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Achieving proper alignment by detecting and correcting soft foot

Publication date: 
May 2016
Gene Vogel, EASA Pump & Vibration Specialist
Type of media: 

Proper alignment of direct-coupled machinery is an essential element in reliability of a new or repaired machine (motor, pump, gear case, etc.). One common impediment to achieving proper alignment and smooth operation is a “soft foot” condition. 

A soft foot occurs when all the feet of a machine case do not sit flat on the supporting base so that tightening the foot bolts causes distortion of the machine case. The source of the soft foot could be a baseplate which is not flat or machine feet which are distorted. Not only does this make it difficult to align the machine, but the casing distortion may add additional load to the bearings and create internal misalignment between the rotating and stationary elements of the machine resulting in poor performance and increased vibration.

This article looks at:

  • Detecting soft foot
  • Correcting soft foot
  • General recommendations for shims
AC motors
DC motors
Repair procedures and tips