2. SPUR GEARS
❖ Most commonly used gears.
❖ Simplest form of gears.
❖ Teeth are parallel to the face of the gears.
❖ Transmits power between parallel shafts.
❖ Least expensive.
TYPES:-
❖ Internal Spur Gears.
❖ External Spur Gears.
3. GEAR TERMINOLOGY
❖ Pinion: A pinion is smaller of the two mating gears.
❖ Gear: A gear is larger of the two mating gears.
❖ Velocity ratio: (i) Velocity ratio is the ratio of angular
velocity of the driving gear to the angular velocity of the
driven gear. It is also called the speed ratio.
❖ Pitch surface: The pitch surfaces of the gears are
imaginary planes, cylinders or cones that roll together
without slipping.
❖ Pitch circle: The pitch circle is the curve of intersection
of the pitch surface of revolution and the plane of
rotation. It is an imaginary circle that rolls without
4. GEAR TERMINOLOGY
slipping with the pitch circle of a mating gear. The pitch
circle of a pair of mating gears are tangent to each
other.
❖ Pitch circle diameter: The pitch circle diameteris the
diameter of pitch circle. The size of the gear is usually
specified by pitch circle diameter. It is also called 'pitch
diameter. The pitch circle diameter is denoted by d'.
❖ Pitch point: The pitch point is a point on lineof centers
of two gears at which two pitch circles of mating gears
are tangent to each other.
❖ Top land: The top land is the surface of the top of the
gear tooth.
❖ Bottom land: The bottom land is the surface of the gear
between the flanks of adjacent teeth.
5. GEAR TERMINOLOGY
❖ Involute: An involute is a curve traced by a point on a line as the line rolls without slipping
on a circle.
❖ Base circle: The base circle is an imaginary circle from which the involute curve of the
tooth profile is generated. The base circle of two mating gears are tangent to the pressure
line.Pitch point The pitch point is a point on line of centers of two gears at which two pitch
circles of mating gears are tangent to each other.
❖ Addendum circle: The addendum circle is an imaginary circle that borders the tops of gear
teeth in the cross-section
❖ Addendum: The addendum is the radial distance between pitch and the addendum circles.
Addendum indicates the height of tooth above the pitch circle.
❖ Dedendum circle: The dedendum circle is an imaginary circle that borders the bottom of
spaces between teeth in the cross-section. It is also called root circle.
❖ Dedendum: The dedendum is the radial distance between pitch and the dedendum circles.
6. GEAR TERMINOLOGY
❖ Clearance: The clearance is the amount by which dedendum of given gear exceeds
adendum of mating tooth.
❖ Face of tooth: The surface of gear tooth between the pitch cylinder and addendum
cylinder.
❖ Flank of Tooth: The surface of the gear tooth between the pitch cylinder and the root
cylinder is called flank of the tooth.
❖ Face Width: Face width is the width of the tooth measured parallel to the axis.
❖ Fillet Radius: The radius that connects the root circle to the profile of the tooth is called
fillet radius.
❖ Circular Tooth: The length of the arc on the pitch circle subtending a single gear tooth is
called circular tooth thickness. Theoretically, circular tooth thickness is half of the circular
pitch.
❖ Tooth Space: The width of the space between two adjacent teeth measured along the
pitch circle is called the tooth space. Theoretically, tooth space is equal to circular tooth
thickness or half the circular pitch.
❖
7. GEAR TERMINOLOGY
❖ Working Depth: The working depth is the depth of engagement of two gear teeth, that is,
the sum of their addendums.
❖ Whole Depth: The whole depth is the total depth of the tooth space, that is, the sum of the
addendum and dedendum. Whole depth is also equal to working depth plus clearance.
❖ Centre Distance: The centre distance is the distance between centres of pitch circles of
mating gears. It is also the distance between centres of base circles of mating gears.
❖ Pressure Angle: The pressure angle is the angle which the line of action makes with the
common tangent to the pitch circles. The pressure angle is also called the angle of
obliquity. It is denoted by a.
❖ Line of Action: The line of action is the common tangent to the base circles of mating
gears.The contact between the involute surfaces of mating teeth must be on this line to
give a smooth operation.The force is transmitted from the driving gear to the driven gear
on this line.
❖ Contact Ratio: The number of pairs of teeth that are simultaneously engaged is called
contact ratio.
8. GEAR TERMINOLOGY
❖ Circular Pitch: The circular pitch (p) is the distance measured along the pitch circle
between two similar points on adjacent teeth.
❖ Diametral Pitch: The diametral pitch (P) is the ratio of the number of teeth to the pitch
circle diameter.
❖ Module: The module (m) is defined as the inverse of the diametral pitch.
9. MATERIALS
General Materials used for Spur Gear Manufacturing:-
❖ Steel
❖ Cast Iron - Gray cast iron and Nodular and ductile cast iron( Good casting
property )
❖ Stainless Steel
❖ Aluminum
❖ Bronze
❖ Nylon
❖ Non-metals -Plastic, reinforced laminates(noiseless operation, cheaper)
10. Why we chose cast iron ?
● High tensile strength to prevent failure against static loads.
● High endurance strength to withstand dynamic loads.
● Low cost
● High availability
● Good manufacturing
● Low coefficient of friction
12. MANUFACTURING OF SPUR GEARS
There are a number of methods to manufacture gears. They include casting,
blanking and machining. However, power transmitting gears are made of steel and
made by the following methods:
❖ Milling
❖ Rack generation
❖ Hobbing
❖ Gear shaper method
The hobbing process accounts for the manufacture of a major quantity of gears
that are used for power transmission.
13. GEAR FORMING
Gear cutting by forming:
In this processes, the cutter used has the same form as the space between the
teeth to be cut. The cutters used for this purpose on planer and shaper are single
point tools, on milling machine a revolving multi tooth tool and on broaching
machine a broach.
❖ Gear Milling
❖ Broaching
❖ Shaping,planing,slotting
❖ Parallel multi-teeth shaping(fast production)
14. GEAR MILLING
Gear milling:
The usual practice in gear milling is to mill
one tooth space at a time, after which the
blank is indexed to the next cutting position.
Individual tooth spacing are created by a
rotating multi edge cutter having a
cross-section similar to that of the generated
teeth.After cutting each space, the cutter
returns to its original position, and the gear
blank is indexed for the next cut.
15. GEAR MILLING
Gear forming on milling machines (and shapers) has the
following characteristics:
❖ Advantages:General purpose equipment and
machines are used.Comparatively simple setup is
needed.Simple and cheap cutting tools are used.It
is suitable for piece and small size production.
❖ Drawbacks:It is an inaccurate process due to
profile deviations and indexing errors.Low
production capacity due to the idle time loss in
indexing, approaching, and withdrawalof the tool.
16. GEAR GENERATION
Gear cutting by generationThis technique is based on the fact that two involute
gears of the same module and pitch mesh together—the WP blank and the cutter.
So this method makes it possible to use one cutting gear for machining gears of
the same module with a varying number of teeth.Gear generation methods are
characterized by their higher accuracy and machining productivity than gear
forming.
❖ Gear shaper process
❖ Rack generation process
❖ Hobbing process
17. RACK GENERATION
Gear cutting using rack type cutter: Gear shaping is
performed by a rack cutter with 3–6 straight teeth. The
cutters reciprocate parallel to the work axis when cutting
spur gears, and parallel to the helix angle when cutting
helical gears. In addition to the reciprocating action of
the cutter, there is synchronized rotation of the gear
blank with each stroke of the cutter, with a
corresponding advance of the cutter in a feed
movement.
18. GEAR SHAPER PROCESS
Gear shaper process:In this process, a pinion shaped cutter is used, which is
mounted with its axis vertical and is reciprocate up and down. This process is the
most versatile of all gear cutting processes. Also, the cutter and the gear blank
both are rotated slowly about their own axis.
19. HOBBING
Gear hobbing: Hobbing is a gear generation method most widely used for cutting
teeth in spur gears, helical gears, worms, worm wheels, and many special forms.
In this process, the gear blank is rolled with a rotating cutter called hob. A gear
hob looks like a worm.
20. APPLICATIONS OF SPUR GEAR
In mechanical systems where we’ll require simple design, more efficient power
transfer, and low speed applications where noise does not matter, we should go
for spur gears. Spur gears have a wide range of applications.
They are used in:
❖ Metal cutting machines
❖ Power plants
❖ Marine engines
❖ Mechanical clocks and watches
❖ Fuel pumps
❖ Washing Machines
❖ Gear motors and gear pumps
❖ Rack and pinion mechanisms
❖ Material handling equipments
❖ Automobile gear boxes
❖ Steel mills
21. REFERENCES
❖ V B BHANDARI
❖ http://www.psnacet.edu.in/courses/Mechanical/Machining/lecture4.pdf
❖ https://sciencing.com/uses-spur-gears-7508417.html
❖ https://www.quora.com/What-are-the-differences-between-gear-milling-an
d-gear-hobbing
❖ https://science.howstuffworks.com/transport/engines-equipment/gear2.ht
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