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Understanding Soft Foot and How to Correct It

Ensure Your Precision Alignment Program Is On The Right Foot.

Imagine (or maybe you don’t have to) that you take out your brand new Easy-Laser system, and proceed to perform a shaft alignment.  However, it seems that no matter what you do, you can’t get a great alignment.  What is going on?  The foundation looks good, new shims were used, the asset is clean, and there is no pipe strain.  After some discussion with others, they mention a term in which you are unfamiliar with, soft foot.

Soft foot… this term has come up before.  You know it has something to do with alignment, but don’t quite understand what it is, how it can impact the alignment process or how to measure and correct it.  But you should know more about it, so here is a start

So What is Soft Foot?

Soft foot occurs when all supporting members of the asset do not equally support the asset. In a soft foot condition, the asset does not sit firmly on all supports.  There are two primary types of soft foot that are encountered; Ordinary soft foot and Angular soft foot.

  • Ordinary soft foot is the amount of even gap between one foot of the asset and the base plate.
  • Angular soft foot is the angular or irregular uneven gap between an asset support and the base plate.

What Causes Soft foot?

A variety of issues can cause soft foot.  While not all encompassing, the following could be potential causes of soft foot;

  • Poorly machined supports
  • Dirt or paint under the asset or on the supports
  • Anchor bolts incorrectly torqued during grouting
  • Poor base plate design
  • Poor leveling
  • Grout deterioration and settling
  • Corrosion of the base or foot of the asset
  • External stress on the equipment, such as pipe strain
  • Excess amount of shims (more than 3) which can create a spring effect
  • Bent or damaged machine supports

By being able to recognize some of the potential sources of soft foot, you can actively work to eliminate them before performing alignment work.

Impact of Soft foot

Soft foot can cause many issues, not just making the alignment difficult.  Soft foot is often a major cause of the misalignment. Soft foot can also cause the following;

  • Stress to the machine housing
  • Distort the bearing bores to oval
  • Coupling misalignment/strain
  • Internal misalignment of bearings
  • Increased radial load on bearings
  • Distorted seals
  • Bent Shafts

As you can see, not only does soft foot cause major issues when trying to perform a precision alignment, it can cause long term reliability issues with your assets.   A little more time spent up front addressing soft foot can not only make alignment easier but improve long term reliability.

How to Correct Softfoot

Correcting soft foot is not the easiest of tasks, however, there some actions that can be taken (aside from eliminating the causes above) to eliminate soft foot. These items should be checked and remedied;

  • Confirm that base plates and foundations are installed and leveled to specifications.
  • Make sure that base plates and machine supports are clean and free from dents.
  • Use only clean, flat shims.
  • Once the machine components are placed on the base plate, rough align and perform a gross soft foot check of both the movable and stationary machines using the soft foot tool in your Easy-Laser systems
  • Begin to correct the soft foot, using the recommendations from the soft foot tool to correct ordinary soft foot. If angular soft foot exists, cut one shim in half, leaving the tab in place, to make it easier to reposition.
  • Once the soft foot has been corrected, tighten each bolt, using a crisscross pattern.  Now you are ready to perform the alignment of the equipment

How many of you take the time to look for and address soft foot issues when performing equipment alignment?  Do you have the knowledge to confidently identify and correct soft foot?  If you are looking for assistance in developing a robust alignment program through expert training, or are looking for quality laser alignment equipment such as the award winning Easy Laser XT440, please contact info@hpreliability, or visit our store.

Remember, to find success; you must first solve the problem, then achieve the implementation of the solution, and finally sustain winning results.

I’m James Kovacevic
HP RELIABILITY Inc
Solve, Achieve, Sustain
Follow @HPReliability

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By | 2017-09-02T12:47:33+00:00 September 4th, 2017|Alignment, Early Equipment Management, Equipment Installation|1 Comment

One Comment

  1. Taha Bin Mahmood September 4, 2017 at 10:56 am - Reply

    James, one thing I want to add is how to diagnose soft foot. To confirm soft foot, we use dial indicators or laser alignment tool if available and untighten and retighten each bolt, of any is raise by more than 0.05mm, soft foot is confirmed and should be corrected

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