At Lee Bates and Sons, we use a combination of rotary drilling and cable tool drilling to complete our wells depending on the location and history of the drilling site.
Most home wells are drilled to 6 or 8 inches in diameter. While commercial, municipal or irrigation wells are often drilled at larger diameters.
In rotary drilling, a drill bit is attached to a length of connected drill pipe. The drill bit will be made of tough metals such as tungsten, and as the drill is rotated, the bit acts to grind up the rock. The broken pieces (cuttings) are flushed upward and out of the hole by circulating a drilling fluid (sometime called drilling mud) down through the drill pipe and back to the surface. This drilling fluid also serves to cool and lubricate the drill bit, and by stabilizing the wall of the hole, it can prevent possible cave-in of unstable sands or crumbly rock before the well casing or well screen is installed. As the drill intersects water bearing rock formations water will flow into the hole. Most drillers carefully monitor the depth of water "strikes" and keep a note of the formations in which they occur.
Another drilling technique uses a "pounder" machine, usually referred to as cable tool drilling. With this method, a heavy bit is attached to the end of a wire cable and is raised and dropped repeatedly, pounding its way downward. Periodically, cuttings are bailed out of the hole. This method is slower and in many places has been replaced by rotary drilling. However the cable tool method is responsible for millions of successful wells around the world.