Abstract: A cutting element, for a rotary drill bit, comprises a tablet having a front face, a rear face and a peripheral edge, at least the front face of the tablet being provided by a layer of superhard material, such as polycrystalline diamond. The peripheral edge of the tablet is formed with one or more re-entrant portions so as to define projecting cutting portions to the sides of the re-entrant portions. The element may be cut from a blank which is initially circular.

Abstract: A rotary drill bit for use in drilling or coring deep holes in subsurface formations comprises a bit body having a shank for connection to a drill string and a plurality of cutting elements mounted at the surface of the bit body. Each cutting element is bonded to a stud which is received in a socket in the bit body. Spaced rearwardly of each cutting element is a separate abrasion element comprising a stud which is received in a socket in the bit body and is impregnated with particles of natural or synthetic diamond. The abrasion element provides a back-up in the event of failure or excessive wear of the cutting element and its spacing from the cutting element prevents the damaging transfer of heat from the abrasion element to the cutting element. The cooling may be enhanced by providing a channel for drilling fluid between the cutting element and abrasion element.

Abstract: The body of a rotary drill bit is formed from a matrix formed by a powder metallurgy process, and a plurality of cutting elements are mounted on the bit body, each cutting element being in the form of a disc of superhard material which is thermally stable at the temperature of formation of the matrix. The front surface of each cutting element is engaged by a holding structure on the bit body in front of the cutting element, the arrangement of the holding structure being such that the resistance provided by the holding structure to forward deflection of the portion of the cutting element opposite the cutting edge is less than the resistance to rearward deflection provided by the surface behind the cutting edge. Bending stresses imparted to the cutting element by rearward deflection thereof in the vicinity of the cutting edge are thereby reduced.

Abstract: A rotary drill bit for use in coring holes in subsurface formations comprises a bit body having a shank for connection to a core barrel, an outer peripheral gauge portion for engagement with the peripheral wall of the hole being drilled, an inner peripheral gauge portion defining at least a part of a central, generally circular aperture extending axially through the bit body, a plurality of cutting elements mounted at the surface of the bit body, and passages in the bit body for delivering drilling fluid to the surface of the bit body. Hydraulic sealing means are provided on the inner gauge portion of the bit and, in use, engage the outer surface of the core being cut by the bit. The hydraulic seal thus formed prevents or restricts flow of drilling fluid in an axial direction between the inner gauge portion and the core, and thus substantially reduces erosion of the core.

Abstract: A method of forming a cutting structure for a rotary drill bit comprises brazing a thermally stable polycrystalline diamond cutting element to a carrier, the carrier being formed of a material such that, at the brazing temperature, the difference in coefficient of thermal expansion between said material and the polycrystalline diamond material is less than the difference in coefficient of thermal expansion between tungsten carbide and the polycrystalline diamond material. A suitable carrier material is silicon carbide.

Abstract: A method of manufacturing a rotary drill bit of the kind comprising a bit body having a shank for connection to a drill string, a plurality of cutting structures mounted in sockets in the bit body, and a number of nozzles also mounted in sockets in the bit body and communicating with a passage for supplying drilling fluid to the face of the bit. The method includes the steps of forming at least part of the bit body from steel, forming the sockets in the bit body part, plugging each socket with a former which projects partly beyond the bit face, applying to the bit face a coating of a fusible hardfacing material, heating the coated bit body part so as to fuse the hardfacing material, cooling the bit body part to solidify the fused hardfacing material, and then removing the formers from the sockets.

Abstract: A rotary drill bit comprises a bit body having a leading face and a gauge region, a number of blades on the leading face of the bit body, and a number of cutting elements mounted along each blade. A passage in the bit body supplies drilling fluid to nozzles in the leading face of the bit body for cooling and cleaning the cutting elements. Each nozzle is so oriented, and the surface of the bit body in the region in front of each blade is so shaped, as to promote a vortex flow of drilling fluid around said region, with part of the periphery of the vortex extending across the cutting elements on the blade, so that fluid in the periphery of the vortex passes across the cutting elements mounted on each blade before escaping through an exit channel in the gauge region.

Abstract: A method of manufacturing by a powder metallurgy process a rotary drill bit including a bit body having an external surface on which cutting elements are mounted, and a passage for supplying drilling fluid to the surface of the bit. The method comprises forming a hollow mould for moulding at least a portion of the bit body, packing at least part of the mould with powdered matrix material, and infiltrating the material with a metal alloy in a furnace to form a matrix. Before the mould is packed with the powdered material, formers are positioned on the interior surface of the mould to project into the interior of the mould space and form sockets to receive nozzles, or studs on which the cutting elements are mounted. According to the invention, the formers are formed from material, such as austenitic stainless steel, having a coefficient of thermal expansion not less than that of the matrix material.

Abstract: A rotary drill bit for use in drilling or coring deep holes in subsurface formations comprises a bit body having a shank for connection to a drill string and a plurality of cutting elements mounted at the surface of the bit body. Each cutting element is bonded to a stud which is received in a socket in the bit body. Spaced rearwardly of each cutting element is a separate abrasion element comprising a stud which is received in a socket in the bit body and is impregnated with particles of natural or synthetic diamond. The abrasion element provides a back-up in the event of failure or excessive wear of the cutting element and its spacing from the cutting element prevents the damaging transfer of heat from the abrasion element to the cutting element. The cooling may be enhanced by providing a channel for drilling fluid between the cutting element and abrasion element.

Abstract: A cutter assembly, for a rotary drill bit, comprises a generally cylindrical stud to be received in a socket in the surface of the bit body, the stud being formed, adjacent one end thereof, with a plane surface inclined at an angle of less than 90.degree. to the longitudinal axis of the stud, and a preform cutting element mounted on the inclined surface. The dimensions of the cutting element, and its location on the inclined surface, are such that no part of the cutting element projects beyond the peripheral surface of the stud as viewed axially thereof. The cutting element may be so shaped and located that it initially projects beyond the peripheral surface of the stud, the projecting portions subsequently being removed, for example by grinding.

Abstract: A rotary drill bit for use in drilling or coring deep holes in subsurface formations comprises a bit body having a shank for connection to a drill string, a plurality of cutting elements 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. At least some of the cutting elements are each mounted on a stud which is received in a socket in the bit body, there being provided within the socket and disposed around at least a portion of the periphery of the stud resiliently compressible retaining means, such as a corrugated sleeve, which is formed separately from the stud and bit body and is resiliently compressed between the stud and the wall of the socket so as frictionally to retain the carrier in the socket.

Abstract: A method of forming a cutting structure for a rotary drill bit comprises brazing a thermally stable polycrystalline diamond cutting element to a carrier, the carrier being formed of a material such that, at the brazing temperature, the difference in coefficient of thermal expansion between said material and the polycrystalline diamond material is less than the difference in coefficient of thermal expansion between tungsten carbide and the polycrystalline diamond material. A suitable carrier material is silicon carbide.

Abstract: A rotary drill bit for use in drilling deep holes in subsurface formations comprises a bit body having a leading face and a gauge region, a plurality of cutting elements mounted at the surface of the leading face of the bit body, a passage in the bit body for supplying drilling fluid to a plurality of openings in the leading face of the bit body, and one or more junk slots in the gauge region of the bit body, whereby drilling fluid emerging from the openings flow over the leading face of the bit body and past the cutting elements thereon, so as to cool and clean the cutting elements before exiting through the junk slot.

Abstract: A method of manufacturing by a power metallurgy process a rotary drill bit including a bit body having an external surface on which are mounted a plurality of preform cutting elements, and an inner passage for supplying drilling fluid to at least one nozzle located in a socket at the external surface of the bit. The method includes the steps of forming a hollow mould for moulding the bit body, packing the mould with powdered material, such as tungsten carbide powder, and infiltrating the material with a metal alloy in a furnace to form a matrix. Before packing the mould with the powdered material, there is positioned in the interior surface of the mould at least one former which projects into the interior of the mould space at the desired location for a nozzle socket, the former having an external screw thread whereby the matrix material packed around the former becomes shaped with a corresponding internal screw thread.

Abstract: A cutting element for a rotary drill bit comprises a thin hard facing layer, defining a front cutting face, bonded to a less hard backing layer. The backing layer is of non-uniform thickness, for example is wedge-shaped, and is thicker adjacent the cutting edge of the facing layer than it is over the rest of the area of the facing layer. The rear surface of the backing layer of the cutting element is bonded to a surface on a carrier which is mounted in the bit body. The backing layer of the cutting element may be formed in two portions: a front portion which is bonded to the hard facing layer and a second, wedge-shaped portion which is bonded subsequently to the rear surface of the first portion.

Abstract: A method of making a rotary drill bit comprises forming a hollow mould for moulding at least a portion of the bit body, packing at least a part of the mould with powdered matrix material, and infiltrating the material with a metal alloy in a furnace to form a matrix, the alloy being a copper based alloy containing phosphorus and being selected to provide an infiltration temperature which is not greater than 850.degree. C. and preferably not greater than 750.degree. C.

Abstract: A method of manufacturing by a powder metallurgy process a rotary drill bit including a bit body having a plurality of cutting elements mounted on the outer surface thereof comprises the steps of forming a hollow mould for moulding at least a portion of the bit body, packing the mould with powdered matrix material, and infiltrating the material with a metal alloy in a furnace to form a matrix. Before packing the mould with powdered matrix material, there are positioned in spaced locations on the interior surface of the mould a plurality of cutting elements, each of which is formed of a material, such as a polycrystalline diamond material, which is thermally stable at the temperature necessary to form the matrix. Also positioned in the mould, adjacent the rearward side of each cutting element, is a support material such that, at least after formation of the matrix, the support material has a higher modulus of elasticity than the matrix.

Abstract: A rotary drill bit, for use in subsurface formations, comprises a bit body, a passageway for drilling fluid within the body, communicating with nozzles in the external surface of the body, preform cutting elements mounted on the body for cutting or abrading the formation, and a number of elongate fences upstanding from the external surface of the body to control the flow of fluid from the nozzles and past cutting elements. Each fence is resiliently deformable, for example being in the form of a brush having metal bristles, so that, in use, the free elongate edge of the fence is urged resiliently into contact with the surface of the formation being cut or abraded by the cutting elements. Since each fence is resiliently deformable it will at all times firmly engage the formation to provide an effective seal, regardless of variations in depth of cut of the cutting elements.

Abstract: A rotary bit for use in subsurface formations comprises a bit body having a central bore (4), the body having a leading face (1) and a trailing gauge region (2), walls (7) on the bit dividing the face into fluid channels, cutting elements C being present on at least some of the walls, and passageways (5) connecting the bore (4) to openings (6) in the fluid channels. At least two wall portions (7) are arranged relative to each openings (6) so that the fluid emerging from the opening is directed to travel first inwardly towards the central axis of the bit before travelling outwardly to the gauge region (2).