Law of toothed gearing – Involutes and cycloidal tooth profiles –Spur Gear terminology and definitions –Gear tooth action – contact ratio – Interference and undercutting. Helical, Bevel, Worm, Rack and Pinion gears

1. GEARS
UNIT-4

2. Introduction
• Gears are toothed wheels used for
transmitting motion and power from one
shaft to another

3. Advantages of Gear Drive
• Since there is no slip, so exact velocity ratio is obtained.
• Larger power can be transmitted.(Compare to Belt & Chain)
• Its more efficient (up to 99%)
• Its require less space

4. Disadvantages of Gear Drive
• Need special machines and tools for manufacturing Gear.
• High maintenance cost
• Chances of vibration & Noise in operation
• It require precise alignment of shafts for power
transmission.

5. TYPES OF GEARS
According to the position of axes of the shafts.
a. Parallel
1.Spur Gear
2.Helical Gear
3. Herringbone Gear
4.Rack and Pinion
b. Intersecting
Bevel Gear - Straight bevel Gear
- Spiral bevel Gear
c. Non-intersecting and Non-parallel
worm and worm gears

6. Spur Gear
1.Teeth is parallel to axis of rotation
2.Transmit power from one shaft to another parallel shaft
3.Used in Electric screwdriver, oscillating sprinkler, windup
alarm clock, washing machine and clothes dryer

7. External and Internal spur Gear…

8. Helical Gear
• In which the teeth are inclined to the axis
• This gradual engagement makes helical gears
operate much more smoothly and quietly than
spur gears

9. Herringbone gears
• In which the teeth are
inclined to the axis.
• The double helical gears are
known as herringbone gears.
• Herringbone gears are
mostly used on heavy
machinery.

10. Rack and pinion
• Rack and pinion gears
convert linear motion
into rotary motion.
• A perfect example of this
is the steering system on
many cars

11. Bevel gears
• The two non-parallel or intersecting , but coplanar
shafts connected by gears are called bevel gears
• The teeth on bevel gears can be straight, spiral or
hypoid
• locomotives, marine applications, automobiles,
printing presses, cooling towers, power plants, steel
plants, railway track inspection machines, etc.

12. Straight and Spiral Bevel Gears
Straight Bevel Gear Spiral Bevel Gear

13. WORM AND WORM GEAR
• Worm and worm wheel, also known as worm gears, are
used to transmit power from one shaft to another which
are non-intersecting and their axes are normally right
angles to each other.
• Worm gears are used widely in material handling and
transportation machinery, machine tools, automobiles etc
• Advantage:
• The operation is smooth and quit.
• Disadvantage:
• The efficiency is low and they are costly.
• The power transmitting capacity is also low.

14. WORM AND
WORM GEAR

15. According To The Peripheral Velocity
Of The Gears
a) Low velocity: the gears having velocity less
than 3m/s.
b) Medium velocity: gears having velocity
between 3 and 15 m/s.
c) High velocity: more than 15m/s

16. NOMENCLATURE OF SPUR
GEARS

17. Pressure Angle
• Pressure Angle:
– Angle between the Line of Action and a line perpendicular
to the Line of Centers.

18. Terms Used In Gears
Addendum: The radial distance between the Pitch Circle
and the top of the teeth.
 Dedendum: The radial distance between the bottom of
the space between teeth and the pitch circle.
Clearance: The distance between the top of a tooth and
the bottom of the space into which it fits on the meshing
gear.
Whole Depth— addendum + dedendum + Clearance
Working Depth — addendum + dedendum

19. Backlash
• Backlash:
The difference between the circle thickness of
one gear and the tooth space of the mating
gear.

20. Diametral pitch (Pd)&Module (m)
• Diametral pitch (Pd): The number of teeth divided by the
pitch diameter. That is,
Where
Pd = diametral pitch
N = number of teeth
D = pitch diameter
• Module (m): Pitch diameter divided by number of teeth. The
pitch diameter is usually specified in inches or millimeters; in
the former case the module is the inverse of diametral pitch.
m = D/N
D
N
Pd 

21. Velocity Ratio Of Gear Drive
d = Diameter of the wheel
N =Speed of the wheel
ω = Angular speed
velocity ratio (n) =
2
1
1
2
1
2
d
d
N
N





22. Circular pitch (Pc)
• It’s a distance measured along the
circumference of pitch of the pitch circle from
a point on one tooth to the corresponding on
the adjacent tooth

23. Gear Ratio

24. Fundamental Law of Gearing
• The angular velocity ratio between the gears in
a gear-set must remain constant between the
two meshing gears.

25. Law of Gearing

26. Proof -

27. .

28. .

29. .

30. Gear Materials
• The material used for the manufacture of gears depends upon
the strength and service conditions like wear, noise etc. The
gears may be manufactured from
1. metallic
2. non-metallic materials.
• Metallic:
• The metallic gears with cut teeth are commercially obtainable
in
 cast iron,
 steel and
 bronze.

31. Metallic materials
• The cast iron is widely used for the manufacture
of gears due to its good wearing properties,
excellent machinability and ease of producing
complicated shapes by casting method.
• The steel is used for high strength gears and steel
may be plain carbon steel or alloy steel.
• The phosphor bronze is widely used for worm
gears in order to reduce wear of the worms which
will be excessive with cast iron

32. Non Metallic Materials
• The non metallic materials like
 wood,
 raw hide,
 compressed paper and
 synthetic resins like nylon are used for
gears, especially for reducing noise.

33. Gear Tooth Failure