types of gears

In my previous post i have given details about the introduction to gears, now let us see the different types of gears. Many different forms of gears are used and the types most commonly used are,

• Spur gear - Gears whose axes are parallel and whose teeth are parallel to the centerline of the gear are called spur gears. They are used to transmit power from one shaft or element to another in case where those shafts have their axes parallel.
  

• Helical gear - Gears in which the teeth are cut in the form of helix around the gear. Helical gearing is used to connect parallel shafts as well as non-parallel, non-intersecting shafts. The pitch surfaces are cylindrical as in spur gearing, but the teeth, instead of being parallel to the axes, wind around the cylinders helical like screw threads.

• Spiral gear - Skew or spiral gearing is used to connect non-parallel, non-intersecting shafts. The pitch surfaces are cylindrical and the teeth have point contact. suitable for transmitting only small power.

• Bevel gear - When two shafts, the axes of which intersect, are to be connected by gearing, the wheels are known as bevel gears. The teeth are cut on a conical surface, such as would be represented by a truncated cone. Majority of bevel gear drives the shafts are at right angles, but in some cases the angles between the shafts may be either greater or less than 90 degrees, these are called as angular bevel gears.

• Worm and worm wheel - Worm gearing is essentially a special form of helical gearing in which the teeth have line contact and the axes of the driving and driven shafts are usually at right angles and do not intersect. The distinction between helical gearing may be explained as follows : if the number of threads or teeth is such that no one thread makes a complete turn, the gear is called a helical gear. Of on the other hand, a thread makes a complete turn, the result is a worm and the mating material is called worm wheel.

• Rack and pinion - The function is to transform circular motion to rectilinear motion : small gears are called pinions and racks are a series of teeth on a straight line. They may be considered as spur gears with infinite radii.