How Gears
Work
by Karim Nice
Helical Gears
The teeth on helical gears are cut at an angle to the face
of the gear. When two teeth on a helical gear system engage, the
contact starts at one end of the tooth and gradually spreads as
the gears rotate, until the two teeth are in full engagement.
Photo courtesy Emerson Power Transmission Corp.
Figure 3. Helical gears
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This gradual engagement makes helical gears operate much more smoothly
and quietly than spur gears. For this reason, helical gears are
used in almost all car transmissions.
Because of the angle of the teeth on helical gears, they create
a thrust load on the gear when they mesh. Devices that use helical
gears have bearings that can support this thrust load.
One interesting thing about helical gears is that if the angles
of the gear teeth are correct, they can be mounted on perpendicular
shafts, adjusting the rotation angle by 90 degrees.
Photo courtesy Emerson Power Transmission Corp.
Figure 4. Crossed helical gears
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