14.2 MOTION/FORCE TRANSMISSIONS

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14.2.1 Gears

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Gears are generally round or linear sets of teeth for transmitting forces or motions.

Different combinations of gears will allow conversions of forces, motions and directions.

Different types of gears are,

- spur

- internal

- helical

- herringbone

- bevel

- hypoid

- worm

- rack and pinion

14.2.1.1 - Spur Gears

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transmit power between parallel shafts

have straight teeth parallel to axis of rotation

used for slow/moderate speeds

when two of these gears are meshed, the larger is the gear, the smaller is the pinion

14.2.1.2 - Internal Gears

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transmission between parallel shafts

require less space

better meshing/more contact between gears.

14.2.1.3 - Helical Gears

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Gears with teeth on an angle.

can convert rotary motion to rotary motion on a non-parallel shaft.

a tooth does not suddenly engage/disengage fully, so noise and vibration are reduced.

also, more than one tooth is typically in contact, so the strength is increased.

these gears often generate longitudinal forces that require thrust bearings.

14.2.1.4 - Herringbone Gears

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Looks like a helical gear, but it looks as if a second helical gear with a reverse helix has been attached.

Similar to helical gears, except that thrust bearings are not required.

14.2.1.5 - Bevel Gears

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Transmit rotations to another axis perpendicular to the first.

These gears look like spur gears, but with a taper.

When the two gears are the same size they are miter gears.

for non-90° intersections, the gears are called angular bevel gears.

the rotational axes of these gears intersect.

14.2.1.6 - Hypoid Gears

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Like bevel gears, but with helical teeth

the gears are often offset also (the ases of rotation do not intersect)

these gears are commonly used in the auto industry.

14.2.1.7 - Worm Gears

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The worm is a helical gear with one or more threads.

The worm gear is typically a straight tooth gear that is turned by the worm.

This combination is used to convert rotation to a perpendicular rotation, and reduce the speed.

14.2.1.8 - Rack and Pinion

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A rotating spur gear drives a linear rack of teeth.

this combination converts a rotation to a linear motion.