Every x-acto knife, scalpel, chisel comes to a point where it needs to be re-sharpened.
Every HDD eventually fails.
Every angle grinder disk will eventually get too small to actually grind anything.
With all these three simple assumptions verified in the same day and quite a bit of frustration, I began this project.
To turn that junk that was piling up before me in something useful: a small emery wheel of sorts.
BEWARE: angle grinder discs are not meant for sharpening, they are meant for cutting: every disk shows a warning that tells you to make contact with objects only with the side of the disk; touching the surface of the disk with an iron bar will result in it shattering and splinters wil fly around and you'll get hurt.
However, an angle grinder packs much more power than an HDD elecrtic motor. With this setup if you push to much into the disk, it'll just stop spinning.
DISCLAIMER: as usual, if you hurt yourself following these instructions, that's because you didn't know what you were doing, and not my responsibility. Use gloves, eye protection, body armor, and if you're not sure how to do something, just don't. Don't risk it, and don't blame me if something goes wrong.
Step 1: Open up
Here we have our HDD.
First we'll have to locate all the screws: a couple of them will be sealed away under white or "warranty void if removed" stickers.
Find 'em and remove all of them.
Open up, you might need to pry it open with a flat screwdriver, since many HDD producers use some kind of gummy stuff to keep the HDDs airtight.
Step 2: Strip it down
Now we'll have to remove everything we don't need.
let's begin by prying off the upper support for the heads mount.
Now, pushing with your finger on the copper coil you just exposed slide the heads off the disk[s] and unscrew the bearing with a large flat screwdriver. They'll come rigt off, but you'll notice that they still hang to the HDD body by a flat wire.
Unscrew the evntual screws keeping the flat connector down and pull hard to remove.
Unscreew the rare earth magnet and store it for future projects.
Unscrew the 3 screws that keep the disk attached to the motor, and set aside along with the small disk, then lift off the main disk.
Step 3: Add the disk
The angle grinder disk will not fit on the bearing, so we'll just lay it on and screw the small disk back in place.
Step 4: Power on
now you need to get power to the HDD.
I used an adapter that I had lying around in my wiring drawer, but you can also power it up by shorting the green wire with a black wire on an ATX power supply.
so plug it in and watch it spin!
Step 5: Grind away!
Here you have it. now you'll be able to sharpen scalpels, chisels, x-acto knives, regular knives, scissors, drill bits, coins, anything!