What is a Shaft Coupling?

A shaft coupling is used to join two shafts and create a union in an automobile or other engine type. In many instances, the shaft couplings are in place to facilitate removal in the event of needed repair. The shaft coupling may also have been designed to ease installation at the assembly plant. Often it is used to join different sized shafts together or to join a solid shaft with a flexible shaft.

A shaft coupling may be attached by several different methods. Some couplings are welded, while others are bolted or held in place with set screws. Often a shaft coupling is simply held in place by a press fit. Couplings used in critical areas where they are needed to break loose in the case of impact are often held in place with shear pins. These pins are typically made of a softer material which will shear off and allow the shafts to slide out of the way.

The most common place a shear pin equipped shaft coupling is found in an automobile is in the steering column. Many steering columns are designed to break loose in the event of a frontal collision. This helps to prevent injuries to the vehicle's driver from contact with the steering wheel. A machine, such as a saw, employs shear pins in its saw blade shafts. This is to allow the blade to stop turning in the event of hitting a solid object in the wood, such as a nail.

Many shaft coupling joints are splined. This helps to assure that the coupling will not turn or slip on the shaft. Another helpful design is to place the shaft coupling on a shaft, which is "D" shaped. The coupling can be positioned so that its set screws can be tightened against the flat spot, thus preventing slippage.

When performing routine maintenance on any shaft equipped with a coupling, it is imperative to check the fit of the coupling. A loose coupling could indicate a potential break in the shaft and should be replaced immediately. It is also crucial to check the area in the shaft coupling where any set screw or bolt may be. Any cracking to the coupling or missing retaining bolts would constitute replacement of the coupling.

Shaft couplings that are correctly installed and properly maintained can provide trouble-free use. One trick to keep the couplings from sticking and thereby functioning properly is to apply anti-seize compound to the shafts prior to assembly. With care, these shaft couplings can provide safety as well as top-notch performance in many critical areas for years.