According to Joseph Gwinn :
In article ,
Eric R Snow wrote:

[ ... ]

Years ago I was blowing out some bearings with air. Goofing off, with
the bearing on my finger, I spun one up and listened to the pitch. As
it spun the pitch got higher until I couldn't hear it. Just as it
passed into my ultrasonic range it exploded with a bang.

Ultrasonic! Wow. That implies a ball-passing frequency exceeding
20,000 per second or so. If the ball cage has ten balls in it, the cage
is rotating at 2000 rps, or 120,000 rpm, and the outer race a factor
faster. No wonder it exploded.

Do you recall the dimensions of the deceased ball bearing?

Since it was on his finger, a guess says that the ID of the
inner race was probably on the order of 5/8". Scale the rest to that.


The bearing
axis was perpendicular to my body so that the bearing parts were
embedded into the wall and not me. My finger hurt like hell. I think
the bearing must have exploded pretty equally because otherwise that
finger would have probably broken instead.

[ ... ]

I don't spin up bearings
any more. Not even a little.

It sounds like there is actually quite a wide safe range here. Just
stay in the sonic range?

That depends on the size of the bearing -- and your personal
hearing range. :-)

A large bearing (say 1-1/2" ID on the inner race) could probably
get to dangerous speeds while the tone remained in the audible range.
And -- it is affected in part by the number of balls in the race. Some
(for heavy loads) have completely full races, others have fewer balls,
with some mechanism to space them out. I've seen ribbons of steel
formed into cups around both sides riveted together. I've seen bakelite
machined to slip in from one side once the bearings are properly spaced.
I've even seen bearings with little coil springs set between the balls
to keep them spaced out. This was in a vary slow, and very low
operating force setup -- like a gimbal gyro cage.

Enjoy,
DoN.
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