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The electrically powered motor of a power drill, cooled by a fan, turns a shaft at high speed. The shaft connects,in turn, to a system of gears that rotates a chuck even faster. Clamped by the chuck, a sharp bit cuts out the hole, and at the same time the bit's screw-shaped grooves channel the waste out of the hole. For drilling hard materials, many power drills have a hammer mechanism: when this is operated a ratchet in the gearcase causes the chuck and bit to pound in and out as they drill. A hand drill, although slower and less forceful than a power drill, is easier to control. For cutting wide holes, carpenters often prefer a brace-and-bit. This acts like a lever: the bowed handle than the bit, turning the bit with extra force.
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