vibration/alignment/balance

We recently acquired a clients who is interested for using spectral analysis of vibration for mainly the spindles of different machine tools.
Normally those motors (12kw - 0 to 15000rpm) run for about 8500 houres before returning to the supplier for a preventif and complete overhaul.
I would like to hear from your experiences and toughts about measuring these type of machines.
- Wich arguments are especially true for machine tools and what are your recomandations.
- Is your client (or company) willing to expand the, in this case, 8500h life expectance when measurements are good? (this would be an argument to lower maintenance costs, but he would ignore suppliers recommandation)
- Can you measure while making a piece (steel, titanium, alu) or not?
- Was your client able to save much on cuttingtools by lowering the measured vibrationlevel? Was there a clear relation between broken cuttingtool and surface quality with the vib level?
- Did the client noticed a shorter unforeseen downtime?
Thank you.

Looseness of the spindle is standard fault as the preload system is fatigued by using to large tools much more common than classical bearing fault.
Yes operational time is expanded or in worst case shorted (by crash or bad delivery of spindle from start as example) until fault is diagnosed.
In some cases that may result in 10-15 years operation before service.
Here some refurb is done locally in house at the plant, some outsourced to spindle service providers, they are rarely returned to manufacturer unless warranty issues.
Measurement is made when not cutting in repeatable suitable speed selected not to be near resonance or so and also without tool.
Can´t tell about tool cost.
In this case operation was 24x7 all week less 30 minutes Sundays so aim was to detect problems during daytime. Good luck. Olov

OLI had a good answer but I would add:
You cannot check unit while it is cutting. Check must be done unloaded and with the same tool installed and running at the same speed each time. The fact that production has to shut down for a check is usually the hard sell. It will increase the life because the 8500 would be based on a worse cast senario.