[SLL] Laptop getting a bit warm --> [OT] HD magnets, etc.

[Nicholas Bodley]

On Mon, 23 Jul 2007 14:04:06 -0400, Robert Woodcock <rcw at blarg.net> wrote:

> For fun: find two hard disk magnets that are still attached to each other
> (so there's a slot between them where the hard drive seek head would
> normally go), find an old floppy disk with a metal shield, take some
> scissors and cut a piece of the shield to fit the slot, and drop it  
> through.

Great! Try that with some sheet copper (scrap roof flashing copper is  
good), or (not as good) sheet aluminum. Try to find the thickest that will  
fit, or fold back and forth and flatten the bends to create a thicker  
piece. Believe me, it's worth trying. One term for the phenomenon is  
"magnetic drag", and it's not commonly known. Modern high-flux magnets  
make it a lot easier to demonstrate.

Btw, magnets this powerful, wonderful as they are, can give a nasty pinch;  
when you try to pull free, the "air" gap becomes smaller, and the  
attractive force increases*. Try not to panic, and find something  
non-magnetic to keep them apart. The option is to leave a biological  
specimen behind. *If the new gap is 1/3 as large, the force is 9 times as  
great.

I'd call it the [head[comb]] actuator [drive] coil, btw. "Voice coil"  
refers to loudspeakers, but this geometry is different, and that's not an  
accurate term.

These magnets are a delight; also lovely is the preloaded ball bearing  
assembly for the head comb+actuator pivot. The disc spin motor just has to  
have bearings with extremely- low runout, too. I think of it as the  
headstock for a watchmaker's lathe. Platters might be optically flat.  
(These days, you need a few tiny Torx drivers to open up HDs. Wiha in  
Germany makes some nice ones; they're sold in the USA; Micro Center might  
have them.)

Optical drives have "low-cogging" motors, btw. You don't feel any "bumps"  
when you spin their shafts. They probably start at a fraction of a volt.

Regards,

-- 
Nicholas  B o d l e y
Waltham, Mass.