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What Is a Shaft Alignment?

B. Turner
B. Turner

A shaft is a cylindrical piece of steel that transfers rotational force from a motor to other components within a piece of machinery or equipment. In order for this transfer of force to take place at the maximum level of efficiency, the shaft that extends from the motor must be properly aligned with those nearby. Each equipment manufacturer provides very specific shaft alignment tolerances that should be met for the machine to function properly. Operators and maintenance personnel within a manufacturing facility often adjust the alignment of these shafts as part of routine maintenance routines. Improper shaft alignment puts unnecessary strain on the motor and other components, which can shorten the life of the machine and increase repairs and downtime.

In order to understand how shaft alignment works, it is helpful to identify the two basic types of alignment. In an angular alignment, technicians make sure that the two shafts share the same slope, and that one is not angled differently than the other. In an offset alignment, technicians determine whether the two shafts sit on the same plane. When shafts feature an offset misalignment, they share the same slope and remain parallel, but do not align end to end. Some machines may even feature a combination of both of these issues, leading to serious problems with performance and efficiency.

Man with a drill
Man with a drill

Each of the two types of shaft alignment issues can occur in either a horizontal or vertical plane. For example, one shaft can sit parallel to the other, yet slightly above it, which demonstrates a vertical offset misalignment. If the two shafts are parallel to one another and to the ground, but do not align end to end, this is known as a horizontal misalignment.

Problems with shaft alignment do not always cause a machine to malfunction. Instead, this misalignment leads to excess noise and vibration. It can also lead to heat and vibration within the motor, which will eventually lead to failure. The vibration can also cause couplings and other connections to fail, leaving the machine inoperable until these connections can be replaced.

Traditionally, technicians started the shaft alignment process by focusing on the vertical alignment, then moving on to the horizontal plane. Today, most maintenance personnel rely on compound alignment techniques, which allow them to adjust shafts along both planes at the same time. This is accomplished by placing a series of sensors along the shafts, then using lasers to determine the correct alignment. Couplings and other connectors are loosened and the shafts are repositioned until the lasers show that the shafts are once again within the specified alignment tolerances.

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