An interesting situation arises when the base of the equipment you are aligning is purposely out of level. Which way is up?
This picture shows a setup we used during a recent training class to illustrate the technique (no photos could be taken in the field). Most normal methods of alignment calculate angles assuming the base is level relative to the ground. Our horizontal moves are parallel with the ground and our vertical moves are perpendicular to the ground. When the base is rotated relative to the ground, our frame of reference needs to rotate as well.
The Clock mode on the XA replicates the tried and true reverse dial indicator alignment. The first two readings at 9 o’clock and 3 o’clock define the horizontal move. The third reading at 12 o’clock defines the vertical move. When our frame of reference is rotated, we simply redefine what horizontal and vertical are.
Since the horizontal move is the move parallel with the base, the 9 o’clock and 3 o’clock readings are taken parallel relative to the base. It’s ok that the sensors are not level to the earth. The third reading at 12 o’clock is taken perpendicular to the base. When the results are displayed and it’s time to adjust the machine, we can still do the VertiZontal compound move. The vertical adjustment—the move perpendicular to the base—is made first. After the shims have been added or removed, a little more finesse will be required for the horizontal move. How steeply rotated the piece of equipment is will determine how hard you are working against gravity. Jack bolts will help hold the equipment in place on the base and make this process a lot safer and easier.
When the angle and offset are within tolerance, tighten the bolts (torque it down in multiple passes) and remeasure.