Mechanical Shaft Keys for Power Transmission

Mechanical shaft keys in automotive power-transmission systems are used for transferring torque.

There are several types of shaft keys for efficient and cost-effective power transmission, including Parallel Keys, Square Keys, Rectangular Keys, Woodruff Keys, Taper and Grib-Head Keys, and Feather Keys.

Parallel keys

1. Parallel Keys, sometimes called straight keys, come in two designs – square and rectangular.
2. The key is accommodated into a slot that runs along the full length of the mechanical shaft. The Parallel Key is pressed into the key slots lined up in the shaft and component.
3. Once installed, the parallel key is held in the mounted component using a setscrew or other retainer.
4. Parallel Keys are commonly used in mechanical and automotive engineering because of their inexpensiveness, availability, and ease of installation.
5. They are mostly used for transmitting only unidirectional torques subject to lighter starting loads, or in applications that require periodic withdrawal or sliding of the hub, because multi-axial torques might cause the drive component to spin free while the key loosens and gets stuck inside the machine, causing failure.

Woodruff Keys

1. Woodruff Keys are semicircular keys that are inserted into curved slots in the shaft.
2. Unlike Parallel Keys, the design of Woodruff Keys allows them to be properly installed and fixed to the shaft.
3. However, Woodruff Keys are difficult to install.
4. But as the shaft and Woodruff Key are pressed into the component, the key tends to slip out of position.
5. Woodruff keys are relatively short and cannot carry the same load as longer keys, and hence are used mostly in light-duty applications and mounting taper-bored components onto tapered shaft ends.
6. Mounting two or more Woodruff Keys in line to carry heavier loads might prove expensive and cumbersome.
7. They also require special key-cutting tools for their fabrication.

Feather Keys

1. Feather Keys, a type are used for shafts from 0.25 inch to 2.5 inches in diameter, and have the same torque capacity as square and rectangular parallel keys.
2. The Feather Key is a square parallel key but with curved ends of fixed radius, and tighter length tolerances.
3. The oval shape of the mating keyshaft slot holds the key in the shaft precisely and tightly, thereby preventing axial movement.
4. Feather Keys are compatible with keyways of all mounted components.
5. These are easily inserted into shafts.
6. This shaft key doesn’t require setscrews to hold them in position.
7. The special square key cannot fall out of the shaft, eliminating any chances of damage to nearby machinery.
8. Feather Keys provide for hassle-free assembly, disassembly and reassembly.

Conclusion

Out of all the mechanical shaft keys, Feather Keys is an outstanding example of a simple yet efficient design that can greatly reduce cost of manufacture and assembly.

Several other such shaft key designs need to be investigated for efficient and cost-effective power transmission.