Vibration analysis for CNC machinery.
I am no expert in this field, but here is my opinion from my experience.

I do not often call somone in for vibration analysis unless there are some really flaky things going on. But from my experience I think it is much more useful if it is performed on a consistent basis so you have something to compare it to the next time. It is very hard to tell for one how qualified the professional is that is doing your checks. Second, they will talk a language that is usually over your head. The more you question to try to understand, the more frustrated you can sometimes get. The half a dozen times I or the customer decided to call, a vibration analysis rep in to determine the problem. They could never say yes the motor is bad, the bearings, or the spindle is bad. I ask how confident they are in one thing and it is usually a 60 % chance. Not sure about you but is it worth it to bring someone in and pay them for a 60% chance. The times I have seen it done have been without baselines, so I know this makes it harder to begin with. Basically your looking for change and find out the reason for it before something breaks down. They always ask for the part number of the bearings to determine the number of balls. Which will help determine the harmonics they see. Unfortunately, this is usually not available. I will provide you with some links to other sites that give you a better explanation.

I am interested in hearing what other people have to say on this subject and will gladly post your thoughts on this as well. Or better yet if some of you vibration analysis guys have an article or something to help explain in detail or show graphs on this. I would be more then willing to post them to help other people better understand vibration analysis. I will provide you with some links to other sites that give you a better explanation.