Abstract: A mold usable to form a drill bit body and a method for forming such a mold are disclosed. A shell is provided, the shell having a cavity. Fusible material, such as foundry sand, is provided into the cavity, then fused to form a solid insert within the shell. The solid insert is then modified, such as by machining, to form a mold having features usable to form a drill bit body having desired characteristics. Materials for forming the drill bit body can then be provided into the mold, for heating and cooling. Then, the drill bit body and mold can be removed from the shell. The shell is thereby reusable, while the mold, being formed from inexpensive fusible materials, can be removed or destroyed, if necessary, to free the drill bit body.

Abstract: A rotary drill bit for use in drilling holes in subsurface formations comprises a bit body having a leading face and a gauge region, a number of blades formed on the leading face of the bit and extending outwardly away from the axis of the bit so as to define between the blades a number of fluid channels leading towards the gauge region, a number of cutting elements mounted side-by-side along each blade, and a number of nozzles in the bit body for supplying drilling fluid to the fluid channels for cleaning and cooling the cutting elements. In each of the fluid channels, adjacent the gauge region, is an opening into an enclosed passage which passes internally through the bit body to an outlet which, in use, communicates with the annulus between the drill string and the wall of the borehole being drilled. The gauge region of the drill bit comprises a substantially continuous bearing surface which extends around the whole of the gauge region.