Product Manual

has been shown to result in long life, smooth operation, and noise levels
acceptable for industrial environments.
The number of threads in the worm shaft, related to the number of teeth
in the worm gear, determine the speed reduction ratio. Single-reduction
worm gear reducers are commonly available in ratios from approximately
5:1 through 60:1. A 5:1 ratio means that motor input of 1750 RPM is
converted to 350 RPM output. A 60:1 ratio brings output RPM of the same
motor to 29 RPM. Greater speed reductions can be achieved through
double-reduction – meaning two gear reducers coupled together.
The flip side of “geared-down” speed is “geared-up” torque. For the
majority of gear reducers in North America, output torque is expressed
in inch-pounds or foot-pounds. Outside of North America, the metric
unit of torque, newton-meter, is most common. Output speed and out-
put torque are the key application criteria for a gear reducer.
Parallel-Shaft Gear Reducers
Parallel-shaft units are typically built with a combination of helical
and spur gears in smaller sizes, and all helical gears in larger sizes.
Helical gears, which have teeth cut in helixes to maximize gear-to-gear
contact, offer higher efficiencies and quieter operation – though at a
correspondingly higher cost than straight-tooth spur gears.
Single-reduction speed ratios are far more limited in parallel-shaft
reducers than in right-angle worm reducers, but multiple reductions (or
gear stages) fit easily within a single parallel-shaft reducer housing. As a
result, the availability of higher ratios is usually greater in parallel-shaft
reducers and gearmotors; ratios as high as 900:1 are common in small
gearmotors.
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Combination of spur and helical
gears can be seen in this cutaway
view of a sub-fractional horsepower
parallel-shaft gearbox. Note multiple
gear stages.