Abstract: A drill bit suited for impact-assisted directional boring in rock includes a bit body having a frontwardly facing, circular main cutting surface having a number of main cutting teeth disposed thereon. A gage cutter extends radially outwardly from the main cutting surface, which gage cutter mounts at least one frontwardly facing gage cutting tooth thereon suitable for cutting in a circle during straight boring and over an angle defined by less than a full rotation of the bit in order to steer the bit. A heel on an outer side surface of the bit body at a position opposite to and behind the gage tooth provides a reaction surface for the gage cutter. The bit body and gage cutter have a nearly circular side profile along a front portion thereof such that a maximum radial clearance between the side profile and a side wall of a hole being drilled is not greater than about 10 percent of the radius of a circle cut by the gage tooth.

Abstract: A drill head of directional boring includes a bit, a holder for a device for detecting angular orientation of the bit, and a hammer including a striker, wherein the bit assembly, holder and hammer are connected head to tail with the bit at a front end. The bit has a frontwardly facing main cutting surface having a plurality of main cutting teeth disposed thereon and a gage tower extending radially outwardly from the main cutting surface, which gage tower has at least one frontwardly facing gage cutting tooth thereon suitable for cutting over an angle defined by less than a full rotation of the bit. In one embodiment, the main cutting surface is substantially flat and circular and has fluid ejection ports thereon, and the drill head has passages for conducting a drill fluid therethrough to the ejection ports.