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Characteristics of Gears

1-2 Characteristics of Gears

Spur Gear
spur gears

The teeth are straight and parallel to the shaft axis. Transmits power and motion between rotating two parallel shafts.

Helical Gear
helical gears

The teeth are twisted oblique to the gear axis.

helical gears helix angle

Helix direction (helix hand) :
The hand of helix is designated as either left or right
Right-hand and left-hand helical gears mate as a set. But they must have the same helix angle

Gear Rack
gear rack

The rack is a bar containing teeth on one face for meshing with a gear.
The basic rack form is the profile of a gear of infinite diameter.
Racks with machined ends can be joined together to make any desired length.

Internal Gear
internal gears

An annular gear having teeth on the inner surface of its rim.
The internal gear always meshes with an external gear.

Bevel Gear

bevel gears
Picture : Bevel gear, apex and pitch cone

One of a pair of gears used to connect two shafts whose axes intersect, and the pitch surfaces are cones.
Teeth are cut along the pitch cone.
Depending on tooth trace, bevel gear is classified as :
1. Straight bevel gear
2. Spiral bevel gear

  1. Straight Bevel Gear
    straight bevel gears
    A simple form of bevel gear having straight teeth which, if extended inward, would come together at the intersetion of the shaft axes.
    Features :
    • Relatively easy to manufacture
    • Provides reduction ratios up to approx. 1:5
    Applications :
    • Machine tools, printing presses, etc. Especially suitable for use as a differential gear unit
  2. Spiral Bevel Gear
    spiral bevel gears
    Bevel gear with curved, oblique teeth to provide gradual engagement and larger contact surface at a given time than an equivalent straight bevel gear.
    Features :
    • Has higher contact ratio, higher strength and durability than an equivalent straight bevel gear
    • Allows a higher reduction ratio
    • Has better efficiency of transmission with reduced gear noise
    • Involves some technical difficulties in manufacturing
    Applications :
    • Automobiles, tractors, vehicles, final reduction gearing for ships. Especially suitable for high-speed, heavy load drives
Miter Gears

miter gears
A special class of bevel gear where the shafts intersect at 90° and the gear ratio is 1:1.
It is used to change the direction of shaft rotation without change in speed.

Screw Gear
screw gears

A helical gear that transmits power from one shaft to another, nonparallel, nonintersecting shaft.

Worm Gear

worm gears
Picture : Worm, Worm Gear and Center distance

Worm is a shank having at least one complete tooth (thread) around the pitch surface and is the driver of a worm wheel.
Worm Gear (worm wheel) is a gear with teeth cut on an angle to be driven by a worm.
The worm gear pair is used to transmit motion between two shafts which are at 90°to each other and lie on a plane.

Related links :
Gear Types and Characteristics

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