"DoN. Nichols" wrote in message
...
According to Ned Simmons :
In article , says...

[ ... ]

It could simply be giving a little kick to each ball as it
rotates past -- picking a different part of the sloping trailing edge
of
the balls depending on speed, so the actual speed of the bearings could
exceed the airflow velocity.

I think it much more likely that air bouncing back off the balls and
retainer interferes with the airstream from the nozzle. I'd be surprised
if the balls reached anywhere near the velocity of the air, and I doubt
the airsteam approaches the speed of sound.

Possible -- I have no way to prove any of this -- nor any desire
to explode bearings in the test process. :-)

[ ... ]

Huh, look what a google on - supersonic air flow blowgun - turned
up...
http://yarchive.net/metal/ball_bearing_spinup.html

Interesting, I get a:

================================================== ====================
Not Found

The requested URL /metal/ball_bearing_spinup.htm was not
found on this server.
================================================== ====================

when I try that URL. What is it -- this discussion?


In a strange sense, yes. But 13 years ago on this very group. This is
the thread on google...
http://tinyurl.com/loxlq

O.K. That one worked.

It seems that nothing was settled that time, either. :-)

Thanks,
DoN.

The thing that stands out is the fellow that ran some tests on bearings said
after his testing the bearing was worn out and useless. That pretty well
substantiates my position that even if you don't explode the bearing you are
causing harm to the bearing.
Also supporting your position that spinning it with air is a bad idea if you
want to use the bearing again.
Add to that several examples of the bearings exploding for whatever reason
while spinning them with air and I feel like your point is proven. Granted
I have only heard of used bearings exploding when cleaned and then spun up
with air so it is probable that there were small fractures in the outer race
that allowed it to come apart sooner than all the math would suggest.
It was still cool to watch those suckers fly down the road shooting a
rooster tail of sparks

Glenn
Reformed bearing spinner