Categories: Shaft Alignment

Coupling Alignment Tolerances vs. Shaft Alignment Tolerances

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By on October 8, 2014

A coupling alignment tolerance and a shaft alignment tolerance are different things – VERY different things!

  • A Coupling Alignment Tolerance is often (but not always) the maximum amount of misalignment the coupling will operate at before premature failure.
  • A Shaft Alignment Tolerance is the maximum amount of misalignment the shafts can tolerate before they begin to transfer radial and axial loads to the bearings, seals, gears, and other affected machine components.

Here are a couple of photos I took of failed coupling inserts. These were taken during some of our training classes. In each instance, I was told that the shafts were aligned to the coupling alignment tolerance. On one, the offset misalignment was about 18 mils. On the other, the angular misalignment was about 3 mils per inch.

photo 1    Photo 2

While the couplings did transfer power for a brief time, the loads from misalignment, along with frequent starts, caused them to fail before their time. It’s not the coupling’s fault. It is a lack of understanding of the differences between coupling misalignment and shaft misalignment. And the coupling, seals, bearings, and productivity pay the price.

In our quest to Realign America we want to start an alignment movement! We need to accept the fact that the allowable misalignment for the coupling, and the allowable misalignment for the shafts, are two different things. And we need to start calling precision alignment “Shaft Alignment”, not “Coupling Alignment”!

Who’s with me?

About the Author

Stan Riddle joined VibrAlign in 2008. He has over 35 years experience in aligning industrial machinery. Stan received his AAS Degree in Machinist Technology from Surry Community College in Dobson, NC, and also holds a diploma in Industrial Systems Technology from Forsyth Technical Community College in Winston-Salem, NC, where he was also an instructor in the program.

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.

4 responses to “Coupling Alignment Tolerances vs. Shaft Alignment Tolerances”

  1. Peter Stromberg says:

    I’m with you!

  2. Andrew Martin says:

    could not agree more!

  3. Jim Westbrook says:

    Stan several of us were in a class that you held in Kensawee,
    Ga. last November. You said that you were writing a book on
    alignment I just wondered if you had completed the book and
    if you have where can I purchase a copy of It.
    Thanks
    Jim

  4. Stan Riddle says:

    Still working on it Jim. But thanks for asking. We do have lots of good information on our blog-www.thealignmentblog.com.