Abstract: Method and apparatus for forming a base defining a trunnion and a portion of a leg for a roller-cone-type rock bit. A workpiece is rough formed to comprise leg work, having a preliminary end surface, and trunnion work extending angularly from the leg work. An interface plate is mounted on a holder of a lathe with an indexing surface thereof facing generally radially inwardly but angled to correspond to a desired angular orientation of a trunnion in a finished bit. The workpiece is removably mounted on the interface plate, with the preliminary end surface abutting the indexing surface, by at least one pin-type connector projecting from one of the surfaces into the other. The trunnion work is then turned on the lathe. Other parts of the machining of the workpiece may be performed by removing the workpiece from the first interface plate and similarly mounting it on plates adapted for other machines, but otherwise similar to the first plate.

Abstract: The method of making a roller cone rock bit wherein a main body having a tool joint adjacent one end and a plurality of leg stubs adjacent the other end, has the outer surfaces of those leg stubs on a common conical locus tapering longitudinally inwardly from the radially outer extremity to the radially inner extremity. A like number of cone bases have their trunnions emplaced in respective recesses in a common fixture, in which the recesses are oriented with respect to one another in the same manner as is desired for the relative orientation of the trunnions on the finished rock bit. The end surfaces of the leg extensions which are integral with these trunnions are then simultaneously machined to lie on a common conical locus corresponding to that of the outer surfaces of the leg stubs. The trunnions are removed from the fixture, and each of the adjoining leg extensions has its machined end surface mated with an welded to a respective one of the outer surfaces of the leg stubs.