Normally, it is faster and more accurate to perform shaft alignment while the machines are coupled together. This offers several benefits such as:
However, there are occasions when the coupling might need to be separated as part of the alignment process.
Here are three examples:
If your laser alignment tool has built-in inclinometers, in the sensors, an uncoupled shaft alignment should not be difficult. Use the inclinometer values to set both sensors to the first measurement position, and collect your initial measurement. Rotate one sensor to the second position then rotate the other sensor to the second position, matching the inclinometer values for each and measure. Repeat this process for the third measurement. Make sure to check your inclinometers before each measurement.
A simple method of detecting whether or not the coupling should be removed for the alignment is simply by monitoring the coupling values. After performing the pre-alignment steps, measure the misalignment then shim/move to correct the misalignment as indicated. Re-measure. If the values are not very close to being in tolerance, and if you have carefully taken your measurements, suspect that the coupling stiffness is influencing the shaft’s rotational centerlines. Re-measure for misalignment, this time with the shafts uncoupled, and see if the measurement changes.
Once the machines have been aligned, re-couple the shafts, and re-measure your alignment. Your values should not change more than 1-2 mils.