The following presentation includes information on gears, application of gears, gear trains, velocity ratio, and few simple solved examples based on the above stated topics

1. Babaria Institute of Technology
Prepared by
Burhani Burhan A : (011)
Bhimani Vipul S : (010)

2. Gears and Gear train

3. • Types Of Gears
(Bevel and Worm gear)
• Applications Of Gears
• Gear Trains
(simple and compound gear train)
• Velocity Ratio
• Examples

4. According to the position of axes of the shafts.
a. Parallel shaft
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
b. Intersecting shaft
Bevel Gear
c. Non-intersecting and Non-parallel shaft
worm and worm gears

6. • Kinematically, the motion between two
intersecting shafts is equivalent to the rolling of
two cones, assuming no slipping.
• These gears are known
as bevel gears.

7. • When power is required to be transmitted from
one shaft to another shaft which are interesting
to each other then bevel gears are used.
• Bevel gears are useful when the direction of a
shaft's rotation needs to be changed .
• The angle between two
shafts is 90 degrees.

8. • Standard bevel gears have teeth that are cut
straight. The teeth point toward the apex of the
cone on which they are machined.
• The teeth of these
gears are formed on
a conical surface.
Apex of the cone

9. • Application
locomotives,
marine applications,
automobiles,
printing presses,
cooling towers,
power plants,
steel plants,
railway track inspection machines.

10. The bevel gears are of three types:-
1. straight bevel gears
2. spiral bevel gears
3. zerol (hypoid) bevel gears

11. • In straight bevel gears the teeth are formed
straight on the cone.
• They are parallel to the axis of the gear.
• They are used for transmitting power between
intersecting shafts.
• They can operate under high speeds and high
load.
• They are suitable for higher velocity ratio.
• Application-automotive differential gear box,
right angle drives of blenders

12. •Standard bevel gears are mainly used in low speed
(less than 500 rpm) applications. At high speeds they
become noisy. They are typically used in applications
such as hand drills.

13. • In spiral bevel gear the teeth are formed at an angle
with respect to its axis .
• The contact between two meshing teeth is gradual
and smooth from start to end ,as in case of helical
gears.
• Because of spiral tooth, the contact length is more &
contact ratio is more. They operate smoother than
straight bevel gears and have higher load capacity.
• But ,their efficiency is lower then straight bevel
gears .

14. Spiral bevel gears are typically used for high speed
(greater than 500 rpm) and performance
applications, where low noise and vibration levels are
important. They are typically used in transmission
systems.

15. • These gears are also used for right angle drive in
which the axes do not intersect .
• These drives requires good lubrication to reduce
the friction and wear.
• Their efficiency is lower then other two types of
bevel gears.
• Application :- in current day automobile drive line
power transmission system.

17. • Worm and worm gears are used to transmit power
from one shaft to another shaft which are non
intersecting and their axis are normally right angles
to each other.
• Worm and worm gears is special case of spiral gear
in which shaft angle is 90 degree.
• Worm is threaded screw while worm gear is
toothed gear.
• Generally worm have 1 to 8 teeth.

18. • Worm gears are used when large gear reductions are
needed. It is common for worm gears to have
reductions of 20:1, and even up to 300:1 or greater
• Worm gears are used widely in material handling and
transportation machinery, machine tools,
automobiles etc

20. • Gear train is combination of gear which is used to
transmit motion and power from one shaft to
another.
• a Gear train is also called as train of toothed
wheels.
• A gear train is two or more gear working together
by meshing their teeth and turning each other in a
system to generate power and speed
• It reduces speed and increases torque
• Gear train may use spur, bevel, or spiral gears

21. Application
• Gear trains are used to either speed up or
stopped down the speed of the driven shaft .
• Gear trains are widely used in modern machines
like, in automobile ,ships, clocks, watches, lathes,
milling and planning machines etc.

22. Types of gear trains are following ,
1. Simple gear train
2. Compound gear train
3. Reverted gear train
4. Epicyclic gear train

23. • A series of gears capable to receiving and
transmitting motion from one shaft to another
shaft is called simple gear trains.
• The most common of the gear train is the gear
pair connecting parallel shafts. Gear axes are fixed
to frame.
• Two end gears always moves in opposite direction
s.
• All odd number gears move in one direction and
even number gears moves in opposite direction.

24. A simple gear train is one in which each shaft carries
only one gear. The velocity ratio (sometimes called
train ratio) of this gear-set is found by expanding
equation:
Consider a simple gear train with four gears in
series. The expression for this simple train's velocity
ratio is:
mv = (-N1/N2) (-N2/N3) (-N3/N4) = -N1/N4
“Simple Gear Trains are limited to a ratio of about10: 1”.
Gear ratio =
Number of Driver Gear Teeth
Number of Driven Gear Teeth

26. • A series of gears are connected in such way that
two or more gears rotate about an axis with
same angular velocity, it is known as compound
gear trains.
• In compound gear trains intermediate shaft
carries two gears.
• For large velocities, compound arrangement is
preferred
• Compound gear trains are used in headstock of
lathe machine.

27. When there are more than one gear on a shaft, it is
called a compound train of gear. Since the idle gears,
in a simple train of gears do not effect the speed ratio
of the system. But these gears are useful in bridging
over the space between the driver and the driven.
To get a train ratio of greater than about 10:1 with
spur, helical, or bevel gears (or any combination
thereof) it is necessary to compound the train.
Gear ratio =
Number of Driver Gear Teeth
Number of Driven Gear Teeth
mv = (-N1/N2)x(-N3/N4)x(-N5/N6)
“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.”

29. The gearing of a machine tool is shown in Figure. The motor shaft is connected to gear A
and rotates at 975 r.p.m. The gear wheels B, C, D and E are fixed to parallel shafts rotating
together. The final gear F is fixed on the output shaft. What is the speed of gear F ? The
number of teeth on each gear are as given below :
No. of teeth on each Gear,
TA = 20, TB = 50, TC = 25, TD = 75, TE = 26, TF = 65
Solution-
NA = 975 r.p.m. ;
NF = ?
mv = NA /NB x NC /ND x NE /NF = NA /NF
Or
NA /NF = TB /TA x TD /TC x TF /TE
So,
NA /NF = 50 /20 x 75 /25 x 65 /26
 NF = NA /(18.75)
NF = 975 /(18.75)
NF = 52 r.p.m. Ans