Two stage large diameter drill bit

Abstract

A large diameter drill bit is disclosed that is capable of drilling various size bores. In the preferred embodiment, the drill functions as a raise bit for enlarging a pilot hole into a larger diameter hole by disintegrating the earth formations surrounding the pilot hole. In the primary stage, the raise bit includes a primary body supporting a plurality of yokes positioned at various radial locations thereon. A frusto-conical cutter is rotatively mounted on each yoke for contacting and disintegrating the above-mentioned earth formations, with the outermost cutters forming the gage row. For the second stage, in which larger diameter holes are to be drilled, a plurality of ear assemblies are provided for attachment to the primary body at circumferential locations between the outermost primary cutters. Each ear assembly comprises a unitary support frame having a yoke and cutter mounted thereon. A vertically oriented roller stabilizer is also mounted on each support frame. The ear assembly cutters are positioned to extend radially outwardly beyond the outermost cutters located on the primary body to form a new and expanded gage row. Each ear assembly support frame includes a plurality of locating pads which are adapted to register with mating pads located on the primary body and bolts are provided to extend through the interfaced locating pads to secure the support frame to the primary body.