Hammasratta

Hammasratta, commonly called hammasratas in Finnish, is a gear—a toothed wheel that transmits rotation and torque between shafts when its teeth engage with those of another gear. Gears are used to change speed, torque, and direction of motion within mechanical systems.

Gears come in several basic types, including spur gears with straight teeth, helical gears with angled teeth, bevel gears for intersecting shafts, and planetary gear sets. The term hammasratta can refer to any of these as a generic toothed wheel, though in everyday Finnish, hammasratas is the standard word.

Tooth profiles are most commonly involute shapes, which provide smooth torque transmission and constant velocity ratio. Gears are designed using the module or diametral pitch, and meshing reduces or increases speed and torque via gear ratios.

Materials used for gears include steel, cast iron, or nonferrous alloys, and gears are manufactured by hobbing, broaching, shaping, or milling; finishing operations include heat treatment to improve hardness and wear resistance.

Applications of gears span automotive transmissions, clocks, industrial machinery, bicycles, and robotics. Important design considerations include gear ratio, efficiency, backlash, alignment, lubrication, and noise, all of which influence performance and longevity in mechanical systems.