Abstract: A drill bit comprises a main body part having a shank for connection to a drill string, an end face, an internal passage for supplying drilling fluid to the end face, a number of blades extending from the end face outwardly and longitudinally of the central axis of rotation of the bit, and a number of cutters mounted on each said blade. Each blade comprises a central metal core at least partly surrounded by solid infiltrated matrix material.

Abstract: A rotary drill bit for drilling holes in subsurface formations comprises a bit body having a leading face and a gauge region, and a plurality of blades formed on the leading face of the bit body and extending outwardly away from the axis of the bit towards the gauge region so as to define a fluid flow channel between the leading edge of each blade and the trailing edge of the adjacent preceding blade. A plurality of cutting elements are mounted along the leading edge of each blade, and there is provided, in one or more of the channels, a main nozzle which directs fluid along the leading edge of one blade so as to clean and cool the cutting elements on it, and a subsidiary nozzle which is located and orientated so as to direct fluid along the trailing edge of the preceding blade in a direction opposite to the direction of flow from the main nozzle, so as to tend to enhance partial recirculation of fluid flow in the flow channel between the blades.