Types of Toothed Gears:
The slipping of a belt or rope is a common phenomenon in the transmission of motion or power between two shafts. The effect of slipping is to reduce the velocity ratio of the system. In precision machines, in which a definite velocity ratio is of importance, the only positive drive is by means of toothed gears. The toothed gears may be classified as follows:
1. According to the position of axes of the shafts: The axes of the two shafts between which the motion is to be transmitted may be –
i. Parallel: When equal bevel gears connect two shafts whose axes are mutually perpendicular, then the bevel gears are known as mitres.
ii. Intersecting: A hyperboloid is the solid formed by revolving a straight line about an axis, such that every point on the line remains at a constant distance from the axis.
iii. Non-intersecting and Non-parallel: The worm gearing is essentially a form of spiral gearing in which the shafts are usually at right angles.
2. According to the peripheral velocity of the gears: The gears, according to the peripheral velocity of the gears may be classified as:
i. Low Velocity: The gears having velocity less than 3m/s are termed as low velocity.
ii. Medium Velocity: The gears having velocity between 3 and 15 m/s are known as medium velocity gears.
iii. High Velocity: If the velocity of gears is more than 15m/s, then these are called high velocity gears.
3. According to the type of the gearing: The gears, according to the type of gearing may be classified as:
i. External Gearing: In external gearing, the gears of the two shafts mesh externally with each other. The larger of these two wheels is called spur wheel and the smaller wheel is called pinion. In external gearing, the motion of the two wheels is always unlike as shown in fig:
ii. Internal Gearing: In internal gearing, the gears of the two shafts mesh internally with each other. The larger of these two wheel is called annular wheel and the smaller wheel is called pinion. In an internal gearing, the motion of thw two wheels is always like as shown in fig:
iii. Rack and Pinion: Sometimes, the gear of a shaft meshes externally and internally with the gears in a straight line. Such type of gear is called rack and pinion. The straight line gear is called rack and the circular wheel is called pinion. A little consideration will show that with the help of a rack and pinion, we can convert linear motion into rotary motion and vice-versa as shown in fig:
4. According to the position of teeth on the gear surface: The teeth on the gear surface may be –
i. Straight, ii. Inclined, iii. Curved