A brief description on types of gear trains used in various day to day machines to operate them. Just to give a brief idea to the audience about these gear trains. References:- 1. Theory of Machines by R.S.Khurmi and J.K.Gupta

1. GEAR TRAINS
Presented By :-
Aditya Bose
SG-13901
B.E. (Mechanical)
bose.aditya95@gmail.com

2. INTRODUCTION
• A gear train is a combination of gear Used to transmit motion from
one shaft to another. It becomes necessary when it is reqired to
obtain large speed reduction within a small space. The following are
the main types of gear trains.
a)Simple gear train
b)Compound gear train
c)Reverted gear train
d)Epicyclic gear train

3. INTRODUCTION (Contd.)
• In simple gear trains, each shaft supports one gear. In a compound
gear train, each shaft supports two gear wheels except the last. In a
reverted gear train, the driving and the driven gear are coaxial or
coincident. In all these three types, the axes of rotation of the wheels
are fixed in position and the gear rotate about their respective axes.
However, it is also possible that in a gear train, the axes of some of
the wheels are not fixed but rotate around the axes of other wheels
with which they mesh. Such trains are known as planetary or Epicyclic
gear trains. Epicycle gear trains are useful to transmit very high
velocity ratios with gear of smaller sizes in a lesser size.

4. SIMPLE GEAR TRAIN:-
• A series of gear, capable of receiving and transmitting motion from one gear to another is called a
simple gear train. In it, all the axes remain fixed relative to the frame and each gear is on a
separate shaft (fig. 11.1).
• In a simple gear train we can observe the following:
• Two external gears of a pair always move in opposite directions.
• All odd-numbered gears move in one direction and all even-numbered gears in the opposite
direction. For example, gears 1,3,5, etc, move in the counter-clockwise direction.
• Speed ratio, the ratio of the of driving to that of the driven shaft, is negative when the input and
the output gears rotate in the opposite direction and it is positive when the two rotate in the
same direction. The reverse of the speed ratio is known as the train value of the gear train.
• All the gears can be in a straight line or arranged in a zig-zag manner. A simple gear train can also
have bevel gears.
• Let T= number of teeth on a gear
• N= speed of a gear in rpm.

5. SIMPLE GEAR TRAIN (Contd.)
2
3
3
2
.
T
T
N
N
ratioSpeed ==
Simple gear train in which
each shaft carries only one
gear
2
4
4
2
3
4
2
3
4
3
3
2
.
.
T
T
N
N
ratiospeed
T
T
T
T
N
N
N
N
ratioSpeed
==
×=×=

6. Compound Gear Train
• When a series of gears are connected in such a way that two or more
gears rotate about an axis with the same angular velocity, it is known
as compound gear train. In this type, some of the intermediate shafts,
i.e., other than input and the output shafts, carry more than one gear
shown in figure.

7. 4
5
3
4
2
3
5
2
44
33
4
5
3
4
2
3
5
4
4
3
3
2
′′
′
′
′′
′′
××===
=
=
××=××=
T
T
T
T
T
T
N
N
N
N
i
NN
NN
T
T
T
T
T
T
N
N
N
N
N
N
i
output
input
3
4
2
3
4
2
33
3
4
2
3
4
3
3
2
′
′
′
′
×===
=
×=×=
T
T
T
T
N
N
N
N
i
NN
T
T
T
T
N
N
N
N
i
output
input

8. 3
4
1
2
4
1
32
3
4
1
2
4
3
2
1
T
T
T
T
N
N
N
N
i
NN
T
T
T
T
N
N
N
N
i
output
input
×===
=
×=×=

9. Reverted Gear Train
• If the axis of the first and the last wheels of the compound gear
coincide, it is called a reverted gear train. Such an arrangement is
used in clocks and simple lathes where back gear is used to give a
slow speed to the chuck.

10. EPICYCLIC GEAR TRAIN
• A gear train having a relative motion of axes is called a planetary or an
epicyclic gear train. In an epicyclic gear train, the axis of atleast one of
the gears also moves relative to the frame.
• Consider two gear wheels S and P, the axes of which are connected
by an arm a. if the arm a is fixed, the wheels s and p constitute a
simple train. However, if the wheel S fixed so that the arm can roatate
about the axis of S, the wheel P would move around S. Therefore, it is
an epicyclic train.

12. The End