Underground drilling apparatus

A drilling apparatus comprising:

• a sonde housing that is elongated along a central longitudinal axis, the sonde housing having a length that extends along the central longitudinal axis from a proximal end of the sonde housing to a distal end of the sonde housing, the proximal end of the sonde housing being adapted for connection to a drill string and the distal end of the sonde housing including a distal end face, the sonde housing defining first and second pin openings that extend from the distal end face proximally into the sonde housing, the first and second pin openings of the sonde housing having central axes that extend along the central longitudinal axis of the sonde housing, the sonde housing also including a top platform positioned adjacent to the distal end of the sonde housing, the top platform facing in an upward direction, the sonde housing defining a first cross-slot at the top platform, the first cross-slot being transverse relative to the central longitudinal axis of the sonde housing and having an open top side, the sonde housing also including a tongue positioned on the top platform;
• a rotary cutting tool that mounts to the distal end of the sonde housing, the rotary cutting tool including a head portion having a distal side and a proximal side, the distal side including a distal face in which a plurality of cutting teeth pockets are defined, the proximal side including a proximal face that opposes the distal end face of the sonde housing, the rotary cutting tool defining first and second pin openings that extend distally from the proximal face and respectively co-axially align with the first and second pin openings of the sonde housing, the rotary cutting tool also including a proximal extension that extends proximally from the proximal face of the head portion, the proximal extension having a bottom side that opposes the top platform of the sonde housing, the proximal extension defining a groove that receives the tongue of the sonde housing in an insertion direction that extends along the central longitudinal axis of the sonde housing, the bottom side of the proximal extension also including a second cross-slot that is transverse relative to the central longitudinal axis of the sonde housing, the second cross-slot including an open bottom side and being positioned to oppose the first cross-slot of the sonde housing;
• first and second pins having first ends respectively received in the first and second pin openings of the sonde housing and second ends respectively received in the first and second pin openings of the rotary cutting tool;
• cutting teeth mounted within the cutting teeth pockets of the rotary cutting tool;
• and
• a cross pin mounted within the first and second cross-slots for limiting relative movement between the sonde housing and the rotary cutting tool along the central longitudinal axis of the sonde housing.