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 preform cutting element for a rotary drill bit includes a layer of polycrystalline diamond material, the rear face of which is bonded to the front face of a backing layer of less hard material, such as tungsten carbide. The rear face of the backing layer is substantially greater in area than the rear face of the diamond layer. A method of manufacturing such cutting elements comprises forming an intermediate structure comprising polycrystalline diamond material bonded between two outer layers of tungsten carbide, and then cutting the intermediate structure to provide two pieces, each of the pieces including part of the diamond material and at least a major part of a respective one of the two outer layers.

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 rotary drill bit for use in drilling holes in subsurface earth formations comprises a bit body having a shank at one end for connection to a drill string and an operating end face at the other end. A plurality of first cutting structures, each comprising a preform cutting element, is mounted in the bit body at the end face thereof, and each has a superhard front cutting face. The bit body includes a plurality of protuberances projecting outwardly from the adjacent portions of the end face, the protuberances forming a plurality of second cutting structures disposed in generally trailing relation, respectively, to at least some of the first cutting structures. Each of the protuberances is impregnated with superhard particles through a significant depth measured from the outermost extremity of the protuberance.

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 roller cutter (28) for a rotary drill bit (10) and method of making, utilizing an ion nitriding hardening process for the external surface (42) and the internal bearing surfaces (33, 34, 38) in the central cavity (30) of the roller cutter (28). The roller cutter (28) is made from a through hardenable steel and the ion nitrided hardened layer (77) has a total thickness less than around 0.030 inch. Hardened layer (77) has a relatively thick inner stratum (80) and a relatively thin outer surface stratum (78). The outer stratum (78) is formed of Fe.sub.4 N having a thickness no greater than around 0.0004 inch to form an outer surface which is ductile and has a relatively low friction coefficient.

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 rotary drill bit for use in drilling or coring holes in subsurface formations comprises a bit body having a shank for connection to a drill string, a plurality of cutter assemblies mounted at the surface of the bit body, and a passage in the bit body for supplying drilling fluid to the surface of the bit body for cooling and cleaning the cutter assemblies. At least some of the cutter assemblies each comprise a cutting element on a stud which is recveived in a socket in the bit body, the centerline of the stud being disposed at an angle to the normal direction of forward movement of the cutter assembly in use of the bit. At least three of such cutter assemblies are disposed closely adjacent one another in a row, adjacent cutter assemblies in the row having their centerlines inclined at different angles to allow closer packing of the cutter assemblies.

Abstract: A rotary drill bit (10) having a plurality of roller cutters (20) with rows (32A, 32B, 32C, 32D) of cutting inserts (34,36,38,40) mounted within sockets (35,46) on the frusto-conical cutter body (30). The cutting inserts 34,36,38,40) have cutting surfaces formed with a wear-resistant material with certain cutting inserts (36,38) being formed of a wear-resistant material having a hardness higher than the hardness of the wear-resistant material on the remaining inserts (34,40) in each row. The hard cutting inserts (36,38) are positioned in each row in a predetermined pattern intermingled in a generally uniformly spaced pattern with the softer cutting inserts (34,40) and comprising generally between 20% and 50% of the total number of cutting inserts in a particular row.

Abstract: A rotary drill bit for use in drilling or coring holes in subsurface formations comprises a bit body having a shank for connection to a drill string, a plurality of cutting structures mounted at the surface of the bit body, and a passage in the bit body for supplying drilling fluid to the surface of the bit body for cooling and/or cleaning the cutting structures. The bit body is formed from steel, and each cutting structure comprises a cutting element, in the form of a unitary layer of thermally stable polycrystalline diamond material, brazed to a carrier received in a socket in the steel body of the bit.

Abstract: A roller cutter (28) of a drill bit (10) is retained on a journal (24) for rotation by a retainer ring (82) having external screw threads (88) which are threaded onto mating screw threads (108) on the roller cutter (28) for rotation therewith. The retainer ring (82) is mounted within a semicircular groove (68) on the journal (24) and has an inner periphery formed of a smooth arcuate surface contacting the annular groove at a position spaced at least 10.degree. from the entrance opening of the groove thereby to reduce bending stresses exerted against the root (74) of the groove (68).

Abstract: A drag type drill bit (10) having a plurality of solid block-like holders (30, 32, 34) secured to and projecting from the bit body (12), each holder (30) having a plurality of cutting elements (36) thereon defining spaced cutting edges 54. Each cutting element (36) has a planar cutting face (46) and a cutting edge (54) extending along the cutting face (46) with the cutting face (46) extending in a generally radial direction with respect to the axis of rotation of the bit (10). The holders (30, 32, 34) are arranged in a plurality of rows extending outwardly from adjacent the axis of rotation of the drill bit (10) and the holders (30, 32, 34) in each row are staggered rearwardly with respect to the direction of rotation.

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: A rolling cutter (24) for a rotary drill bit (10) having cutting inserts or elements (52) mounted within sockets (54) in a so-called full shrink process. The rolling cutter (24) is heated to a temperature over around 500.degree. F. in a controlled inert atomsphere in an enclosed heat chamber (71) and the inserts (52) are positioned by gravity within the sockets (54) in a slip fit for retention in an interference fit by shrinkage of the cutter body (25).

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.