November 12, 2012
Solving Base-Bound and Bolt-Bound Shaft Alignment Problems
By Brad Case
If you align machinery for a living then more than likely you have encountered machines that are base-bound or bolt-bound.
Base-bound is when the movable machine has to be lowered and there are either too few or no shims under the movable machine feet to accomplish the vertical alignment.
Bolt-bound is when the movable machine is up against the hold down bolts preventing further adjustment in the direction needed to complete the horizontal alignment.
As discussed in a previous alignment blog, the best way to prevent base/bolt-bound conditions is to rough align the machines during installation before piping and other components are connected.
What about machines that have been operating for decades? Case in point, an alignment check of a shredder revealed extreme shaft misalignment in the horizontal plane! Wow! As was feared the movable machine was bolt-bound.
When bolt-bound, typical thoughts are we have to:
- move the stationary machine, hmm that’s a lot to move!
- drill out the movable machine feet, hmm a 1” larger hole? Don’t think so.
- use undercut bolts on the movable machine feet, nope that’s too much material to remove from the bolts.
So, before you undercut bolts, drag out the hoists, drill motor and other equipment needed to correct the bolt-bound condition, consider alternate moves. When either machine is used as the reference, the other machine typically requires a large move as well to correct the alignment. Alternate moves allow the aligner to change the reference to minimize the movement of each machine permitting the shaft alignment to be completed with much less work and less time.
The Foot Lock function in the Fixturlaser XA Pro allows the aligner to easily determine if an alternate move is possible. From the live adjustment screen the Foot Lock icon is pressed. If solving for base-bound, simply rotate the sensors to a vertical plane or leave them in the horizontal plane to solve for bolt-bound. After the dimensions are entered for the stationary machine, open locks appear under the feet of both machines.
Simply press any two locks to close them; the XA will display the corrections necessary to complete the alignment to the new reference. If the adjustment indicated is not acceptable, change the reference by unlocking the locks and closing two different locks.
In the case of this alignment, the best choice with the minimal correction is to lock the outboard feet of each machine.
After the horizontal correction was made and hold down bolts tightened, a new set of measurements were taken followed by a slight vertical and horizontal adjustment. A final measurement was made with the following results.
While not completely in tolerance, a dramatic improvement in the horizontal and vertical alignment was achieved in less than two hours with minimal effort. It was determined a slight soft foot condition, due to rust on the ¼” carbon steel spacer plates under the motor feet, was contributing to the horizontal offset moving when the hold down bolts were tightened. New plates are to be installed and the alignment fine-tuned.