Hello ladies and gentlemen, and welcome to my new Instructable.
I will quickly cover the main steps on how to make a simple sander / grinder using a hard disk.
That's kind of out of focus, but look at those sparks. Yummy scorching particles.
Step 1: Open It Up
I chose a 7200rpm HDD. No particular reason, any will do.
The tool will be powered via the Molex connector, I adapted a power supply some time ago, which now comes in very handy when I want to move this little beast around, click here to see it: Molex PSU.
Simply open the hard disk with a Torx screwdriver (usually, size 7 and 8 are ok).
Remove te heads and the internal electronics, only leave the motor and the plates.
Cut a disc of sanding paper the same size of a plate.
What you have to do is to rearrange the plates and the spacers so that the sandpaper has the sturdiest base. I personally stacked them this way: plate - plate - sandpaper - spacer - holder.
Step 2: It Already Works Well, But...
...if you want to use it at the top of its capabilities, cut the base and the lid as shown in the pictures.
The lidded part allows to grab the sander and use it on objects, as the "blade" is now unobstructed by the frame.
You may also add a PCB protection. As you wish, it works anyways.
Step 3: Unexpected Problem
There is a little problem, the hard drive shuts itself off after a minute to save energy. I don't know how to prevent this, so I added a switch on the 12V line that allows me to turn it off and on without losing spinning momentum.