1-2 Characteristics of GearsSpur Gear
The teeth are straight and parallel to the shaft axis. Transmits power and motion between rotating two parallel shafts.
- Easy to manufacture
- There are no axial force
- Relatively easy to produce high-quality gears
- The most common type of gear
- Transmission components
The teeth are twisted oblique to the gear axis.
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
- Has higher strength compared with a spur gear
- More effective in reducing noise and vibration when compared with a spur gear
- Gears in mesh produce thrust forces in the axial direction
- Transmission components, automobile, speed reducers, etc.
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.
- Changes a rotary motion into a rectilinear motion and vice versa
- A transfer system for machine tools, printing presses, robots, etc.
An annular gear having teeth on the inner surface of its rim.
The internal gear always meshes with an external gear.
- When meshing two external gears, the rotation occurs in the opposite directions. When meshing an internal gear with an external gear the rotation occurs in the same direction
- Care should be taken with regard to the number of teeth on each gear when meshing a large (internal) gear with a small (external) gear, since three types of interference can occur
- Usually internal gears are driven by small external gears
- Allows for a compact design of the machine
- Planetary gear drive of high reduction ratios, clutches, etc.
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
Straight Bevel Gear
A simple form of bevel gear having straight teeth which, if extended inward, would come together at the intersetion of the shaft axes.
- Relatively easy to manufacture
- Provides reduction ratios up to approx. 1:5
- Machine tools, printing presses, etc. Especially suitable for use as a differential gear unit
Spiral Bevel Gear
Bevel gear with curved, oblique teeth to provide gradual engagement and larger contact surface at a given time than an equivalent straight bevel gear.
- 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
- Automobiles, tractors, vehicles, final reduction gearing for ships. Especially suitable for high-speed, heavy load drives
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.
A helical gear that transmits power from one shaft to another, nonparallel, nonintersecting shaft.
- Can be used as a speed reducer or as a speed increaser
- Due to sliding contact, has higher friction
- Not suitable for transmission of high horsepower
- Driving gear for automobile. Automatic machines that require intricate movement
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.
- Provides large reduction ratios for a given center distance
- Quiet and smooth meshing action
- It is not possible for a worm wheel to drive a worm unless certain conditions are met
- Speed reducers, antireversing gear devices making the most of its self-locking features, machine tools, indexing devices, chain blocks, portable generators, etc.
Related links :
Gear Types and Characteristics