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The outside diameter of a gear is the diameter of the addendum (tip) circle. In a bevel gear it is the diameter of the crown circle. In a throated worm gear it is the maximum diameter of the blank. The term applies to external gears, this is can also be known from major diameter. [1]
In the United States, the diametral pitch P is the number of teeth on a gear divided by the pitch diameter; for SI countries, the module m is the reciprocal of this value. [3]: 529 For any gear, the relationship between the number of teeth, diametral pitch or module, and pitch diameter is given by: = =
That combination of gears and wheel is said to be "26 gear inches." If the front chainring has 48 teeth and the rear sprocket has 24 teeth, then each turn of the pedals produces two turns of the rear wheel. This is equivalent to doubling the size of the drive wheel; that is, it is like a directly driven bicycle with a 52-inch wheel.
Module is a direct dimension ("millimeters per tooth"), unlike diametral pitch, which is an inverse dimension ("teeth per inch"). Thus, if the pitch diameter of a gear is 40 mm and the number of teeth 20, the module is 2, which means that there are 2 mm of pitch diameter for each tooth. [56]
The involute gear profile, sometimes credited to Leonhard Euler, [1] was a fundamental advance in machine design, since unlike with other gear systems, the tooth profile of an involute gear depends only on the number of teeth on the gear, pressure angle, and pitch. That is, a gear's profile does not depend on the gear it mates with.
When two toothed gears mesh, an imaginary circle, the pitch circle, can be drawn around the centre of either gear through the point where their teeth make contact. The curves of the teeth outside the pitch circle are known as the addenda, and the curves of the tooth spaces inside the pitch circle are known as the dedenda. An addendum of one ...
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This is the simplest form of bevel gear. It resembles a spur gear, only conical rather than cylindrical. The gears in the floodgate picture are straight bevel gears. In straight bevel gear sets, when each tooth engages, it impacts the corresponding tooth and simply curving the gear teeth can solve the problem.