Hard Drive Teardown

Here’s something I think all beginning engineering students ought to do: take something apart that has a well established, optimized design and learn from it. And something more involved than a flashlight, like we did for our CAD class. You can’t really glean anything from a flashlight. A mechanical hard disk drive, on the other hand, is a relatively ubiquitous piece of low-tolerance engineering that I thought would be cool to dismantle. I had a dead one lying around and figured I’d crack it open, and maybe salvage the platters for something ornamental.

The layout of a hard drive is pretty simple, you have a cast aluminum body that holds everything together, and a controller/interface card on the bottom where you plug in the power and data cables. The controller card is removable, and connects to the inner workings of the hard drive via contacts. No wires go into or out of the hard drive chassis so that the entire structure is sealed and dust-proof. The ribbed chassis of the hard drive is designed so that less metal can be used, while keeping the entire thing rigid enough to dampen out vibrations.

The openings to the hard drive are sealed with silicone gaskets for both environmental isolation and vibration reduction. Since external pressures may change, there is a pressure-equalization port installed into the top plate of the hard drive body which comes fitted with a filter. Apparently hard drives have an operating range of pressures, because air causes the read heads to hover slightly above the platters when spinning. Kind of like hydrodynamic lubrication…

To actuate the read head arm, which is machined from a single piece of aluminum, a copper coil is employed between two permanent magnets. When current is run through the coil, it generates a tangential magnetic force, which rotates the entire arm around an axis. I would never have guessed a system as simple as this could move the read head with enough precision to pull my MP3’s off a hard disk platter… but it does.

Unfortunately, I discovered that I didn’t have small enough torx screwdrivers to completely dismantle the hard drive. This means that I can’t really make a project out of this, unfortunately (though I do have a rather ugly one planned). The extent of my disassembly is documented on Facebook. Feel free to give it a once over. The design of a hard drive is surprisingly simple, but it’s been refined so well that immense amounts of information can be crammed economically into a single device.

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