Okay, so I'm late and catching up, but Gunner
wrote on Wed, 12 Apr 2006 15:18:35 GMT in rec.crafts.metalworking :
On Wed, 12 Apr 2006 07:18:44 -0700, Eric R Snow
wrote:

On Tue, 11 Apr 2006 23:24:21 -0500, Joseph Gwinn
wrote:

In article ,
Eric R Snow wrote:

On Tue, 11 Apr 2006 11:21:34 -0700, "Ken Davey"
wrote:


O.K. As long as you don't spin the bearing with the compressed
air. *That* can be disastrous.

How so?

It can spin up to a fast enough RPM so the centrifugal force (I
know -- there really is no such thing) will cause it to fly apart
-- turning it into shrapnel -- and *you* into a target. I don't
know whether there is any size limit for this to happen, but it
has been known to happen and to harm or kill people nearby.

Ahh. I can see a large bearing being driven fast enough to explode,
especially as bearing races are designed to be reinforced by being
pressed into a recess in a larger housing.

However, One would think that overspeed isn't going to be an issue
with small bearings already specified for 30,000 rpm, unless one's
air supply is something else.


Spinnning a bearing with compressed air is a complete NONO!
Firstly this practice will ruin the bearing - think no lubrication.
Dangerous - as has been mentioned the bearing can explode and sometimes the
bearing will seize.
As the handiest workholder is a finger a seizure at high speed will severely
damage said workholder.

Cleaning with air is quite allright - oil the bearing immediately after such
treatment as moisture will be present in the air and/or will condence on the
(now) cold bearing.

Regards.
Ken

--
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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.
MY ultrasonic range. I know my high frequency hearing is damaged. But
it was still really spinning fast.

Do you recall the dimensions of the deceased ball bearing?
The ID was about 5/8 and the OD maybe 1 1/2, 1/34.


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.

Yes. Lab ultra-centrifuges are built inside a heavy steel box, to
contain the shards of the rotor, when (not if) it explodes. When this
happens, the centrifuge is totally destroyed.


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?
No way. A small bearing may take the rpm. But a larger one will
explode much sooner. Just don't spin 'em up.

Joe Gwinn


Im going to have to try that one of these days.

Safely of course.

After watching the video of the guy spinning up CDs on his Dremel, and
having a few explode on the wheel ... bearings seem to be a logical next
step. Should be simple to whomp up a bearing holder so that you can do
this with your hands in your pockets.
--
pyotr filipivich.
as an explaination for the decline in the US's tech edge, James
Niccol wrote "It used to be that the USA was pretty good at
producing stuff teenaged boys could lose a finger or two playing with."