Rotary drill bit

A rotary drill bit assembly comprising a drill bit body, at least one trunnion formed integrally with the drill bit body, a rotary cutter rotatably supported on the trunnion by at least two rows of balls, said trunnion being a one-piece member, means defining a raceway groove formed integrally in the trunnion for each of the ball bearings, means defining a raceway groove in the interior peripheral surface of said rotary cutter for each of the ball bearings, both said ball bearing assemblies securing the rotary cutter against axial withdrawal from the trunnion, means defining filling ports in the drill bit body for each of the rows of ball bearings, each filling port terminating at its inner end in the corresponding raceway for one of the rows of balls, each filling port being separate and disposed in said trunnion at different angles, and a filler pin for closing each filling port having a terminal end which complements the cross section of the raceway groove, said arrangement providding a trunnion construction which resists bending fracture during mounting and dismounting of the rotary drill bit so it is able to withstand heavy axial impact loads.