Abstract: A self-advancing conical boring tool with a tapered frame for supporting roller cutters, each of which has a frusto-conical body with a plurality of teeth randomly disposed about its periphery. Each roller cutter is constrained within a pair of thrust bearings and a pair of self-aligning spherical roller bearings for free rotation about an axis that is both oblique and skewed relative to a longitudinal axis of the tool. A flexible diaphragm is captively held to the frame proximate each roller cutter and forms a pressure compensated chamber for a bearing lubricant, one face of the diaphragm being adjacent a thrust bearing and the other face of the diaphragm being exposed to the environment through a vent.

Abstract: A self-advancing conical boring tool with frusto-conical roller cutters rotatably mounted to a tapered frame by means of self-aligning spherical roller bearings. Each roller cutter is constrained within a pair of spherical roller bearings for free rotation about an axis that is both oblique and skewed relative to a longitudinal axis of the frame.