UNDERGROUND DRILLING APPARATUS

A drilling apparatus can include a sonde housing that is elongated along a central longitudinal axis. The sonde housing has 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 is adapted for connection to a drill string and the distal end of the sonde housing includes a distal end face. The sonde housing further defines first and second sonde-housing fluid-delivery passages. The first and second sonde-housing fluid-delivery passages extend fluidly separately from one another throughout substantially an entire length of the sonde housing. The drilling apparatus can also include a rotary cutting tool that mounts to the distal end of the sonde housing. The rotary cutting tool can further define distinct first and second cutting-tool fluid-delivery passages. The first sonde-housing fluid-delivery passage can be in fluid communication with the first cutting-tool fluid-delivery passage. The second sonde-housing fluid-delivery passage can be in fluid communication with the second cutting-tool fluid-delivery passage.