What is shaft alignment?

Shaft alignment is the aligning of two or more shafts with each other to within a tolerated margin. Proper shaft alignment is dictated by the proper centers of rotation of the shaft supporting members (the machine bearings). It is an absolute requirement for machinery before the machinery is put in service.

Any misalignment between the two shafts increases the stress on each shaft and will almost certainly result in premature breakdown of the equipment or cause excessive damage to your bearings or mechanical seals. This can be very costly to repair and to your production. A proper shaft alignment can prevent this.]

Types of Misalignment

There are two components of misalignment, parallel (also referred to as "offset"") and angular (also referred to as "gap"") misalignment. With parallel misalignment, the centerlines of both shafts are parallel but they are offset. With angular misalignment, the shafts are at an angle to each other.

Parallel misalignment is determined by the distance between the shaft centers of rotation measured at the plane of power transmission. The typical units for this measurement are mils (where 1 mil = 0.001 in. or .025 mm).

In parallel misalignment, there are two checkpoints to look for, horizontal and vertical misalignment. Horizontal misalignment is misalignment of the shafts in the horizontal plane and vertical misalignment is misalignment of the shafts in the vertical plane.

Parallel Horizontal Misalignment: The motor shaft is moved horizontally away from the pump shaft, but both shafts are still in the same horizontal plane and parallel.  Parallel Vertical Misalignment: The motor shaft is moved vertically away from the pump shaft, but both shafts are still in the same vertical plane and parallel.

Angular misalignment is also defined by horizontal and vertical misalignment.

Angular Horizontal Misalignment: The motor shaft is under an angle with the pump shaft but both shafts are still in the same horizontal plane.  Angular Vertical Misalignment: The motor shaft is under an angle with the pump shaft but both shafts are still in the same vertical plane.

Errors of alignment can be caused by parallel misalignment, angular misalignment or a combination of both misalignments.