Method of drill bit manufacture

A method of producing a drill bit body with a plurality of recesses and passages for receiving drill bit components and the external surface thereof coated with an integrally formed layer of a refractory hard metal, which comprises

• providing a refractory mold having an internal configuration corresponding closely to the external configuration of a finished bit body and having a plurality of relatively soft metal plugs protruding from the walls thereof in locations corresponding to the recesses in the bit body in which said drill bit components are to be positioned,
• supporting a coating of sintered refractory metal particles on the inner surface of said mold,
• melting a metal and heating the same above the melting point of the matrix metal of said refractory metal particles,
• casting said molten metal into said mold in contact with said refractory metal particles to effect at least a partial desintering of said particles and produce a casting having a composite structure with the surface being coated with said particles for a substantial depth and with said soft metal plugs extending through said coating,
• removing said casting from said mold, and
• drilling out said metal plugs from said casting to produce recesses in said body sized to receive said drill bit components.

A method of producing a shaped metal body with a plurality of recesses and passages and the external surface thereof coated with an integrally formed layer of a refractory hard metal not extending into said recesses and passages, which comprises

• providing a refractory mold having a selected internal configuration and having a plurality of relatively soft metal plugs protruding from the walls thereof in locations corresponding to the recesses and passages in said shaped body,
• supporting a coating of sintered refractory metal particles on the inner surface of said mold,
• melting a metal and heating the same above the melting point of the matrix metal of said refractory metal particles,
• casting said molten metal into said mold in contact with said refractory metal particles to effect at least a partial desintering of said particles and produce a casting having a composite structure with the surface being coated with said particles for a substantial depth and with said soft metal plugs extending through said coating,
• removing said casting from said mold, and
• drilling out said metal plugs from said casting to produce recesses and passages in said body of selected sizes and locations.