Chuck Yung 
EASA Technical Support Specialist 

When vibration problems occur, the magnitude and direction of the vi­bration can give a good indication of where to look for the cause. When vi­bration is higher in the vertical plane, one of the first things we should examine is the base/foundation of the motor. If the high vertical readings are compounded by indications of an eccentric airgap, such as high axial vibration and a predominant twice-line-frequency vibration, a “soft foot” or twisted frame is often to blame. 

Construction basics 
It is common practice for the align­ment technician to use prefabricated shims under the feet, sized to accept the hold-down bolt. The person perform­ing the alignment may not realize that a motor frame is not as solid as it appears. The fact that the foot itself might be over an inch (25 mm) thick, and the frame is cast iron or steel, causes the person to assume that it cannot distort. Nothing could be further from the truth. Because of that assumption, shims are often not placed to the greatest benefit. By understanding some construction basics, we can better place the shims to obtain the lowest vibration readings. 

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Categories: Alignment, Base/soleplate/foundation/mounting, Vibration

Tags: Vibration Alignment Baseplate

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