The circular pitch line, as opposed to the diametral pitch, is the same as the pitch circle. It is a line which bisects all the teeth of a toothed wheel.
The rolling circle is the same as the circular pitch line.
Diametral means pertaining to a diameter or the length of a diameter; hence a diametral pitch is a system of measures or enumeration based upon the diameter instead of the circular pitch line; it is used very generally in spacing for fine tooth gear. Wheels of this description usually have their teeth cut in a gear-cutting machine, i. e., medium and fine tooth gears.
Fig. 265.
A cog wheel is the general name for any wheel which has a number of cogs placed around its circumference.
When the teeth of a wheel are made of the same material and formed of the same piece as the body of the wheel, they are called teeth; when they are made of wood or some other material and fixed to the circumference of the wheel, they are called cogs; see [fig. 265].
A pinion is a small wheel. When two toothed wheels act upon one another, the smaller is generally called the pinion. The terms trundle and lantern are applied to small wheels having cylindrical bars instead of teeth. The teeth in pinions are sometimes termed leaves; in a trundle, staves. See [fig. 273].
The wheel which acts is called a leader or driver; and the wheel which is acted upon by the former is called a follower or the driven. When a screw or worm revolves in the teeth of a wheel, the latter is termed a worm wheel or worm gear; see [fig. 270]. When a pinion acts with a rack having teeth, we speak of rack and pinion. When the teeth are on the inside of the rim, and not on the periphery, the wheel is termed an internal gear; see [fig. 272].
Two wheels acting upon one another in the same plane are called spur gear; the teeth are parallel with the axis. When wheels act at an angle, they are called bevel gear.