Blog

April 6, 2017

Is there such a thing as “Too Good” of a Precision Shaft Alignment?

By Tom Shelton

This question comes up frequently in our Shaft Alignment Best Practices training classes. The result screens below both show two different aligned machines meeting 3600 tolerances.

 

The question is; is one better than the other? There has been a lot of discussion about this very topic. The theories are abundant and points of view innumerable. In measurable terms, I would say that there is virtually no difference.

Once an alignment is within the tolerance range (based on RPM) the difference of the effective wear on these two machines would be minimal if even detectable.

My thought is that, due to normal wear in the machines that we maintain daily, there is in fact a detrimental effect to having a “perfect” alignment. Normal wear increases bearing clearances allowing the rolling elements too much room to “move around” to the detriment of the bearing. The result is axial and radial “float” of the moving elements of the machine.

The results showing the minor misalignment, that are still well within tolerance, could be considered to be slightly preloading the bearings. Preload on a bearing keeps “float” to minimum helping the rolling elements of the bearing to run true in the races.

I think that in a perfect world where machines and all variables are perfect to the design specifications, an engineer would argue the opposite of my theory. My question to that engineer, “Have you ever been in a 50 year old factory and seen anything that remotely resembles perfect?”

If given a choice, I would allow slight misalignment, within tolerance. I like the alignment on the left.

Save Time. Save Money. Save the Machine.