Categories: Shaft Alignment

Axial Alignment?

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By on March 8, 2012

We are sometimes asked, “Does your laser alignment equipment measure axial alignment?” While it sometimes raises some eyebrows, the answer most frequently given is, “There’s no such thing.” What is sometimes referred to by maintenance personnel as “axial alignment” is really axial spacing, or coupling gap.

colinear shaftsShaft alignment refers to orienting two shafts, connected by a coupling, to where they are collinear, or in the same line in space. The reason the term axial alignment is used is because many mechanics learned to correct angular misalignment by measuring the faces of the two coupling flanges. But what is actually measured during the shaft alignment process is angular misalignment, not the coupling gap. They are different.

Coupling gap refers to the distance between the two coupling flanges, and is normally done to allow the coupling to compensate for slight misalignment, to allow the coupling insert to “float,” or have some degree of freedom of movement, to minimize coupling binding, and to prevent unwanted axial or thrust loading of the shaft bearings.

coupling gapThe amount of coupling gap is greatly dependent on the type of coupling used, but it is usually set to a much wider tolerance than is used for shaft alignment.

If your couplings can be moved on the shafts, it is preferable to complete the shaft alignment, and then set the coupling gap. If the coupling flanges are interference fit, sometimes spacer blocks are employed to keep the coupling flanges at the proper spacing.

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.

3 responses to “Axial Alignment?”

  1. I was just doing a little research on Thomas couplings and sure enough, they call the axial spacing axial alignment. I thought about this post as soon as I read it!

  2. Silvio Balieiro says:

    Very good.

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