If non-repeatability is an issue and it is not due to the setup of the laser or ambient vibration, then it may be of interest to check the bearing clearances. This can be accomplished very easily with a laser. A little bit of information is necessary to accomplish this. We will need the following:
a) Acceptable bearing clearance and tolerances.
b) Distance between bearings.
c) Distance from the receiver of the laser system to the first bearing.
d) Rotalign® Ultra laser system.
For instance, suppose that the distance between bearings is 10 inches, the distance from the receiver to the first bearing is 5 inches, and the acceptable clearance is 4 mils. This means that with the shaft bottomed out in the bearing, there is a total of 4 mils of clearance available, or lift. With the receiver at the 12:00 o’clock position in XY-View, press the SET ZERO button. This will give you a zero reference for the values displayed on the sensor. Simply lift the shaft until it contacts the top of the bearing and record the Y value of the movement. With the above distances, we are allowed 4 mils/10 inches, (or 0.4 mils/1 inch), 10 inches being the distance between the bearings. From the receiver to the front bearing is 5 inches, so with a good bearing, we would expect to see another 2 mils/5 inches, (or 0.4 mils/ 1 inch). Add the two together and we get a total of 6 mils/15 inches. This means that if the lift of the shaft shows 6 mils of change at the receiver, the clearance is acceptable. If greater than 6 mils, clearances may be excessive.
Alignment, Maintenance Tips by Ana Maria Delgado, CRL