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Correcting Base Bound and Bolt Bound Conditions in the Shaft Alignment Process-Part 1

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Correcting Base Bound and Bolt Bound Conditions in the Shaft Alignment Process-Part 1

One of the most frustrating, expensive, and time consuming parts of shaft alignment is dealing with a Base Bound or Bolt Bound (BBBB) condition.  One or both of these conditions are present in a sizeable population of industrial machines.  And while these can be difficult, there are many options that can be used to correct these conditions, allowing the technician to perform a quality shaft alignment.

The definitions for Base Bound and Bolt Bound are:

  • Base Bound – when the movable machine is sitting higher than the stationary machine, and there are either no shims, or an insufficient amount of shims, to lower the movable machine to the required elevation to align both shafts vertically.



Base bound
  • Bolt Bound – when the movable machine cannot be moved horizontally sufficient to align to the stationary machine shaft. This usually occurs due to the hold down bolts of the movable machine contacting the holes of the motor feet, making sufficient horizontal movement impossible for alignment.

Bolt bound


Maintenance personnel use many methods to attempt to correct these problems, such as:

Base Bound

  • Grind or machine material off the motor feet.
  • Machine material off the machine base, using a portable milling machine, or grinder.
  • Cut the machine base with a torch, and re-weld to lower part of the base.
  • Shim up the stationary machine.


Bolt Bound

  • Drill out or slot the holes in the motor feet.
  • Machine the threads off part of the motor hold down bolts.
  • Replace the existing bolts with smaller diameter bolts.
  • Move stationary machine horizontally.


While any of these methods can be employed, some require extensive manpower and down time. They may also make the motor unsuitable for other installations, by changing the NEMA-rated height or bolt-hole diameter of the motor. But there are alternatives that require much less work, are less expensive, and will not cause the machinery to be out of specification.  Stay tuned!

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