TOM WALKER wrote to ROY WITT:

 RW>> You could have used a Japanese bearing and had the same quality, but
 RW>> less cost. I used to rebuild IBM hard drives (12" discs) and used a
 RW>> Japanese bearing in place of the original. They were just as good.
 RW>> The bearings that IBM used had to be bought in matched pairs and
 RW>> cost an arm and a leg. I used non-matched bearings and had no
 RW>> complaints.

 TW> Well in some cases "matched bearings" are manditory if one does not
 TW> want a early failure.

These IBM HDs were 512k on 5 or 6, single sided 12" discs...I collected
bad discs and drilled a hole in them and used the very large center hole
as a picture frame.

The hub on which the HD discs rode was extra heavy duty and required the
invention of a special tool to remove the top bearing (which was glued
into place with #609 loctite). I still have that tool, as it was a very
innovative design that I designed and made. This tool saved hours of
disassembly time, which made the rebuilding procedure take 8 hours, just
for one hub. With the tool, we could do 7 to 8 per day.

 TW> I am thinking of my experieces with Gyroscopes used in navigation
 TW> equipment. They of course spun up much higher speeds than the Old
 TW> Hard Drives, Up to 24,000 RPM

I don't recall the speed of the hub, but it rode on 6001 series bearings,
which are  very stable at lower speeds. I think that once assembled, the
hub was originally balanced with the discs mounted. They did the balancing
by drilling a series of holes in it. Not exactly gyroscopic protocol.
Anyway, we never re-checked the balance.


         R\%/itt


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