Shaft alignment procedures

Prior to anv machineiy alignment procedure, it is imperative to check for machine pipe strain. This is accomplished by the placement of dial indicators on the shaft and then loosening the hold-down bolts. Movements of greater than 1 mil are considered indication of a pipe strain condition. 

This method is most usefiil when only one of the shafts can be rotated for the alignment procedure, or when the two shaft ends are very close to each other. Obtain the displacement readings with the dial on the rim (OD) of the coupling and the coupling face. Project these readings mathematically or graphically to the motor base to determine the required adjustments and shims for each foot. This method is not as precise and may have a built-in error, if the coupling center is eccentric from the shaft centerline. 

Two perfectly aligned shafts are colinear and operate as a solid shaft when coupled. This condition is illustrated in Figure 54.1. However, it is extremely rare for two shafts to be perfectly aligned without an alignment procedure... 

Soft-foot is the condition when all four of a machine s feet do not support the weight of the machine. It is important to determine if this condition is present prior to performing shaft alignment on a piece of machinery. Not correcting soft-foot prior to alignment is a major cause of frustration and lost time during the aligning procedure. 

Measurements taken with this device are based on a point of reference at the zero position, which is defined as the alignment fixture at the top of the shaft - referred to as the 12 o clock position. In order to perform the alignment procedure, readings also are required at the 3, 6, and 9 o clock positions. 

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