“IN THE NAME OF ALLAH, THE MOST BENEFICENT,
THE MOST MERCIFUL”
Gear
A gear is a rotating machine part having cut
teeth, or cogs, which mesh with another toothed
part in order to transmit torque
Introduction
 Gears are the most common means used
for power transmission
 They can be applied between two shafts
which are
 Parallel
 Collinear
 Inclined at any arbitrary angle
Why we use gears
In order to avoid the slipping, a number of projections
(called teeth) are provided on the periphery of the
wheel which will fit into the corresponding recesses
on the periphery of the other wheel.
A friction wheel with the teeth cut on it is known as
toothed wheel or gear.
Gear advantages
 It transmits exact velocity ratio
 It may be use to transmit large power
 It has high efficiency
 It has reliable(easy) services
Gear disadvantages
 It costs expensive to manufacture
 Any type of error may cause vibrations and noise
 It requires suitable lubricant and reliable method of
applying it, for proper operation of gear drives
(a) Parallel
(b) Intersecting
(c) Non-intersecting and non-parallel.
1)PARALLEL:
These gears have teeth
parallel to the axis of the wheel.
2)INTERSECTING:
These gears are called
bevel gears and the
arrangement is known as
bevel gearing.
The bevel gears
have their teeth inclined to the face of the bevel, in which case they
are known as helical bevel gears.
3)Non intersecting & non parallel:
A gear having teeth in such a way that its
axis of rotation does not cross the length of
teeth when extended
Nomenclature
It is the circle made by joining those points where two
meshed teeth release each other
2. Pitch circle diameter.
It is the diameter of the pitch circle. The size of the gear is
usually specified by the pitch circle diameter. It is also known as
pitch diameter
3. Pitch point.
Point where the line of action crosses a line joining the
two gear axes
4. Pitch surface.
It is the surface of the rolling discs which the meshing gears have
replaced at the pitch circle
5. Pressure angle or angle of obliquity.
It is the angle between the common normal to two gear teeth at the
point of contact and the common tangent at the pitch point.
6. Addendum.
It is the radial distance of a
tooth from the pitch circle to
the top of the tooth
7. Dedendum.
It is the radial distance of a tooth from the pitch circle to the bottom
of the tooth
8. Addendum circle. It is the circle drawn through the top of the
teeth and is concentric with the pitch circle.
9. Dedendum circle. It is the circle drawn through the bottom of the
teeth. It is also called root circle.
10. Circular pitch. It is the distance measured on the circumference
of the pitch circle from a point of one tooth to the corresponding
point on the next tooth.
Mathematically,
Circular pitch = D/T
where D = Diameter of the pitch circle, and
T = Number of teeth on the wheel.
11.Diametral pitch.
It is the ratio of number of teeth to the pitch circle diameter in
millimetres.
Mathematically,
Diametral pitch=T/D
12.Module.
It is the ratio of the pitch circle diameter in millimeters to the
number of teeth.
It is usually denoted by m. Mathematically,
Module, m = D /T
13. Clearance.
It is the radial distance from the top of the tooth to the bottom of the
tooth, in a meshing gear. A circle passing through the top of the
meshing gear is known as clearance circle.
14. Total depth.
It is the radial distance between the addendum and the dedendum
circles of a gear. It is equal to the sum of the addendum and
dedendum.
15. Working depth.
It is the radial distance from the addendum circle to the clearance
circle.
16. Tooth thickness.
It is the width of the tooth measured along the pitch circle.
17. Tooth space .
It is the width of space between the two adjacent teeth measured
along the pitch circle.
18. Backlash.
It is the difference between the tooth space and the tooth thickness,
as measured along the pitch circle.
19. Face of tooth.
It is the surface of the gear tooth above the pitch surface.
20. Flank of tooth.
It is the surface of the gear tooth below the pitch surface.
21. Top land.
It is the surface of the top of the tooth
22. Face width.
It is the width of the gear tooth measured parallel to its axis.
23. Profile.
It is the curve formed by the face and flank of the tooth.
24. Fillet radius.
It is the radius that connects the root circle to the profile of the
tooth.
25. Path of contact.
It is the path traced by the point of contact of two teeth from the
beginning to the end of engagement.
Angular frequency
 Measured in radians
per second.
 1RPM = π / 30
rad/second
 It is denoted by “ω”
Gear, wheel
The larger of two interacting gears
Pinion
The smaller of two interacting gears
Line of action, pressure line
Line along which the force between two meshing gear teeth is directed.
Axis
 Axis of revolution of the gear; center line of the
shaft
Application of Gear
· Defense
· Fertilizer Industry
· Food Processing
· Marine
· Paper
· Turbine Plant
· Aluminum
· Chemical
· Grinding Mills
· Hot and Cold Rolling
· Movable bridge
· Petroleum
· Plastics
· Rubber
· Sugar
· Stamping Presses
· Wind Turbines
· Surface Mining
· Petrochemical
· Rubber Plants
· Sponge Iron
· Material Handling
· Earth Moving Industry
· Aviation Industry
· Cement Plant
· Coal Plants
· Construction Machinery
· Elevator Industry
· Medical Industry
· Micro Assembling
· Power Industry
· Printing Industry
· Railway Industry
· Steel Plants
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 metallic or nonmetallic materials
 The metallic gears with cut teeth are commercially
obtainable in cast iron, steel and bronze
 The nonmetallic materials like wood, raw hide, compressed
paper and synthetic resins like nylon are used for gears,
especially for reducing noise.
Gear Materials
 The cast iron gears with cut teeth may be employed,
where smooth action is not important.
 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
TYPES OF GEARS










SPUR GEAR
BEVEL GEAR
External and internal gear
WORM GEAR
DIFFERENTIAL GEAR
RACK GEAR
PINION
IDLER GEAR
RATCHET
PLANETARY GEAR
DISCRIBTION
SPUR GEAR:
A gear wheel
having radial
teeth parallel to
the axle.
Application Spur Gear
 Spur Gear and Plastic Spur Gears used in a film
winding component.
 Spur Gears used in automatic packing machine.
 Spur Gears are used in the film-cutting
component.
BEVEL GEAR

A gear wheel
meshed with
another so that
their shafts are at
an angle less than
180 degrees ( LEGO
size 90 degree with
14 teeth )
Application of Bevel gear
it is used in grain mill.
 it is used in power plant.
 it is used in Railway track inspection
machine
 Bevel gear used in floodgate.

1.External vs. internal gears
External Gear
An external gear is one with the teeth formed on the
outer surface of a cylinder or cone.
internal gear
internal gear is one with the teeth
formed on the inner surface of a cylinder
or cone.
 (hub
gear) internal gear used in bicycle
and bikes.
 internal
gear used in internal gear
pumps.
 used
in wind turbine generator
DEFINITION OF WORM GEAR

WORM GEAR: A
short rotating screw
that meshes with
the teeth of another
gear. As a worm
gear is an inclined
plane, it will be the
driving gear in most
cases ( THE LAW
OF THE WORM! ).
Application of worm gear
worm drive used in controlling a gate
 Packaging Industries (Machines)
 Material Handling Equipments
 Food Processing Machines
 Widely in Conveyor Systems

DEFINITION OF RACK GEARS
 RACK GEAR: A
toothed bar into
which a "pinion," (
worm gear spur etc )
meshes. ( LEGO® size
1 x 4 with 10 teeth )
DEFINITION OF PINION GEAR
 PINION: A small cogwheel, the teeth
of which fit into those of a larger
gearwheel or those of a rack.
DEFINITION OF IDLER GEAR
IDLER GEAR: A gear
wheel placed between
two other gears to
transmit motion from
one to the other. It does
not alter the speed of
the output, but it does
alter the direction it
turns. ( ODD number
=reverse rotation,
EVEN number = same
rotation )

DEFINITION OF RATCHET

RATCHET: A toothed
wheel or bar that
catches and holds
a PAWL, which thus
prevents backward
movement.

The ratchet is really another form of gearing.
Unlike gears which can be used to speed up or
slow down movement, the ratchet can only be
used to slow things down and it happens in a
very jerky manner. Below and opposite is an
explanation of how they work.
Definition of Pawl
PAWL
 A mechanical device
allowing rotation in
only one direction.
Definition of Planetary gear
 PLANETARY GEAR:A device allowing
several gears to "orbit" about others ( very
handy for robot turntables )

Planetary Gears are the latest
type and used in Robotics
Gear Manufacturing
Hobbing
 Hobbing is a machining process for
making gears, splines, and sprockets on a hobbing
machine, which is a special type of milling machine.
The teeth or splines are progressively cut into the
workpiece by a series of cuts made by a cutting
tool called a hob. Compared to other gear forming
processes it is relatively inexpensive but still quite
accurate, thus it is used for a broad range of parts and
quantities.
 It is the most widely used gear cutting process for
creating spur and helical gears\and more gears are cut
by hobbing than any other process since it is relatively
quick and inexpensive.
 Gear Shaping Operation - Gear shaping process
makes use of a hardened pillion as a cutter,
ground with top rake and clearance. Referring to,
gear shaping cutter 1 receives reciprocating
movement (in the direction of arrow 1) which is
the principal movement. The cutter reciprocates
like the cutting tool in a standard shaper but at a
rate of 50 to 450 strokes per minute.
1.backlash
Defects in gear
 In mechanical engineering, backlash, sometimes
called lash or play, is clearance between mating components,
sometimes described as the amount of lost motion due to
clearance or slackness when movement is reversed and contact is
re-established. For example, in a pair of gears, backlash is the
amount of clearance between mated gear teeth.
 Theoretically, the backlash should be zero, but in actual practice
some backlash must be allowed to prevent jamming. It is
unavoidable for nearly all reversing mechanical couplings,
although its effects can be negated. Depending on the
application it may or may not be desirable. Reasons for requiring
backlash include allowing for lubrication, manufacturing
errors, deflection under load and thermal expansion.
Problem#1
A helical cast steel gearwith 30 helix angle has to transmit 35kW
at 1500r.p.m.If the gear has 24 teeth and the necessary module is
6mm.If tangetial tooth load is 3100N.
Determine
1.the pitch diameter and face width for 20 fulldepth teeth.
The static stress for cast steel may be taken as 56Mpa.The width
of facemay be taken as 3 times the normal pitch.
2.What would be the end thrust on the gear?
The tooth factor for 20 full depth involute gear may be taken as
.154-(.912/Te), where Te represents the equivalent number of
teeth.
Problem#2
A triple threaded worm has teeth of 6mmmodule and
pitch circle diameter of 50mm.Ifthe worm gear has 30
teeth of 14.5 and the coefficient of friction of the worm
gearing is .05
Find
1.The lead angle of the worm,
2.Velocity ratio,
3.Centre distance