Pre-alignment

The pre-alignment steps of machinery alignment, while fundamental, are critical to performing accurate alignment. Simply put, pre-alignment are the things that should be done before alignment is attempted.

Preparation. In addition to have the proper permissions, safety procedures, and tools in place, preparation for precision alignment should include a brief inspection of the machine to be aligned.

  • Inspect the coupling to see if the insert should be replaced, or if coupling lubrication is sufficient.
  • Check for loose bolting – anywhere on the machine, but especially the feet of the machines to be aligned, keyways, hubs, etc.
  • Check for obvious pipe strain.

Rough-In the Shafts With A Straightedge. This allows the aligner to position the moveable shaft centerline roughly in position with the stationary shaft centerline, both vertically and horizontally. Doing so will save time and increase the accuracy of the laser shaft alignment process. Rough-in should be within 20 mils or so.

Correct Gross Soft Foot. With the hold down bolts of the moveable machine loose, check for gross soft foot. This can be done in a number of ways:

  • Using a 5 mils feeler gauge or shim, check three corners of each foot, to see if the shim will fit underneath the foot. If it does, step up to the next thicker shim until the void under each foot is minimized.
  • Try moving the shims of each foot, either by hand, or by using a small pry bar, to see if the shims move. If they move easily, soft foot remains. Step up to a thicker shim until movement is minimized.
  • Use a dial indicator to measure how much the foot moves vertically. Shim by this amount until movement of the indicator is minimized.

Repeat this process for each foot.

Tighten The Feet In A Diagonal (Criss-Cross) Tightening Pattern. This serves to control any remaining soft foot, minimizing the chances of uncontrolled vertical movement of the machine. It should be done EVERY TIME the feet of the moveable machine are loosened and re-tightened.

Correct Final Soft Foot. Loosening only one foot of the moveable machine, check for any additional remaining soft foot at the loosened foot, using any of the processes discussed above for measuring gross soft foot. Correct as needed, and tighten the hold down bolt back down. Proceed to the next foot, continuing the process until all four feet have been checked.

Using the process outline above will minimize soft foot, get the alignment reasonably close, control any remaining small amounts of soft foot, and increase the repeatability of the laser alignment measurements.

 

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