Drill heads come in many sizes shapes, and styles. The most common drill heads are theduckbill bit for cutting and steering. This style of head has a cavity in the center to house the electronic locating equipment.

Passages for drilling fluid are routed around the centercavity to cool the locating electronics in the head. The duckbill or cutting bit attaches to the front of the drill head at a tapered angle. It is this angle that causes the drill head to change direction of travel when thrusting forward with no rotation.

Moving any direction is possible with stop rotating the drill string and pushing forward on the drill rods. The tapered angle of the duckbill forces the drill head to deflect from the original path in the direction where the duckbill is pointed. In order for this system to work, the driller must know the location of the drill head and its orientation.

 

The cutting tool on the drill head is selected specifically for the formation being drilled. Carbide tipped blades, conical bits, and toothed bits are used where necessary.

Mud motors are used to drill in rock or very hard formations. Mud motors are more complex than other styles of drill heads and require more support equipment. As the name implies, the drill head is actually a motor that rotates a cutting bit or tri-cone. The rotation of the motor is created by the flow of the drilling fluid (mud) being forced through it. Mud volumes of more than four hundred liters per minute are common depending on the size of the mud motor. Steering with a mud motor requires a "bent sub" between the mud motor and the drill stem.

A bent sub is a short piece of threaded drill stem that has a small bend in it. It is the orientation of the bend in the sub that determines the direction that the head travels. Several manufacturers have designed air hammers for horizontal directional drilling. These tools allow to direct the drill in very hard formations like granite.