Shaft Alignment Frustrations - 3 Common Reasons

Achieving a perfect alignment can seem daunting at times. Perhaps you have gone through all the recommended pre-alignment steps, taken your measurements correctly, and made the recommended adjustments, and yet you still get an unpredictable result. Sound familiar? If so, you may need to consider these three factors which may be preventing you from attaining accurate and repeatable alignment results.

The first most common reason for unpredictable alignment results is looseness of some kind. This could be looseness in:

• Couplings
• Bolts
• Sensors
• Chain or magnetic brackets
• Motor feet

This is not an exhaustive list but is a good place to start. For a more thorough list of things to check, see a companion  blog article titled “Troubleshooting Looseness during Shaft Alignment.”

The next common reason for unpredictable alignment results is failing to address backlash.

According to a previous  blog post titled “Coupling Backlash—How it Affects Alignment, and How to Minimize it”:

“Simply stated, backlash is angular movement in any mechanical system between mating parts. Coupling backlash is common, and to a point, desirable in many types of couplings. However, the amount of coupling backlash required for efficient coupling backlash is minimal. Often, excessive coupling backlash is caused by a worn coupling insert.”

Causes of backlash can include but are not limited to:

• Worn coupling insert
• Improper hub to shaft fit
• Loose foot bolts

Be sure that you make it a priority to replace machine parts that are suffering from excessive wear in order to prevent backlash issues.

The last issue which is a common cause of alignment frustration and unpredictable results is soft foot.

“Soft foot is a common issue when aligning rotating equipment. It is a major cause of repeatability problems in shaft alignment measurements. In addition to alignment quality and repeatability problems, it can be a cause of machinery vibration, reduce life in electric motors, and cause internal clearance problems in gearboxes and pumps.

But if the proper precautions are taken, soft foot can be minimized and controlled.”

So now you know the top three reasons why you may be getting unpredictable alignment readings despite ostensibly doing everything correctly. We recommend methodically going through these three steps to check for looseness, backlash.