Gears

Gears are rotating machine elements with teeth that mesh with another gear to transmit torque and angular motion. They are used to change speed, torque, and the direction of a power source. A gear train consists of two or more gears in mesh; the ratio of output to input speed is the inverse of the gear tooth count ratio or diameter ratio.

Types include spur gears, which have straight teeth and are used for simple, high-load transmissions; helical gears, with angled teeth that run more smoothly and quietly but generate axial thrust; bevel gears, which transmit motion between intersecting shafts; and worm gears, where a screw-like worm meshes with a gear to achieve large reductions in a compact package. Internal gears have teeth on the inside of a ring and mesh with external gears.

Geometry and sizing: The pitch circle is the effective mesh surface. Gear ratio equals the number of teeth on the driven gear divided by the number of teeth on the driver gear. Sizing uses modules (metric) or diametral pitch (imperial). Tooth geometry is defined by pitch, addendum, dedendum, and clearance, with a typical pressure angle around 20 degrees.

Manufacture and materials: Common materials include steel, cast iron, bronze, and plastics. Manufacturing methods include hobbing, milling, shaping, and grinding, often followed by heat treatment and surface finishing. Proper lubrication and alignment reduce wear and improve efficiency. Gear systems can achieve high efficiency, though efficiency varies by type and load, with worm gears generally lower due to sliding contact.

Applications: Gears are fundamental in clocks, automotive transmissions, industrial machinery, robotics, conveyors, and many consumer and industrial devices requiring controlled torque and speed.