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We previously discussed the Types of Misalignment as a cause of machine failures. In this blog, we will discuss Types of Soft Foot and their impact on machines.

Soft foot means machine frame distortion that occurs when the machine hold down bolts are loosened or tightened. A soft foot condition can lead to internal misalignment of the machine which will add unwanted loads and forces to the bearings. Soft foot will also deflect the shaft as it accommodates for the internal misalignment of the frame of the machine. There are four main types of soft foot:

  • Parallel soft foot: Occurs when one of the feet on the machine does not touch the base while the other three do. This creates a parallel gap between the foot and the base when that foot is loosened.
  • Bent soft foot: Occurs when a foot of the machine is deflected or in an angle with regard to the base. However, this also applies to when the base is in an angle with respect to the foot.
  • Squishy soft foot: Occurs when too many shims are used under the foot. Shims create an accordion effect causing the foot to lift off the ground even when there is no soft foot.
  • Induced soft foot: Occurs when external forces such as piping or electrical conduit pull or push on the machine creating a distortion of the frame.

Soft foot needs be checked and corrected to within 2.0 thousands of an inch to allow the machine’s frame to run free from distortion.

Watch our Shaft Alignment Know-How video to learn about the effects and importance of measuring and correcting Soft Foot when performing shaft alignment.

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by Carlos Bienes CRL