This is probably one of the most common questions we are asked during our alignment training classes. And the best answer might be, “Sometimes, if you must, maybe!” Let me preach on it.
Undercutting bolts is a method used to align machines that are bolt bound. A bolt bound condition occurs when the movable machine cannot be moved horizontally to a degree sufficient to align it to the stationary machine. This most often occurs due to inadequately aligning the machines before other items, such as piping, are installed. Undercutting the bolt reduces its shank diameter, allowing a little more room in the motor foot hole for alignment.
The best method to prevent a bolt bound condition is to rough align the machines before they are installed. Slide both machines as far to one side as they will go and mark the base of the foot. Then slide the machines as far in the other direction as they will go and mark that side. Position both machines in the middle of the two marks and align. This gives you the maximum amount of “hole” in both the driver and driven machines.
On machines already in place, this may not be possible. If you must use undercut bolts, please consult your engineering department guidelines. We offer these guidelines as an opinion only:
While undercutting a bolt may make the alignment easier, it may cause more problems than it corrects. Make every effort to align your equipment with bolts sized by the designer.
What is your site’s policy on undercutting bolts? How are you solving bolt bound issues?