GEARING

the general term used for the means of transmitting rotary motion, covering such power and motion transmitting devices as the belt, rope, chain and friction drives as well as toothed wheels. General usage, however, has limited the term to toothed and worm wheels. These fall into the following cla es: Spur Wheels, wheels whose peripheries consist of a series of projections or teeth. The axes of the teeth are parallel to the wheel axis, the shape and size of the teeth are such as to permit their meshing with similar gears. Spur gears are used to transmit power between shafts which are parallel but not coincident. Bevel Gears have teeth cut on the surface of a cone, whose axis is the axis of the gear. The shape of the teeth are similar to those of spur gears. They are used to transmit power between shafts whose axes are not parallel but which intersect. Helical Gears resemble spur gears, but the axes of the teeth form part of a helix. Used in the same manner as spur gears, they are stronger and more rugged. Worm Gears consist of a worm meshing with a special toothed wheel, and are used to transmit power between shafts whose axes are not parallel, and do not intersect.