Modern churn drill equipment is made up in two principal sizes, both of which are portable and embody the same mechanical design.  The smaller size is used for shallow drilling, commonly in placer deposits. Depths of 500 feet are attained without difficulty in a moderately soft rock similar to altered granite, and 600 or 700 feet can be reached under favorable conditions. This type of drill is also employed for drilling blast holes in quarry and pit mining. The larger size "swings" a weight of tools up to 6000 pounds and normally drills to depths of 1000 or 1200 feet. Under favorable conditions, in which the rock is evenly firm with a relative absence of faults, shear zones, joints, bedding plane partings, etc., depths of 2000 feet or more can be gained.

Drilling is accomplished by imparting a rectilinear motion, with a magnitude of 18 inches to 3 feet, and a speed of 30 to 60 strokes per minute, to the cable or rope on which the bit is suspended. On earlier rigs the drilling cable was attached to one end of a center-pivoted walking beam actuated by a crank and rod. Power was supplied by a steam engine. Present models employ internal combustion or electric power, and the stroke is imparted to the drilling cable directly by a lateral pull from a crank, rod, and pulley assembly. This type of machine is more compact and portable. The choice of power, internal combustion or electric, is dependent on local conditions. It is the opinion of some drillers that the internal combustion engine, due to power lag, imparts a better "snap" to the cable than does the electric motor.

A wide assortment of accessory equipment is usually required. As drilling progresses, the hole is successively reduced in diameter, requiring a set of bits and casing for each size of hole. Too, a great variety of "fishing" tools must be employed when the cable breaks and tools or bailer are dropped in the hole, or when the casing breaks or becomes unjointed. A complement of these special tools is needed for each hole size.
Under normal conditions a hole is begun with a bit from 8 to 12 inches in diameter. Successive 2-inch reductions in bit diameter are made as the hole is deepened and strings of casing are installed. Under particular conditions the hole may be started with a bit as large as 26 inches in diameter. Holes have been finished with bits as small in diameter as 2 1/2 inches; although the speed of drilling a hole with such small diameter tools is very low, the cost is high, and the sample is less reliable.
The larger size rig requires preparation of a level area about 3 O feet by 75 feet adjacent to the location to be drilled.

Drill rigs are usually mounted on self-propelled wheels or Caterpillar treads, but occasionally they must be pulled from one location to another by truck or tractor. In any case, a road is graded to the drill site.

The size and power of the drill rig governs the road gradient, sharpness of turns, etc. However, some of the newer models can negotiate very steep and tortuous roads.