drill

drill, tool

drill, tool used to create a hole, usually in some hard substance, by its rotary or hammering action. Many different tools make up the drill family. The awl is a pointed instrument used for piercing small holes. In its early form it was a thorn or a tool of bone or chipped flint; many prehistoric awls of flint have been found. The gimlet, which consists of a cross handle holding a metal shaft with a screw point, is used for boring small holes. Its principle and that of a similar tool, the auger, were known and used in ancient times, but the tools were much improved in the Middle Ages. The auger has a cross handle containing a shaft that usually ends with a central screw-shaped point; the point acts to pull two knife edges about it into the material to do the actual cutting. Spiral channels extend part way up the shaft to allow chips to be removed from the hole. The term auger is also applied to various augerlike tools. More elaborate types of drills are composed of two main parts: a replaceable device that does the actual cutting, called a bit, and a second device that drives it. Both devices may be referred to as drills. Two common types of rotary bits are the auger and the twist bit. Hand-powered rotary driving devices include the hand drill, which has a crank that transmits turning power to the bit through a gear and pinion, and the bit brace, which is a bow-shaped device that is rotated to turn a bit. Motor-powered rotary driving devices include the drill press and the portable electric drill, both used at home or in industry for cutting holes in such materials as metal, wood, and plastic. The core drill cuts an annular hole through minerals. For a small hole the drill bit may contain diamonds, which bore a hole by their abrasive action when they are rotated. A rotary oil well drill uses a bit containing either rolling cutters with hard teeth or a fixed, chisel cutting edge. The percussive types of drill force a bit to move forward by a hammering action that chips away material, instead of cutting or abrading it. For example, an air percussion drill chips through rock with a cross-shaped bit driven by a piston; the similar churn drill is lifted and dropped by cable. One special kind of drill, the fusion drill, creates a hole by melting or flaking minerals with an oxyacetylene torch. An agricultural implement for planting certain seeds or for placing fertilizer in the soil is called a drill. Small drills for gardens are pushed by hand; large drills for field work are drawn by horses or tractors. The agricultural drill is named for its special uses, e.g., the grass drill and the grain drill, or for its construction, as the disk drill and the hoe drill. The fertilizer drill is commonly combined with the seed drill.

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drill, in zoology

drill, monkey: see mandrill.

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drill

Tool to make holes, usually by revolving. Drills, gimlets, and augers have cutting edges that detach material to leave a hole. Drilling usually requires high speed and low torque, with little material being removed during each revolution of the tool. The earliest (perhaps Bronze Age) drill points had sharp edges that ultimately developed into arrow shapes with two distinct cutting edges. This shape was effective and remained popular until the late 19th century, when factory-made, spiral-fluted twist drills became available at reasonable cost to displace the blacksmith-made articles. Rotating drill bits containing diamonds or other hard materials are used for drilling rock, as for tunnels or oil wells. See also drill press.

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drill

In military science, the preparation of soldiers for performance of their duties through the practice of prescribed movements. It trains soldiers in battle formations, familiarizes them with their weapons, and develops a sense of teamwork and discipline. Today close-order drill is used for marching, ceremonies, and parades; combat drill is used to practice the looser routines of battle. It was introduced by the Greeks, who practiced the maneuvers of the phalanx. Careful training of the legions was a major factor in the Roman Empire's dominance. After Rome's decline, drill largely disappeared and battles became free-for-all combats. Gustav II Adolf of Sweden led in reintroducing drill techniques in early 17th-century Europe.

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drill

Drill (Mandrillus leucophaeus).

(credit: J. Kohler/Bavaria-Verlag)

Large, short-tailed monkey (Mandrillus leucophaeus, family Cercopithecidae). Formerly found from Nigeria to Cameroon, it is now restricted to remote forest regions of Cameroon because of hunting and deforestation. Like the related mandrill, the drill is stout-bodied and has vividly coloured buttocks. The male is about 32 in. (82 cm) long and has a black face. Its lower lip is bright red, the hairs around the face and a tuft behind the ears are yellowish white, and the rest of the fur is olive-brown. An omnivore, it is mainly terrestrial, gregarious, and powerful, and it can fight ferociously if molested.