member in a member axis that is substantially longitudinal.

Abstract: A bidirectional stabilizer which reduces impact damage while rotating into and out of a wellbore. The bidirectional stabilizer can be coupled on a first end to a drill string and on a second end to a drill bit. The bidirectional stabilizer can have an annulus configured for maximum wellbore fluid flow. A cutting portion can be formed on a shaft with a plurality of helical blades between the first shaft end and the second shaft end. The plurality of helical blades of the cutting portion can be on a first plane and a plurality of cutting nodes can be on a second plane for smoothing a wellbore. The plurality of cutting nodes can have at least one impact arrestor mounted directly adjacent each cutting node.

Abstract: A bidirectional stabilizer, which reduces impact damage while rotating into and out of a wellbore. The bidirectional stabilizer can be coupled on a first end to a drill string and on a second end to a drill bit. The bidirectional stabilizer can have an annulus configured for maximum wellbore fluid flow. A cutting portion can be formed on a shaft with a plurality of blades between the first shaft end and the second shaft end. The plurality of blades of the cutting portion can be on a first plane and a plurality of cutting nodes can be on a second plane for smoothing a wellbore. The plurality of blades can have a wrap angle for forming a particle flow path between pairs of the plurality of blades configured with a line of sight parallel to the longitudinal axis.

Abstract: A method, system and apparatus for steering a drill string and including an eccentric steering device. The eccentric steering device may comprise an eccentric sleeve configured for mounting exterior to a portion of the drill string and permitting the drill string to rotate within the eccentric sleeve and a brake positioned to selectively cause rotation of the eccentric sleeve with the drill string. In one embodiment, the eccentric steering device may further comprise one or more bearings positioned between the eccentric sleeve and the drill string.

Abstract: A drilling system that includes a bit body that has a longitudinal axis, a blade of a selected length on a side of the bit body and substantially along the longitudinal axis, and a movable member associated with the blade that extends from a retracted position to a selected extended position along the longitudinal axis, thereby effectively extending the length of the blade when the movable member is in the selected extended position.

Abstract: An attachable collar arrangement for a down hole apparatus that includes a collar member releasably insertable into a cutaway section disposed circumferentially around a tool joint or other down hole apparatus. The collar member is stabilized in position within the cutaway section by means of a stabilizing insert member which is releasably inserted between at least two sections of the collar member, and removably secured into a member insert receptacle disposed upon the tool joint or other down hole apparatus. Wear and erosion are directed to the collar member during drilling operations and the tool joint or down hole apparatus is thereby protected. The collar member is expediently replaceable when needed and drilling operations are extended over the life of particular drilling equipment to which the device is installed.

Abstract: A setting tool for use inside a well bore casing having an upper portion, a lower portion, and a wrap spring. The upper portion includes a mandrel coupled to a connecting line. The upper portion is configured to receive an input. The lower portion includes a first sleeve configured translate along an axis of the setting tool. The lower portion is selectively coupled to the upper portion. The wrap spring has a torsional preload and is coupled to the upper portion and the lower portion. The wrap spring is configured to selectively release the lower portion and upon reception of the input, such that the first sleeve is permitted to translate along the axis.

Abstract: A plunger assembly arranged to minimize uneven wear spots thereon during the plunger assembly's horizontal and vertical travel within a hydrocarbon producing well conduit. The plunger assembly comprises an elongated central mandrel having a bore extending longitudinally therethrough for transmitting gaseous fluids from a well, through the plunger assembly, a pair of longitudinally spaced-apart sets of arcuately shaped wear pads guidably supported on outer portions of the elongated central mandrel, and at least one tangentially directed nozzle arranged to direct gaseous fluids from the bore of the elongated central mandrel against an inner side of at least one of the arcuately shaped wear pads arranged on the outer portions of the elongated central mandrel.

Abstract: The present invention relates a high-strength nonmagnetic stainless steel, containing, by weight percent, 0.01 to 0.06% of C, 0.10 to 0.50% of Si, 20.5 to 24.5% of Mn, 0.040% or less of P, 0.010% or less of S, 3.1 to 6.0% of Ni, 0.10 to 0.80% of Cu, 20.5 to 24.5% of Cr, 0.10 to 1.50% of Mo, 0.0010 to 0.0050% of B, 0.010% or less of O, 0.65 to 0.90% of N, and the remainder being Fe and inevitable impurities; the steel satisfying the following formulae (1) to (4): [Cr]+3.3×[Mo]+16×[N]?30??(1), {Ni}/{Cr}?0.15??(2), 2.0?[Ni]/[Mo]?30.0??(3), and [C]×1000/[Cr]?2.5??(4), wherein [Cr], [Mo], [N], [Ni], [Mo] and [C] represent the content of Cr, the content of Mo, the content of N, the content of Ni, the content of Mo and the content of C in the steel, respectively, and {Ni} represents the sum of [Ni], [Cu] and [N], and {Cr} represents the sum of [Cr] and [Mo]. The present invention further relates to a high-strength nonmagnetic stainless steel part containing the steel and a process for producing the same.

Abstract: A cleaning tool (1) for use in cleaning ferrous material from a wellbore has a magnetic cleaning element (14) mounted to a tool body (2) within a slot (5) using a releasable concealed interference fit fastener assembly (15) comprising a fastener member having a head (16), and a shank (17) with a configured end (18) and a deformable fastener ring (20) adapted to fit closely over the shank, and a press-fit collar (21) adapted to deform the deformable fastener ring upon the configured end of the shank when assembled, and wherein the respective head and collar are each flanged to permit an interference fit with a corresponding contact surface of the tool body around said slot.

Abstract: Magnetic retrieval tools for use in a wellbore or other tubular member to remove metallic debris. A magnetic retrieval tool includes a tool body having a central shaft with a plurality of ribs that project radially outwardly therefrom. The ribs present lateral sides that have recesses formed therein. Magnet bars are retained within the recesses by wedge members and retaining rings. The magnet bars include a hollow protective housing that encloses a plurality of magnets. Retaining plugs are used to secure the magnets within the housing.

Abstract: A method and system for cementing a tubular and mud motor in a wellbore utilizing burst disks above the mud motor. The burst disks rupture to permit the cement to flow through the burst disks and bypass the mud motor. All of the burst disks reliably rupture at a predetermined and known threshold pressure so as to permit cement to be pumped at a desired rate through all of the ruptured burst disks. Each burst disk is provided with a cover for maintaining a chamber of a known pressure between the cap and the burst disk. All of the burst disks predictably and reliably rupture at the rated pressure.

Abstract: A downhole assembly for insertion into a borehole comprising an articulated mandrel, a passive and an active damping mechanism operating on said mandrel for exercising control over torsional stick-slip and further proposing an improvement over the prior art which diminishes lateral shock.

Abstract: Apparatus and methods for securement of lines to downhole well tools. A method of securing one or more lines to a well tool includes the steps of: installing the one or more lines in a groove formed longitudinally along an outer surface of the well tool, the groove having a width at the outer surface of the well tool which is narrower than a width of the groove at a position radially inward relative to the outer surface; and securing the one or more lines in the groove. A well tool includes a groove formed longitudinally along an outer surface of an outer housing of the well tool. The groove has a width at the outer surface of the well tool which is narrower than a width of the groove at a position radially inward relative to the outer surface. One or more lines are secured in the groove.

Abstract: A blade for a stabilizer configured with a compound engagement profile for reducing a tendency toward whirl and other vibrational effects when rotated within a borehole of a subterranean formation is provided. A method for stabilizing down-hole components is also provided.

Abstract: A turbine matrix sleeve in accordance with the invention includes an inner cylindrical structure made up of a first material. The inner cylindrical structure may include multiple blades and multiple channels running between the blades along an outside diameter thereof. The inner cylindrical structure further includes threads, such as right-hand or left-hand threads, on an outer surface thereof. An outer layer, made up of a second material different from the first material, is integrally bonded to the threads. This outer layer may be optionally embedded with hardened inserts or buttons, such as PDC inserts, diamond inserts, TSP inserts, or the like. The threaded surface on the inner cylindrical structure significantly improves the bond between the outer layer and the inner cylindrical structure and creates a mechanical lock therebetween.

Abstract: An adjustable centering tool for use in pipes of varying inner diameter. The centering tool being provided with a number of identical and steplessly adjustable, radially protruding wings having guiding lugs and chamfered end faces. The wings, having been set, are retained by an upper lock mandrel with a safety pin and a lower lock mandrel with a safety nut. The outer circumference of a cylindrical tool body is fitted with longitudinal grooves having sloped terminations cooperating with the wing dimensions, the chamfered end faces of the wings, and the guiding lugs.

Abstract: A turbine matrix sleeve in accordance with the invention includes an inner cylindrical structure made up of a first material. The inner cylindrical structure may include multiple blades and multiple channels running between the blades along an outside diameter thereof. The inner cylindrical structure further includes threads, such as right-hand or left-hand threads, on an outer surface thereof. An outer layer, made up of a second material different from the first material, is integrally bonded to the threads. This outer layer may be optionally embedded with hardened inserts or buttons, such as PDC inserts, diamond inserts, TSP inserts, or the like. The threaded surface on the inner cylindrical structure significantly improves the bond between the outer layer and the inner cylindrical structure and creates a mechanical lock therebetween.

Abstract: A drilling stabilization system includes a power section coupled to an upper end of a transmission housing, a bearing housing coupled to a lower end of the transmission housing, and a drill bit coupled to the bearing housing, wherein the transmission housing includes at least two radially outwardly extending blades disposed on the transmission housing. A method of drilling a substantially concentric wellbore includes drilling a formation with a directional drilling bottomhole assembly coupled to a drill string, changing a direction of the drilling of the formation being drilled, removing the directional drilling bottomhole assembly from the drill string, coupling a drilling stabilization system to the drill string, and drilling the formation with the drilling stabilization system.

Abstract: An apparatus for protecting a sub assembly inside a borehole of a well, with a sleeve having a sleeve outer diameter larger than the body outer diameter; a plurality of offset indentations formed on the outer side of the sleeve formed in rows of 4 to 8 offset indentations along a diagonal orientation to a sleeve axis; a plurality of a metal carbide inserts providing an interference fit into each offset indentation thereby forming a wear resistant pad on the outer side of the sleeve; a sealing means disposed between the sleeve bottom beveled edge and the body forming a sealed sub assembly using at least two spring locking apparatus engaging locking indentations on the body.

Abstract: The present invention relates to an adjustable centering tool (1) for use in pipes of varying inner diameter, said centering tool (1) being provided with a number of identical and steplessly adjustable, radially protruding wings (2) having guiding lugs (2?) and chamfered end faces (2?). The invention is characterized in that the wings (2), having been set, are retained by an upper lock mandrel (3) with a safety pin (4) and a lower lock mandrel (5) with a safety nut (6), the outer circumference of a cylindrical tool body (7) being fitted with longitudinal grooves (8) having sloped terminations (8X) cooperating with the wing dimensions, the chamfered end faces (2?) of the wings (2), and the guiding lugs (2?), respectively.

Abstract: The invention is an attachment means for a ground drilling or cutting tool (10) that enables cutting elements (11) to be removably secured to the tool (10). The attachment means include a first surface (13) on the cutting element (11), a second surface (14) on the tool (10) upon which the first surface (11) locates, dowel holes (15) in each of the first and second surfaces, dowels (16) that locate in aligned dowel holes between said surfaces, engagement surfaces (17, 18) on the cutting element and tool that extends substantially parallel to the longitudinal axis of the tool and engage to resist side loads applied to the cutting elements (11) and fastening means (19) that secures the cutting elements (11) to the tool (10). The invention provides a means of easily removing the cutting elements (11) from the tool (10) for either replacement or maintenance work.

Abstract: Disclosed drilling systems offer multiple methods providing access to the open borehole without first tripping the drill string. In some embodiments, a drill bit has a tool port that is blocked by a plug during normal drilling operations. When a tool is deployed through the interior of the drill string, the tool port opens, enabling the tool to enter the borehole beneath the drill string and perform logging or sampling operations. The plug may be attached to the drill bit by a hinge or pivot, or alternatively, the plug may be discarded and a replacement seated in place after the tool is retracted into the drill string. In other embodiments, the drill bit itself is detachable, allowing the bit to be parked in the hole or in a side bore. If desired, the bit can be re-attached by lowering the drill string to the bottom of the hole.

Abstract: A roller sub system for reducing friction between a tool string and a wall in a well bore for use in the oil and gas industry. The apparatus has a roller body and wheel sub system, which is configured to have removably mounted wheels of variable diameters. A plurality of different diameter wheel sets are described for mounting on the roller sub axles and orientating the system in the well bore. The wheels are fixed to the roller sub axles through a quick-release mechanism. A single apparatus can thus be employed with different diameter wheels to operate in well bores of variable diameters.

Abstract: A variable gauge drilling apparatus and a method for assembling a variable gauge drilling apparatus for insertion in a subject borehole. The variable gauge drilling apparatus includes: an apparatus housing having a housing size which is suitable for insertion in a subject borehole which has a subject borehole size within a design range of borehole sizes; a plurality of interchangeable borehole engaging devices having different device sizes for mounting on the apparatus housing to provide the drilling apparatus with a drilling apparatus size within a range of drilling apparatus sizes, wherein the range of drilling apparatus sizes is compatible for use of the drilling apparatus within the design range of borehole sizes; and a universal borehole engaging device mount located on the apparatus housing, wherein the mount is configured to accept for mounting any one of the plurality of interchangeable borehole engaging devices.

Abstract: A multi-unit centralizer for centralizing or otherwise positioning a tubing string in a well bore. The centralizer has a centralizer hub including multiple hub subunits for removably engaging each other and at least one spacer lug for removably engaging each of the hub subunits.

Abstract: The invention is a method and apparatus for determining an electrical property a formation surrounding a borehole with a measuring-while-drilling device. The apparatus an antenna configuration disposed along the outer face of an extendable stabilizer joined to a rotatable drill collar. Typically, two receivers and two transmitters are spaced along the longitudinal axis of the drill collar, with the two receivers spaced symmetrically in between the two transmitters. Alternatively, receivers and transmitters can be spaced along the circumference, possibly over multiple stabilizers. Multiple assemblies can be used. Data can be obtained with the transmitter-receiver assembly held in a stationary position or rotating circumferentially. Apparatus can be operated in a “broadside” configuration, an “endfire” configuration, or a configuration in which transmitter coils and receiver coils are oriented orthogonally to each other.

Abstract: An instrument insert for a tool of the type comprising an inner member extending within an outer member, the inner and outer members being capable of relative longitudinal movement. The insert includes a first insert portion comprising a first instrument component of an instrument, a second insert portion comprising a second instrument component of the instrument and a coupling mechanism for connecting the first and second insert portions and for maintaining the first and second insert portions in a fixed relative longitudinal position. Further, the first and second insert portions are each adapted to be connected with one of the inner and outer members and the insert is adapted for mounting within the tool at a radial position between the inner and outer members such that the insert is capable of longitudinal movement relative to at least one of the inner and outer members.

Abstract: A well borehole is prevented from deviating from its intended vertical path as it is being drilled by use of a sub assembly which is eccentrically weighted with respect to its axis of rotation. Such a sub assembly can comprise a straight tubular member weight relieved along one side by, for example, forming a cavity within the heavy walls of the tubular member along the side of the collar. Thus, the eccentric weight is imposed upon the drill bit without providing any protrusions or elbows which are designed to bear on the wall of the borehole. Additionally, as the cavity is contained within the heavy walls of the tubular member, drilling fluids containing various debris cannot inhabit the cavity, thus maintaining a constant eccentric weight upon the drill bit.

Abstract: The present invention provides a roller sub for use downhole in oil or gas wells as part of a toolstring or drill string to reduce friction between the string and wellbore. The roller sub is a modular assembly of parts which assemble together to trap the roller wheels in place between them, avoiding need for grub screws to fasten the individual wheels and rendering the roller sub very compact.

Abstract: The present invention is for a drill string stabiliser tool (18) used in borehole drilling. The tool includes a symmetrical body (20) with a plurality of external recesses (22). The recesses (22) have internal opposite surfaces (23) which converge inwardly from the outer surface of the body. A pad assembly (24) is disposed in each recess (22) and includes a wedge block (28) with converging radially inwardly opposite side surface (29) complementarily abutting said recess surfaces. Each wedge block (28) has a bolt (30) securing said wedge block (28) to said body (20) and is slightly larger dimensioned than the recess (22). The angles of the wedge blocks and the recesses are so chosen to effect an interference fit so that when the wedge block (28) is forced into the recess (22) by use of the bolt (30) it is held there by an interference fit.

Abstract: A down-hole tool for use in an oil or gas well is provided with detachable components that are held to a body or tool housing by longitudinal mechanical fasteners disposed in a generally radial orientation. The mechanical fasteners allow for the components to be quickly removed and refurbished or replaced, while also permitting radial movement or floating of the components during operation of the tool. A spring may be incorporated to bias the components in a radial outward direction during operation.

Abstract: A cutting bed impeller comprises a body portion and a plurality of paddles projecting outwardly from the body portion, at least one of the paddles comprising a radially outer face extending between a leading edge and a trailing edge in a normal direction of rotation of the impeller about an axis of rotation of the cutting bed impeller, a leading face, and a trailing face. The radially outer face extends between the leading face and the trailing face. The leading face is inclined at a first angle &agr; to a first tangent T1 to the radially outer face at the leading edge. The trailing face is inclined at a second angle &bgr; to a second tangent T2 to the radially outer face at the trailing edge, the second angle &bgr; being less than the first angle. The radially outer face of one or more of the paddles may be provided with one or more replaceable wear elements.