The document discusses different types of gear trains used to transmit motion between rotating shafts in machines. It describes simple gear trains which use a single gear on each shaft, compound gear trains which use multiple gears on a shaft, reverted gear trains where the first and last gears share a common axis of rotation, and epicyclic gear trains where gears move in an orbital path relative to a fixed axis. Epicyclic gear trains are useful for achieving high speed ratios within a compact space and are used in applications like lathes, differentials, hoists, and watches.

1. Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade Accredited, ISO 9001:2015 Certified
Subject :- Theory of Machines II
T.E. Mechanical (302043)
Unit 3
3.1 Introduction of Gear Trains
By
Prof. K. N. Wakchaure(Asst Professor)
Department of Mechanical Engineering
Sanjivani College of Engineering
(An Autonomous Institute)
Kopargaon, Maharashtra
Email: wakchaurekiranmech@Sanjivani.org.in Mobile:- +91-7588025393

2. Gear Train
• In machines, rotary motion is transmitted from one shaft to other.
• A set of gears are employed to transmit motion from main shaft of
machine to various revolving elements.
• A combination of gears employed to transmit motion from one shaft to
other(s) is called ‘Gear train’.
2Subject :- Theory of Machines II
32 4
Train Gear Train
1
321

3. Types of Gear Train
• Simple Gear Train
• Compound Gear Train
• Reverted Gear Train
• Epicyclic Gear Train
3Subject :- Theory of Machines II
https://youtu.be/JOLtS4VUcvQ

5. Simple Gear Train
• When there is only one gear on each shaft, as shown in Fig, it is
known as simple gear train.
5Subject :- Theory of Machines II
Gear Train
321

6. Simple Gear Train
• When there is only one gear on each shaft, as shown in Fig, it is
known as simple gear train.
6Subject :- Theory of Machines II
Gear Train
321
These intermediate gears are
called idler gears, as they do not
effect the speed ratio or train
value of the system. The
idle gears are used for:
1. To connect gears where a large
centre distance is required, and
2. To obtain the desired direction
of motion of the driven gear (i.e.
clockwise or anticlockwise).
1
3
3
1
2
3
1
2
3
2
2
1
2
3
3
2
1
2
2
1
**
T
T
N
N
T
T
T
T
N
N
N
N
T
T
N
N
T
T
N
N





7. 3
21
4
Gear A
Gear C Gear D
Gear B
COMPOUND GEAR TRAIN
When there are more than one gear on a shaft, , it is called a compound train of gear.

8. 3
21
4
Gear A
Gear C Gear D
Gear B
COMPOUND GEAR TRAIN
When there are more than one gear on a shaft, , it is called a compound train of gear.
• Gear B and C are mounde on same shaft.
• Gear B and Gear C are having same speed (Maginitude).
• Gear B and Gear C are having same direction of Rotation.
32 NN 
2
1
2
1
T
T
N
N

4
3
3
4
T
T
N
N

4
3
2
1
3
4
1
2
**
T
T
T
T
N
N
N
N

4
3
2
1
1
4
*
T
T
T
T
N
N

• Gear B and C are mounde on same shaft.

9. 3
21
4
Gear A
Gear C Gear D
Gear B
COMPOUND GEAR TRAIN
• The advantage of a compound train over a simple gear train is
that a much larger speed reduction from the first shaft to the
last shaft can be obtained with small gears.
• If a simple gear train is used to give a large speed reduction,
the last gear has to be very large.
• Usually for a speed reduction in excess of 7 to 1, a simple train
is not used and a compound train or worm gearing is
employed.

10. REVERTED GEAR TRAIN
When the axes of the first gear (i.e. first driver) and the last gear (i.e. last
driven or follower) are co-axial, then the gear train is known as reverted
gear train
3
21
4
Gear A
Gear CGear D
Gear B
32 NN 
2
1
2
1
T
T
N
N

4
3
3
4
T
T
N
N

4
3
2
1
3
4
1
2
**
T
T
T
T
N
N
N
N

4
3
2
1
1
4
*
T
T
T
T
N
N

• Gear B and C are mounde on same shaft.

11. The velocity ratio and train value of gear train:
11Subject :- Theory of Machines II
Velocity ratio or speed ratio
The speed ratio of the gear train is defined as the ratio between speed of the driver to speed
of the driven.
(or) the ratio between number of teeth on driven gear to number of teeth on driver.
Velocity or speed ratio =
speed of driver
speed of driven shaft
Speed Ratio=
number of teeth on driven gear
number of teeth on driver
Train value:
The train value is reciprocal Of the speed ratio.
Train Value =
speed of driven shaft
speed of driver shaft

12. REVERTED GEAR TRAIN
4321
4321
4321
4
3
2
1
**2**2**2**2
_
4__
3__
2__
1__
TTTT
TmTmTmTm
T
d
mas
rrrr
GearofRadiusr
GearofRadiusr
GearofRadiusr
GearofRadiusr








3r4r
2r1r

13. EPICYCLIC GEAR TRAIN
in an epicyclic gear train, the axes of the shafts, over which the gears are mounted, may move
relative to a fixed axis.
Epicyclic = epi- Upon
Cyclic-rotation
• Applications
• The epicyclic gear trains are useful for
transmitting high velocity ratios with gears of
moderate size in a comparatively lesser space.
• The epicyclic gear trains are used in the back
gear of lathe, differential gears of the
automobiles, hoists, pulley blocks, wrist
watches

14. Sun Gear= Rotates about own axis
Arm= Rotates about the axis of sun
gear at one end and another end
consist of Planet gear/s
• Mounted on another shaft
Planet Gear= Rotates about the
own axis as we all over the
periphery of Sun Gear (Epicyclic
action)
EPICYCLIC GEAR TRAIN
Sun Gear
Planet Gear
Arm

16. •Thank You…