Abstract: A rotary drill bit comprises a bit body having a shank for connection to a drill string and a passage for supplying drilling fluid to the face of the bit, which carries a plurality of polycrystalline diamond preform cutting elements. The cutting elements on one side of a diameter of the bit have positive side rake and the cutting elements on the other side of the diameter have negative side rake so that the vectorial sum of the reaction forces between the formation being drilled and the cutting elements provides a resultant lateral imbalance force acting on the bit body as it rotates in use. The gauge of the bit body includes low friction bearing pads so located as to transmit the resultant lateral force to the sides of the borehole. Since the bearing pads are of low friction, they slide around the surface of the formation and any tendency for bit whirl to be initiated is reduced.

Abstract: A rotary drill bit comprises a bit body having a shank for connection to a drill string and a passage for supplying drilling fluid to the face of the bit, which carries a plurality of polycrystalline diamond preform cutting elements. In order to reduce bit whirl, the cutting elements are so disposed as to apply a resultant lateral force to the bit as it rotates during drilling, and the gauge of the bit body is provided with low friction bearing means to transmit said resultant force to the sides of the borehole. Each low friction bearing means includes a roller mounted on the bit body for rotation about an axis parallel to the axis of rotation of the bit, each roller being so disposed that its periphery bears on the formation as the bit rotates.

Abstract: A method of manufacturing a cutter assembly for a rotary drill bit includes the step of bonding to a carrier a cutting element which comprises a thin hard facing layer already bonded to a less hard backing layer, the backing layer having a greater coefficient of thermal expansion than the hard facing layer. In order to compensate for convex deformation of the rear surface of the backing layer, when the cutting element is heated during the bonding process, the rear surface is made initially concave at ambient temperature. Alternatively, or additionally, the co-operating surface of the carrier may be concave.

Abstract: A cutting element for a rotary drill bit comprises a layer of polycrystalline diamond material having a front face and a rear face, a backing layer of less hard material bonded to the rear face of the diamond layer, and a front layer of less hard material bonded to the front face of the diamond layer and extending across at least the major part thereof. The front layer is thinner than the backing layer, at least in the vicinity of the cutting edge of the cutting element.

Abstract: A preform cutting element, for a rotary drill bit, includes a layer of polycrystalline diamond material having a front cutting face, a rear face and a peripheral surface, a cutting edge being provided by at least part of the junction between the front cutting face and the peripheral surface. The diamond layer is formed around its periphery, adjacent the cutting edge, with a row of spaced apertures. Each aperture is in the form of a bore, formed for example by a laser, which is inclined at 45.degree. to the cutting face and extends completely through the diamond layer from the cutting face to the peripheral surface thereof. The apertures serve to inhibit the propagation of spalling across the cutting face from the cutting edge.

Abstract: A cutting structure, for a rotary drill bit, is of the kind comprising a preform cutting element having a front cutting face formed of superhard material, such as polycrystalline diamond, and a rear face bonded to a carrier of less hard material, such as cemented tungsten carbide. The cutting element is bonded to the carrier by means of an alloy having the following composition:Ni about 30% to about 60%Pd about 30% to about 62%Si about 3% to about 15%wherein % is weight percent.An alternative alloy has the following composition:Cr about 4% to about 10%Fe about 1% to about 5%Si about 2% to about 7%C about 0.01% to about 0.10%B about 2% to about 5%Ni Balancewherein % is weight percent.

Abstract: A rotary drill bit is manufactured by forming a main bit body part from a machinable metal, such as steel, machining sockets in the outer surface of the main bit, inserting in each socket a thermally stable cutting structure or former which substantially fills at least the mouth of the socket and projects beyond the outer surface of the main bit body part, applying to the surface of the main bit body part, at least in an area surrounding each socket, a compound comprising powdered matrix-forming material, such as powdered tungsten carbide, mixed with a binder to form a paste, and infiltrating the matrix-forming compound with a metal alloy in a furnace to form a hard matrix. The size, location and orientation of the sockets may thus be accurately determined using conventional machining techniques, as in the case of an ordinary steel-bodied bit, but the external parts of the bit body are formed of hard solid matrix material and are thus highly resistant to erosion.

Abstract: A cutter assembly, for a rotary drill bit, comprises a preform cutting element mounted on a carrier in the form of a stud or post received in a socket in the bit body. The carrier is a metal matrix composite, formed by sintering, hot-pressing or by an infiltration process, and comprising tungsten metal particles in a metal binder phase, or a mixture of tungsten metal particles and tungsten carbide particles in a metal binder phase.

Abstract: A cutting structure for a rotary drill bit includes a cutting element 30 having a front layer 32 formed of polycrystalline diamond, bonded to a backing layer 33 formed of tungsten carbide. The cutting element is bonded to a carrier 33 which is formed of a number of detachable individual elements having means holding them in position such that, upon wear of the cutting structure in use, the holding means of an element engaging the formation will eventually fail, causing detachment of that element from the carrier, and thereby reducing the area of the cutting structure in contact with the formation.

Abstract: In the manufacture of a bit body by a powder metallurgy process, a hollow mold is formed in the configuration of at least a portion of the outer surface of the bit body, and elongate pockets of generally V-section are then formed in the interior surface of the mold, to receive portions of thermally stable cutting elements, each of which is of generally triangular cross-section with a flat front face. Each pocket is machined from the mold material by means of a conical tool rotating about its axis, the axis being inclined to the perpendicular in a plane containing the required longitudinal axis of the pocket. The main elongate part of the pocket is formed by translatory movement of the tool along the axis of the pocket, and a flat, generally triangular, end face is then formed by translatory movement of the tool transversely of the axis of the pocket.

Abstract: There is provided a method of manufacturing a rotary drill bit of the kind including a plurality of cutting structures mounted in sockets in the bit body and projecting from the face of the bit. The method comprises providing a clearance between each cutting structure and its socket and filling the clearance with a settable liquid, the settable liquid being such as to solidify at a temperature less than 400.degree. C. and to retain its integrity, after solidification, at least up to a temperature of 180.degree. C. The solidified liquid acts as a gap filler and provides an interference fit between the cutting structure and the socket. Suitable gap filing settable liquids are: anaerobic adhesive, epoxy resin, dental amalgam, tin/lead solder and bismuth/antimony alloy.

Abstract: A drill bit for drilling deep holes in subsurface formations comprises a bit body having a generally hemispherical leading face and a gauge region, and two blades each extending spirally outwardly across the leading face of the bit body away from the axis of rotation, a cavity of substantial peripheral and axial extent being formed in the bit body on the forward side of each blade, and communicating with an associated exit channel in the gauge region. A plurality of cutting elements are mounted along each blade, the cutting elements being mounted closely adjacent one another side-by-side along the blade so that their cutting edges together form a single long cutting edge without substantial discontinuities. A passage in the bit body supplies drilling fluid to nozzles in the cavities for cooling and cleaning the cutting elements, fluid from the nozzles sweeping past the cutting elements and out through the exit channels.

Abstract: A rotary drill bit for use in drilling or coring deep holes in subsurface formations comprises a bit body having a leading face and a gauge region, cutting elements mounted at the leading face of the bit body, and a passage in the bit body communicating with nozzles in the leading face of the bit body for supplying drilling fluid to the face for cooling and cleaning the cutting elements. Certain of the cutting elements each comprise a preform cutting element having a superhard front cutting face providing a cutting edge, and others of the cutting elements each comprise particles of hard material embedded in a front layer of a less hard material to form a cutting layer having a cutting edge.