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Wednesday, October 29, 2014

Ancient Drills (c. 35,000 B.C.E)

Early humans learn how to bore small holes.

It is thought that early man used a primitive drill - perhaps a modified spear - to pierce wood and animal skins. Much later, the woodworker of ancient Egypt refined this technique by making any necessary holes with a bow drill. Adapted from the fire-stick, it had a cord wrapped round it and was held taut with a bow. Holding the drill vertically, the operator moved the bow backward and forward, pressing downward on alternate turns, with an idle return stroke (There is also evidence of dental drilling from as long ago as 9000 B.C.E., accomplished by the same means.)
The Romans replaced the bow drill with the auger, but the bit frozen between turns. It was not until the Middle Ages that use of the carpenter's brace made continuous rotation fo the drill possible.

The term "drill" may either refer to the machine supplying the rotational energy needed for penetration, or to the "drill bit", which is the part that rotates and actually cuts into the material. Various kinds of drills have evolved to meet specific needs.

Any drill has the capicity to make small holes in wood or brick, but more powerful machines are required to create pipe-sized holes in masonry or metal. Modern drills include a chuck to grip the drill bits or simple attachements. Some drills have chucks that can be unscrewed in order to recieve larger attachments, such as sanding tools, wire brushes, grinding stones, and circular saws.

The tip of a drill bit is conical in shape with cutting edges. The fluted part, or body, of a drill is now usually made of hardened, high-carbon steel. The angle formed by the tapering sides of the point determines how large a chip is taken off with each rotation, The bit also has helical flutes, which affects the drill's cutting and chip-removal properties.