Fwd: [ATM] Unusual testing flat

["Matthew L. Brown" <mlbrown@everstrive.com>]

I used to work in the hard drive industry (3 years ago). The disk flatness 
spec isn't all that great, something like 0.0005 inch / inch.  The read 
heads ride on a very stiff air bearing so the disks don't have to be 
extremely flat.  The most common problem was the disk would warp into a 
shape of a potato chip ('crisp' for anglophones).

The magnets are all permanent neodymium-iron-boron, and, yes, they are very 
strong.
The way to get them off a refrigerator is to slide them sideways.

=Matt


>Delivered-To: mlbrown@0
>From: "Jerry B. Hillman" <JBHillman@ev1.net>
>To: <atm@atmlist.net>
>Date: Mon, 26 Apr 2004 20:05:57 -0500
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>Subject: [ATM] Unusual testing flat
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>Hi all,
>I found something that I believe is the flatest thing I own. It also has a
>mirror bright first surface coating.  If it was larger I would attempt to
>make a secondary out of it.
>What I am refering to is the disk from a computer hard drive.  I have
>several of these that the drives quit working on so I disassembled them for
>the incredible magnets used in them. These are curved magnets about 1/2"
>wide and about 1 1/2" long.  I haven't tested their weight lifting
>capability, but I almost have to use a screwdriver to pry them off my
>refrigerator. Anyway, I saved the disks because they looked useful.  I also
>can see the fringe lines when I put my secondary face down on one of them.
>Now if I only knew for sure if I was testing this flat right. I probably am
>not, but I have read the procedure in both books I own and can't get it to
>work.
>Clear skies, Jerry
>
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