The Alignment Triangle

No, it is not the place where good shaft alignments get lost – never to be seen again!  It is a way of thinking about locating machinery feet so that the shafts are in alignment, even when the feet of the moveable machine may be a few thousandths up, down, left, or right of perfect.  Shaft alignment is about aligning the shafts, not the feet.

Think of the shafts as two straight lines – one stationary, representing the stationary machine, and one moveable, representing the moveable machine.

Examine the three graphs below:

In the top graph, the moveable rear feet are 10 mils low, and the moveable front feet are 5 mils high, but the result at the coupling is 8 mils high.

In the middle graph, the moveable rear feet are 5 mils low, and the moveable front feet are 10 mils low, but the result at the coupling is 12 mils low.

In the bottom graph, the moveable rear feet are 10 mils high, and the moveable front feet are 5 mils high.  The result at the coupling is 3 mils high.

Alignment Triangle

Simply put, the “triangle” formed by connecting the foot positions to the reference line should point toward the coupling, not away from it.  Remember this simple rule of thumb;

  • The value of the moveable rear feet (outboard) should be bigger.
  • The value of the moveable front feet (inboard) should be smaller.
  • They should both be the same sign.  In other words, if one is a positive value, both should be a positive value. If one is a negative value, both should be a negative value.

For a better explanation, please read the article Don’t Look at Your Feet by VibrAlign’s founder and CEO, David Zdrojewski.  Click on the link below.

http://www.mt-online.com/component/content/article/66-april/510-dont-look-at-your-feet.html?directory=90

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About the Author

Stan Riddle

Stan Riddle joined VibrAlign in 2008. He has 30 years experience in aligning industrial machinery. Stan began his maintenance career working as a machinist and millwright for companies such as Weyerhaeuser, R.J. Reynolds, and Tyco Electronics. He also has over 25 years experience in Predictive Technologies, such as vibration analysis, thermography, oil analysis, and ultrasonic inspection.


He is a certified Level III Vibration Analyst with the Vibration Institute, and is a Past Chairman and Board Member of the Piedmont Chapter.


Stan and his wife live in Yadkinville, NC where he enjoys wood carving, fishing, and anything else outdoors.


2 Comments
  1. Mac

    Well put Stan.

  2. Mike

    I try to look at it as splitting the difference.

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