A down-the-hole drill produces large-bore holes with percussive action to break up hard rock and other materials. The name references the fact that early versions of this device were lowered into holes, followed by the rest of the drilling rig. For underground applications, a down-the-hole drill may actually be used in reverse, pushing up towards the surface of the Earth. Numerous manufacturers produce this equipment and accessory components like specialized drill heads and maintenance kits.
The design of a down-the-hole drill includes a drill head with a broad surface that may be textured with spikes or knobs. Drilling rigs feed compressed air or fluid to create rapid percussion that breaks up materials in the way of the drilling head. In addition, the pressurized materials flush the area around the down-the-hole drill to keep it clear so it can keep drilling without getting clogged by chips of rock, drilling fluid, and other materials. Whether the device is moved up or down, it can be advanced into the ground to make a large diameter hole.
When a down-the-hole drill is no longer needed, the drill string containing the drill head and instruments can be raised from the hole. Technicians can switch out components with the equipment they need for the next stage of production. This creates a high degree of flexibility on the job site for drill operators and their support crews. Rigs can also be periodically raised for inspection and maintenance tasks.
One common site where down-the-hole drills can be seen is at quarries. Technicians may use them to drill away sections of rock to create access points and collect valuable stone; this is more efficient than other drill types like rotary drills, which can require more energy to make comparably large holes. Blasting and other options are also available for quickly cutting through surface materials to gain access to useful minerals.
Companies routinely involved in drilling for exploration and production may have their own drilling rigs and equipment like down-the-hole drills. They are also available for rental in situations where one is needed temporarily. Rental equipment may be supplied with a technician to operate the drill, because there are safety concerns that may arise, making it easier for liability reasons to send a trained and authorized crew member to manage the equipment. This reduces the risk of injuries or problems that might be caused by an untrained person using equipment improperly.