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Soft foot can severely affect the operating condition of a machine, which will undoubtedly shorten its life expectancy. Here are a few simple tips to help avoid soft foot in your machines:

  1. Eliminate rust, dirt and any other contamination from the contact surfaces of the machine feet, shims and frame or foundation.
  2. Never insert more than four shims at a time beneath a single machine foot. More than three shims may cause a spring effect.
  3. Eliminate external forces on the machine such as those from connected piping, conduit, auxiliary supports, etc.
  4. Use high quality, clean and uniform shims when shimming is necessary.

Watch our Shaft Alignment Know-How video on Soft Foot

by Pedro Casanova CRL

By Deron Jozokos with Shoreline Reliability,  LUDECA solutions provider for New England and Eastern New York
Yesterday I visited a customer at a ski resort for an alignment demo and he asked if I would demo our tools on his actual machinery, a recently rebuilt pump that was installed by a vendor. I readily agreed as I thought this would be a good opportunity to show how easy the tool is to use on his actual machinery. After setting up on the pump and motor, we entered the machine dimensions into the SHAFTALIGN computer and took an initial alignment reading and soft foot reading and saved the file “As Found”. In addition to a severe soft foot condition and misalignment, I pointed out some other issues with the machines. The shims used previously were undersized for the motor feet, and the washers used under the hold-down bolts were damaged and “cupped”. Also, on two feet the bolt holes didn’t line up with the foundation bolt holes which resulted in the hold-down bolts being cocked.
I recommended that we fix each issue, all of which could be done fairly quickly. We replaced all of the shims with new precut stainless steel shims, eliminated the soft foot and slid the lower frame laterally so we could line up the bolt holes correctly. From there we re-measured the alignment condition and made the corrections indicated by the SHAFTALIGN system.
Rebuilt Pump Misalignment
We took one last verification measurement and got two Smiley Faces which indicated that the alignment was now within the Excellent range for 1775 RPM tolerances. They were also interested in seeing the new TABALIGN system in action so we downloaded the TABALIGN from the Google Play Store to their Android tablet, synced it to the same sensors and took the measurements which repeated exactly the SHAFTALIGN results. They were very happy with the results but at the same time worried about the rest of their machinery that probably has many of the same issues that we had found on this pump-motor set. They’ll be correcting all of those shortly though!
 

by Ana Maria Delgado, CRL

While visiting a customer’s facility,  I was asked if I could provide some tips on how shims should be replaced when making a required vertical correction on a machine being aligned.
The following steps were recommended to minimize the potential for creating a soft foot:

  • When possible, upon starting the alignment, replace any old, dirty or bent shims with new precut stainless steel shims.
  • Use no more than a combination of three shims to achieve the desired thickness.
  • Always take the time to measure the thickness of any shims thicker than 25 thousandths with a micrometer or Vernier caliper. Shim thicknesses of 50 thousands of an inch or higher may not always be true. The shim thickness may vary by several thousands of an inch. If this is not compensated for, it will create a soft foot problem or result in a failure to meet alignment tolerances.

Shim Thickness

  • If you are not familiar with the soft foot correction procedures, it is a good practice to use a laser shaft alignment system that measures and can also diagnose a soft foot problem.

Download Best Practices: Machinery Alignment Shimming
 

by Mario Rostran CRL

Design,  installation and startup are the biggest contributors to a reliable or unreliable plant.  It is difficult or impossible for a Maintenance Department to overcome issues inserted during one of these stages. Unfortunately,  most often the focus is placed on fixing the equipment after some functional failure has occurred.  The focus should be placed on preventing equipment failures in the first place.
Design and installation consideration should be given to minimizing piping strain.  Piping strain is affected by temperature, flexibility, mounting arrangement and design.  Distortions in machinery from piping strain can lead to increased vibration levels, bearing failures, seal failures, coupling issues and more.
The baseplate should be flat and level.  A warped baseplate can lead to soft foot conditions and difficulty in performing proper equipment alignment and reliability issues.
Soft foot conditions distort the frame of the machine and lead to bearing, seal and electrical issues in equipment.  Additionally, soft foot conditions can make the normal alignment process much more difficult.
Correct placement and adequate adjustment mechanisms for the equipment are required for proper alignment.  The design and installation must allow for any movement required to bring the equipment into proper alignment once it has been placed into position.
Good alignment of the machines also means accounting for any anticipated positional changes in the machines that occur due to thermal growth or operational loading. Compensate for this by aligning equipment to the proper targets in the “cold” condition.
The above items are a few of the things that should be taken into consideration during the design, installation and startup processes.  Failure to do so will lead to difficulty in achieving proper equipment alignment.  Improper alignment leads to functional failures in equipment and reliability problems. Don’t overlook the reliability improvements that are available to you by doing good equipment shaft alignment.

by Trent Phillips

Soft foot conditions lead to a distortion of the equipment’s frame.  Soft foot can exist in several forms such as parallel air gap,  bent foot, squishy foot or an induced soft foot condition.  A good laser alignment tool, adequate training and best practices will help you identify the existence and type of soft foot. This determination is critical, because the proper correction method must be applied.
The resulting frame distortion can lead to several equipment reliability issues.  Some examples are:

  • Coupling misalignment
  • Coupling Strain
  • Internal misalignment of bearings
  • Increased radial load on bearings
  • Distorted bearings
  • Distorted seals
  • Bent Shafts

Watch our Video Course: Soft Foot Checks and Corrections

by Trent Phillips

A lot of maintenance employees believe that small machine trains can be precision aligned more quickly and easily than larger machine trains. This is not always the case!  Smaller machine trains are usually less rigid. This can cause the alignment to shift as the anchor bolts are tightened.  Almost all small machine trains have some form of soft foot condition that must be corrected because the machine bases are often not flat or of inferior construction. Additionally, thermal growth can have a large impact on smaller machine trains as well.
Don’t be fooled by the size of the equipment you must precision align. It is critical to understand how the size, design, operation and other factors affect the equipment you must align.

by Trent Phillips

Soft Foot has often been noted as the most inexact science portion of Shaft Alignment. Historically, when people think of Soft Foot, they often want to neglect, ignore, or otherwise do everything possible to not deal with it. This is one of the traps that leads down the path of bad habits, bad alignments, and more problems down the line.
Shaft alignment can be thought of as two things: 1) Aligning the couplings and 2) Checking for and correcting Soft Foot. Soft Foot, in fact, plays so much of a role in shaft alignment, that if one were to analyze the 6-Step Alignment Procedure below, one can see that Soft Foot actually appears in 3 out of the 6 steps. Therefore, Soft Foot can be thought of as half the alignment job.
Overall Alignment Procedure
1. Pre-alignment checks
2. Rough alignment to “eyeball clean” (with bolts loose).
3. Rough soft foot: Loosen all bolts and “fill any obvious gaps”.
4. Initial alignment. Get to within 5 to 15 mils at coupling or less than 20 mils at feet.
5. Final soft foot. All feet less than 2.0
6. Final alignment within tolerances.
Note: Step # 1 includes shim inspection and cleaning of machine supports
What is Soft Foot?
Soft Foot is Machine Frame Distortion.
How does it happen?
Soft Foot can happen from a number of things, including:
• Bent Feet
• Bad Bases (warped, uneven, flimsy)
• Dirt, rust, corrosion under feet
• Excessive number of shims
• And many more…
What should be done about it?
A full and extensive diagnosis should be done on every machine foot to determine whether or not the tightening of that particular bolt is causing machine frame distortion, and thereby adding coupling misalignment or machine frame strain.  A few helpful tips to remember are:
• Minimize total number of shims under each machine foot to no more than 4 shims per foot.
• Make sure the area is clean, including machine feet, bases, shim packs, etc.
• Any jacking bolts that may be causing force against the machine frame should be backed off, so as to not interfere with the soft foot check.
• When checking for soft foot, only one machine foot should be loosened at a time, and the deflection or movement at the shaft noted.
With advancements in technology, PRUEFTECHNIK laser alignment tools can help diagnose whether a machine has a soft foot. The newest addition to the PRUEFTECHNIK line of tools, the Rotalign ULTRA, not only diagnoses the soft foot condition of the entire machine, but tells the user exactly how much to shim each foot, in order to correct the soft foot condition.
So the next time someone tries to pass off a bad Soft Foot problem as not being “that bad”, be aware that it is 50% of the alignment.  Your machine’s Soft Foot condition should be taken care of, because if it has not, neither has your Shaft Alignment.

by Ana Maria Delgado, CRL

Pipe Strain is Soft Foot!

Yes, pipe strain is soft foot! Soft foot means machine frame distortion. If you are missing shims under a foot and tighten the hold-down bolt until you have forced the foot down to the base, you will have distorted the machine frame. If you have severe pipe stress on a pump, and the anchor bolts are tight, chances are great you are also distorting the pump casing. Consider that if the pump’s anchor bolts were completely loosened or removed, the pump might be hanging in the air from the piping. So if you were now to tighten the anchor bolts, you would be forcing the pump down to the base and distorting it, just as happens when you are missing shims under a foot.
Shimming the feet will rarely solve the problem completely; rather, the correct solution is to eliminate the undesirable pipe stress. “Stress” is the force acting on something, while “strain” is the deflection or distortion resulting from the stress. A soft foot condition means you have machine frame strain, and pipe stress is just one of several examples of this. When the machine casing is distorted, the internal alignment between the bearings is changed and the shaft is deflected. This produces enormous stress on the bearings and increased vibration in your machines, resulting in premature wear and tear as well as loss of efficiency. Your seals and bearings will fail much faster. If a significant soft foot condition exists, a good alignment of the centerlines of the shaft rotation is almost pointless. The machines will still fail more quickly and lose efficiency. How do we diagnose and fix this?
The trick lies in knowing how to recognize that a pipe strain problem exists. The behavior of a machine with pipe strain differs significantly from one whose soft foot condition is caused by one of the more traditional shimming problems or unevenness of base or feet. Fortunately, there is an easy measurement solution: The Pipe Strain Wizard in the OPTALIGN SMART. The Pipe Strain Wizard will guide you through the all of the necessary steps to quickly and easily ascertain whether a pipe strain problem exists and measure its precise impact on the shaft alignment.
Essentially the process involves taking an initial reference reading of the shaft alignment condition. Thereafter the piping is completely loosened and a second reference reading is taken. The wizard then calculates the difference and yields the results.
These results can be documented in a full color Pipe Strain report printed directly from the OPTALIGN SMART to a USB memory stick as a PDF file.
Optalign Smart Pipe Strain Wizard and Report
Any impact on the alignment of more than about 2 mils indicates a pipe strain problem that should be dealt with. Correcting pipe strain is a task for an experienced pipefitter who must see to it that connecting and torquing the piping should not move the machine from its rough aligned condition, nor distort its casing in any way. Proper pipe hanging techniques and a good knowledge of calculating and designing “Dutchman” spacers is essential.

by Alan Luedeking CRL CMRP

The following tips are presented for consideration for when “the going gets tough”, meaning that problems like residual soft foot or “bad geometry” or becoming bolt-bound impede your ability to easily obtain an excellent alignment. First, a few definitions:

  • Residual Soft Foot present: A bit more soft foot than you are comfortable with, but that you can’t do anything about, perhaps from slightly angled feet or a bit of pipe strain. Learn about our Rotalign ULTRA Soft Foot Wizard.
  • Bad geometry: Equipment whose distance from – coupling center to front foot- is equal to or greater than the distance from front foot to back foot.
  • Becoming bolt-bound or base-bound: You must still move a little but have run out of room in the anchor bolt holes in the feet, or must still come down a bit but have no shims left under the feet to remove. Learn about our Rotalign ULTRA Move Simulator.

Final Vertical Misalignment Correction (Horizontal Misalignment already “close”)
1. Get front feet position close to offset tolerance. Finish the alignment by correcting the rear feet only.
2. Final feet position should make offset at the coupling center decrease. To achieve this:
Front feet position 
Positive 
Negative 
Examples: 

-2
Back feet position
More Positive
More Negative
Examples: 
4
-3 etc.
3. It is bad to leave feet positions with opposite signs, even if the values are very small.
Examples:
Front feet position


-2 
Back feet position
-1
-2
1 etc.
4. It is bad to leave the value of the front feet position higher than the backfeet position even if they have the same sign.
  
Examples:
Front feet position

-2 
Back feet position
1
-1 etc.
Final Horizontal Misalignment Correction (After vertical is within tolerance)
The above rules apply for the Horizontal corrections also.  For small equipment remember to torque in steps.

by Pedro Casanova CRL

“Does misalignment waste energy?” is a question often asked. The answer, emphatically, is yes! General Motors Corporation and Ludeca Inc. performed and published a study on this issue in 1993 which showed conclusively that energy savings (Real Power savings) of 2.3 percent could be obtained on loaded machines. On unloaded machines, the savings ranged as high as 9 percent! At ICI Chemicals, a UK chemical plant in the north of England, a carefully controlled doctoral research project revealed even higher savings. Other studies suggest averaged savings of 4 to 5 percent.
In late 1993, Infraspection Institute in New Jersey demonstrated in a carefully controlled study conducted at Miller Brewing Company that misalignment generates heat and wastes energy. This was clearly demonstrated in the comparative infrared signatures obtained on the same machines when running in an aligned and misaligned condition with deferent types of couplings (see Figures 1 and 2.) Precise magnitudes of misalignment were very carefully set with an OPTALIGN® laser system and the results meticulously examined with calibrated thermograms recorded for each case.
Clearly, the energy required to accommodate the increased sliding velocities from misalignment within flexible couplings must come from somewhere, and this wasted energy comes at the direct expense of the efficiency of the rotating machines. While the percentage of savings may not seem very significant, a a plant that reduces energy consumption by 4 percent on an energy bill of $50,000 per month would save $24,000 in just the first year, more than enough to justify the purchase of a higher-end laser shaft alignment system.
Read entire Shaft Alignment, Soft Foot and Energy Savings 

by Alan Luedeking CRL CMRP