Explain with neat sketch compound type Gear Train. Derive the equation for velocity ratio of gear train. Write it's application.
Compound Gear Train:
When there are more than one gear on a shaft, as shown in Fig. , it is called a compound
train of gear. In a simple train of gears do not affect the speed ratio of the system. But these gears
are useful in bridging over the space between the driver and the driven.
Gear trains inside a mechanical watch
But whenever the distance between the driver and the driven or follower has to be bridged
over by intermediate gears and at the same time a great ( or much less ) speed ratio is required,
then the advantage of intermediate gears is intensified by providing compound gears on
intermediate shafts. In this case, each intermediate shaft has two gears rigidly fixed to it so that
they may have the same speed. One of these two gears meshes with the driver and the other with
the driven or follower attached to the next shaft as shown in
In a compound train of gears, as shown in Fig., the gear 1 is the driving gear mounted on shaft A, 2M
gears 2 and 3 are compound gears which are mounted on shaft B. The gears 4 and 5 are also
compound gears which are mounted on shaft C and the gear 6 is the driven gear mounted on shaft
Let N1 = Speed of driving gear 1,
T1 = Number of teeth on driving gear 1,
N2 ,N3 ..., N6 = Speed of respective gears in r.p.m., and
T2 ,T3..., T6 = Number of teeth on respective gears.
Since gear 1 is in mesh with gear 2, therefore its speed ratio is
Applications – 1. Automobile gear box
3. Clocks/ watches
2. Lathe machines
4. Electro mechanical meter