On 2013-10-31, Jon Elson wrote:
Ignoramus22345 wrote:

I have a particular tool and cutter grinder. Its head is noisy, in
fact, its noise resembles the sound of a rotary siren (though not as
loud). Would you say that the most likely cause of it is bad bearings?
Depends on the construction. If a standard 60 Hz motor with belts,
then definitely has to be bearings. If a universal motor or other
direct-drive high speed motor, then it may actually be designed that
way (although annoying). I have an air bearing PCB drill spindle
that can run up to 80K RPM or so. It has a "spurt" hole when the spindle
lines up with a hole in the housing that lets a burst of air out of
the bearings. It definitely sounds like a siren, and also uses a lot of
air.

Jon

It is a motor plus belt plus spindle.

i