Abstract: A drilling tool (10) includes a pilot bit (14) and a plurality of mills (16) encircling the pilot bit. The pilot bit and the plurality of mills are each driven by a separate, hydraulically powered turbine or positive displacement motor. (20) The drilling tool does not include a transmission for transmitting power from the turbine or motor to any of the plurality of mills or the pilot bit.

Abstract: An earth boring tool includes two coaxially-aligned, positive displacement motors. One motor turns a pilot bit and the other turns a reamer concentric with the pilot bit. The central bit bores the center of the hole and the reamer enlarges it. The central bit is rotated relatively faster, while rotation of the larger diameter reamer is relatively slow. The tool can thus be used to bore larger diameter holes without slowing drilling rates or adversely affecting performance of the cutter elements due to higher tangential velocities.

Abstract: A drilling tool (10) includes a pilot bit (14) and a plurality of mills (16) encircling the pilot bit. The pilot bit and the plurality of mills are each driven by a separate, hydraulically powered turbine or positive displacement motor. (20) The drilling tool does not include a transmission for transmitting power from the turbine or motor to any of the plurality of mills or the pilot bit.

Abstract: The present disclosure is summarized as an improved cutting tooth for mounting on a stump cutting wheel driven by a suitable power plant. The tooth itself includes a long root to enable it to be clamped on the cutting wheel. When appropriately clamped, it is held with an extending neck terminating in a planar face. The face is constructed with an improved PDC hard surface layer. This is attached by a suitable WC-Co sintered alloy which joins the PDC layer to the tooth. This enables more certain anchoring of the PDC layer to the tooth. This enables more certain anchoring of the PDC face so that it does not break or flake during use and operation.

Abstract: An insert construction is set forth comprising a right cylinder insert body crowned with a PDC crown bonded thereto defining an interface between the two materials. The interface construction is described in geometric terms. The interface includes irregular curvilinear sided depressions to enhance the interface grip between the two materials thereby reducing shear stress concentration which might damage the PDC crown. Other failure modes are reduced also. Relationships are set forth in the amount, depth, and shape of the depressions.