Shaft alignment - A training Pdf

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What is meant by shaft alignment?

Shaft alignment is the process whereby two or more machines (typically a motor and pump) are positioned such that at the point of power transfer from one shaft to another, the axes of rotation of both shafts should be colinear when the machine is running under normal conditions. 

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Colinear means two lines that are positioned as if they were one line. Colinear as used in alignment means two or more centerlines of rotation with no offset or angularity between them.As with all standard definitions there are exceptions. Some coupling types, for example gear couplings or cardan shafts, require a defined misalignment to ensure correct lubrication when operating.

In the above definition, “at the point of power transfer” refers to the fact that shafts have some form of catenary due to their own weight, and are strictly speaking not straight. Therefore the location where the alignment of the two shafts can be compared is only at the point of power transfer from one shaft to the next.

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The term “axes of rotation” should not lead to confusing “shaft alignment” with “coupling alignment”. The coupling surfaces should not be used to measure alignment condition since they do not represent the rotation axis of the shafts. To save manufacturing costs coupling surfaces are often only rough machined or in some cases not machined at all.

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