According to aim that a typical spur gear will used, design of spur gear changes. But in general, there are three types of spur gears are used.
The most general type of spur gear is the spur gears which has a solid hub. These spur gears are generally used in transmissions of machineries. Shaft is assembled inside the hole that is bored to this hub. Also keyways are machined on this hole for the assembly of keys. You can find a small screw hole on spur gears. These screw holes are machined because of the assembly of keys on spur gears. Solid hub spur gears can be thich compared with other types.
Also there is an another type of spur gear which are generally used in high diameters. Because of this high diameters, spoked design is used to save from material usage. There is a keyway is bored on this type spur gears and hub section can be smaller than solid hubbed spur gears.
Rack is an another and different type of spur gears which have straight geometry unlike other spur gears. Because of this straightness, they do not have the same teeth type with other spur gears.
From gear mechanisms, we do not want vibrations and noises. So, a proper design of teeth are important. For round spur gears, involute design of teeth are most appropriate to elmininate such problems like;
If you take a look at the involute design of mutual teeth that contacting to each other during rotation, there is a rolling between two contacting teeth. When a straight and perpendicular line is drawn from the contact region of involute teeth, this drawn line must be tangent to each base circles of spur gears.
It is invented that this involute design of spur gear teeth compensate nearly all the problems stated above.
This is a very basic demonstration of spur gear types and spur gear teeth design in terms of engineering.
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