Changing Direction with Gears
In this presentation you will:
 identify how gears can be used to change the axis of
rotation in a mechanism
Changing Direction with Gears
In this presentation you will
discover the different types of
gears that are used to change
the axis of rotation in a
mechanical system.
You will see different types of
bevel gears and identify where
they are most likely to be used.
You will also see how rack-andpinion and worm gears operate.
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Changing Direction with Gears
Bevel Gears
Bevel gears are primarily used
to transfer power between
intersecting shafts, where the
axis of rotation of two shafts are
at 90 degrees to each other.
The teeth of these gears are
formed on a conical surface.
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Changing Direction with Gears
Types of Bevel Gears
Standard bevel gears have teeth
that are cut straight. The teeth
point toward the apex of the cone
on which they are machined.
Apex of the cone
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Changing Direction with Gears
Spiral bevel gears have teeth that
have been cut on a curve.
The larger surface contact area
makes for a smoother, quieter
running system, much like helical
gears.
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Changing Direction with Gears
Hypoid bevel gears are a special type of spiral gear that will allow nonintersecting, non-parallel shafts to mesh.
Parallel shafts
Intersecting shafts
Hypoid gears are stronger, operate more quietly, and can be used for higher
reduction ratios than spiral bevel gears.
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Changing Direction with Gears
Question 1
Bevel gears are primarily used to transfer power between
parallel shafts. Is this true or false?
Answer True or False.
Changing Direction with Gears
Bevel Gear Applications
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.
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.
Hypoid bevel gears are also used in
high performance applications, but are
more expensive to produce. They are
typically used in transmission systems.
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Changing Direction with Gears
Question 2
Which type of bevel gear is typically used in low speed applications?
A) Standard
B) Spiral
C) Hypoid
Changing Direction with Gears
Worm gears
Worm Gears
Worm gears resemble screws,
and can be used to drive gear
wheels (spur gears or helical
gears).
They allow two non-intersecting
shafts at right angles to mesh with
each other.
Spur gears
Helical gears
Worm drives provide a large
reduction in speed. For one rotation
of the worm gear, the gear wheel
moves by a distance of one tooth.
They are typically used in
gearboxes, where large
reductions in speed, for example
300:1, are required.
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Changing Direction with Gears
Question 3
A worm gear is driving a gear wheel that has 20 teeth. How far
will the gear wheel turn, if the worm gear rotates 5 times? Enter
your answer in degrees.
Enter your answer and press SEND.
Changing Direction with Gears
Rack-and-pinion Gears
The rack-and-pinion is typically used
to turn rotary motion into linear
(straight line) motion, or vice versa.
Pinion gear
Racks are simply straight gears.
The pinion is usually a spur gear
that meshes with the rack.
Rack gear
As the pinion turns, the rack
moves in a lateral direction.
The rack-and-pinion is typically used
in automotive steering systems.
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Changing Direction with Gears
Question 4
The rack-and-pinion is typically used in automotive steering
systems, and converts rotary motion into linear motion. Is this
true or false?
Answer True or False.
Changing Direction with Gears
Gear Ratios
Driven
The gear ratio of a bevel gear system is calculated
in the same way as for a simple gear train.
Gear ratio = Number of Driven Gear Teeth
Number of Driver Gear Teeth
With a worm system, the worm
gear is equivalent to a single tooth
gear.
Driver
Ratio =
100
˙
= 1.6:1
60
If the spur gear has 90 teeth, then
the gear ratio is:
90
= 90:1
1
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Changing Direction with Gears
Summary
You should now be aware of:
 which types of gear can change the
axis of rotation in a mechanism
 how to calculate gear ratios for bevel
gears and worm gear systems
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