March 18, 2016
Overcome the Frustration of Being Bolt-Bound or Base-Bound
By Tom Shelton
Many blogs have been written about what it means to be either base-bound or bolt-bound and how to correct the situation. I want to write again about it because I encounter this frustration scenario in almost every training class.
I am surprised by how many millwright/mechanics (including myself) can get so wrapped up in the process of precision shaft alignment that we can’t think clearly when something out of the ordinary occurs such as being bolt or base bound. We seem to overlook the easy answers and jump straight the “obvious” answer. The limited movement of the “movable” machines caused by being either base or bolt bound is one these occurrences. The typical “obvious” response is to either turn down bolts, drill out motor feet or start machining the base. We have definitely over looked the “easy” obvious answer.
Bolt-bound means limited horizontal movement, usually caused by the motor feet hitting the hold down bolts. Sometimes the limitation is caused by other components such as rigid conduit connected to the connection box on an electric motor or another piece of equipment resting against a motor.
Base-bound is limited vertical movement, which occurs when the moveable machine is higher than the stationary machine and cannot be lowered due to a lack of shims or too few shims under the motor feet.
The obvious solution to both of these challenges is to move another component. Depending upon the situation, this could mean different things. For instance, moving the junction box as shown in the next photo, or simply turning or raising the stationary machine.
I believe the denotation “stationary” causes a bit of the problem. Stationary is simply a term used to denote one element of the two machines to be aligned as the “Target”. Sometimes you have to move the target to a slightly different position so the “movable” machine can be adjusted to complete the alignment.
Fortunately, some of our tools have a feature called “Feet Lock”. This function allows you to lock any two sets of feet on the machines being aligned and recalculates the required moves to eliminate the “bound” condition. Feet Lock can be used for either the vertical and horizontal planes or both.
Vertical Feet Lock
Horizontal Feet Lock
There are times when the “stationary” machine is truly immovable. For example, when the stationary object is a driven roll in a paper machine that is optically aligned to 40+ additional rolls… that is a stationary object. You cannot just relocate that roll. A pump on the other hand, may have the potential to be moved by loosening the hold down bolts and cracking the pipe flanges. It is quite possible to reposition the “stationary” pump to allow the alignment to be completed as we typically require only a few thousandths of movement to complete the alignment. Drilling, machining or turning down bolts should be the last options!