According to Joseph Gwinn :
In article ,
(DoN. Nichols) wrote:

According to Joseph Gwinn :

[ ... ]

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.

[ ... ]

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.

Yes. I'm tempted to figure out the rough limit. I would guess that it
will be a ratio on the max allowed rpm in service.

Right away we know that the service speed is safe for all but bearings
sold as designed to work only while pressed into a recess. So, if a
bearing is rated to 12,000 rpm, the balls travel at half that, or 6,000
rpm, and there are 10 balls (just count them), then the max tone
frequency is (6000/60)*10= 1,000 Hz.

That said, I don't have perfect pitch (few do), so I would keep it far
lower, a few hundred Hertz - a low hum, rather than a whine or a clear
tone.

That *might* work. I still would not place myself (or anything
that I cared about) in the plane of the rotation.

[ ... ]

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.

I've seen all these variants except the one with the little springs.
What are the springs made of?

I don't know for sure. I've seen them in equipment from the
mid to late 1950s at a guess, and did not test them to destruction.

I don't know that I would be tempted to spin such a bearing at all - the
little springs would get pulled under the balls, and the whole affair
would jam up, or the balls would end up all to one side, allowing the
bearing to disassemble itself long before the outer race could explode.

the springs were coil springs, about 2/3 the diameter of the
balls, so the balls would hold the springs fairly well centered at low
speeds. As I said -- it was run only at very slow speeds. The bearings
in the actual gyroscope (powered by three phase 400 Hz, FWIW) were
fitted with some red/orange synthetic separator -- phenolic, at a guess.

Enjoy,
DoN.

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