T-28
2.7.2 Intersecting Axes Gears
1. Straight Bevel Gear
This is a gear in which the teeth have tapered
conical elements that have the same direction as the
pitch cone base line (generatrix). The straight bevel
gear is both the simplest to produce and the most
widely applied in the bevel gear family.
2. Spiral Bevel Gear
This is a bevel gear with a helical angle of spiral
teeth. It is much more complex to manufacture, but
offers a higher strength and lower noise.
3. Zerol Gear
Zerol gear is a special case of spiral bevel gear.
It is a spiral bevel with zero degree of spiral angle
tooth advance. It has the characteristics of both the
straight and spiral bevel gears. The forces acting upon
the tooth are the same as for a straight bevel gear.
2.7.3 Nonparallel and Nonintersecting Axes Gears
1. Worm and Worm Gear
Worm set is the name for a meshed worm and
worm gear. The worm resembles a screw thread; and
the mating worm gear a helical gear, except that it is
made to envelope the worm as seen along the worm's
axis. The outstanding feature is that the worm offers
a very large gear ratio in a single mesh. However,
transmission efficiency is very poor due to a great
amount of sliding as the worm tooth engages with its
mating worm gear tooth and forces rotation by pushing
and sliding. With proper choices of materials and
lubrication, wear is contained and noise is low.
Fig. 2-14
Straight Bevel Gear
Fig. 2-15
Spiral Bevel Gear
Fig. 2-16
Zerol Gear
Fig. 2-17
Worm Gear
