Re: [CAD_CAM_EDM_DRO] Re: Cheap 56,000RPM milling upgrade (not a dremel :)

cnc_4_me wrote:

>
>
>>It is a high frequency AC induction motor, but uses air for the
>>
>>
>bearings
>
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>>(both radial
>>and thrust) as well as air cooling of the motor. When you turn on
>>
>>
>the
>
>
>>air, the spindle
>>begins to float, and if you flip it with your fingers, it will spin
>>
>>
>for
>
>
>>minutes.
>>
>>
>
>
>What would happen if you do not turn on the air and then operate the
>motor. Will it run in a derated mode.
>
>

The bearings will burn up. Since this is a $6000 spindle, I sure don't
want to find out.
Actually, I had an air hose blow off while it was running, and it kept
spinning just fine
until that hole was completed, then I shut it off. The thrust bearing
won't work worth
a darn without air, but the radial bearings seem to work well, as their
design makes
them somewhat hydrodynamic.

To be totally clear, these are not air-cooled bearings. The spindle
flies on a cushion
of air, within a bearing that is a VERY close fit to the journal. Air
is injected
from a bunch of radial holes in the bearing. I think the bearing
clearance is in
the region of .0002" per side. So, these bearings crash every time the
air is turned
off.

Jon