Abstract: Discloses a lubricant circulating system for a rotary drilling bit including a lubricating space defined between a rotary cone cutter and a journal shaft extending from the bit body, the body defining a lubricant supply passageway connecting the lubricating space with a substantially cylindrical inlet chamber of a lubricant reservoir and with the centerline of the supply passageway being disposed substantially tangential with the cylindrical wall of said inlet chamber to form a restrictive vortex flow passage from the supply passageway into said reservoir and a nonrestrictive return flow passage, the body defining a lubricant exhaust passageway connecting the lubricating space through a substantially cylindrical outlet chamber into a discharge passageway forming part of the reservoir and with the centerline of the discharge passageway being disposed substantially tangential with the cylindrical wall of the outlet chamber to form a restrictive vortex flow passage from the reservoir into the outlet chamber and