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### Classification of Gears

Classification of Gears Points : classification of gears Gears or toothed wheels can be classified as follows:
1. According to position of axes of shafts. The axes of two shafts among which motion is to be transmit, can be
(a) Parallel
(b) Intersecting
(c) Non-intersecting and non-parallel.

Two parallel and co-planar shafts attached through the gears. These gears are call spur gears and agreement is identified as spur gearing. These gears contain teeth equivalent to axis of wheel. An additional name given to spur gearing is helical gearing, in which teeth are inclined to axis. Single and double helical gears between parallel shafts are shown. The purpose of double helical gear is to balance out end thrusts that are induce in single helical gears as transmit load. Double helical gears are identified as herringbone gears. A pair of spur gears is kinematically equal to a pair of cylindrical discs, keyed to a parallel shaft have line contact.

Two non-parallel or intersect, but coplaner shafts linked with gears. These gears are call bevel gears and arrangement is identified as bevel gearing. Bevel gears, like spur gears can also have their teeth inclined to face of bevel, in which case they are identified as helical bevel gears.

Two non-intersecting and non-parallel that is non-coplanar shafts attached with gears. These gears are called skew bevel gears or spiral gears and arrangement is identified as skew bevel gearing or spiral gearing. This type of gearing also has a line contact, rotation of which about axes generates two pitch surfaces identified as hyperboloids.

Notes:
(i) As equivalent bevel gears (having equal teeth) attach two shafts whose axes are equally perpendicular, then bevel gears are known as mitres.
(ii) A hyperboloid is solid formed through revolving a straight line on an axis (not in same plane), such that each point on line remains at a constant distance as of the axis. (iii) Worm gearing is effectively a form of spiral gearing in which shafts are generally at right angles.
According to peripheral velocity of gears. Gears, according to peripheral velocity of gears, can be classified as:
(a) Low velocity
(b) Medium velocity
(c) High velocity
Gears have velocity below 3 m/s are term as low velocity gears and gears have velocity among 3 and 15 m / s are identified as medium velocity gears. If velocity of gears is above 15 m / s, then these are call high speed gears.
According to type of gearing. Gears, according to type of gearing, can be classify as:
(a) External gearing
(b) Internal gearing
(c) Rack and pinion.

In external gearing the gears of two shafts mesh externally by each other. (a). The larger of these two wheels is called spur wheel or gear and the smaller wheel is called pinion. In an external gearing, the motion of the two wheels is always unlike (a). In internal gearing, gears of two shafts mesh inside by each other. (b). The larger of these two wheels is call annular wheel and smaller wheel is call pinion. In an inside gearing, motion of wheels is always like. (b). At times, gear of a shaft meshes externally and internally by the gears in a straight line.

Such a type of gear is call rack and pinion. Straight line gear is call rack and circular wheel is call pinion. A small consideration will show that by help of a rack and pinion, we can change linear motion into turning motion and vice-versa.
According to position of teeth on gear surface. Teeth on gear surface can be
(a) Straight
(b) Inclined
(c) Curved.

Spur gears have straight teeth while helical gears contain their teeth inclined to wheel rim. In case of spiral gears, teeth are curved over rim surface.