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If a major disaster occurs and SHTF, some people assume this would mean returning to a “stone age” level of technology. However, that's not necessarily the case. When the power grid is down and everyone else is preoccupied with finding food and shelter, it'll be possible to scavenge lots of abandoned electronics. Even now, there are plenty of people throwing out old computers every day. Fortunately, if you're patient and willing to tinker, you can re-purpose these electronics into useful tools.
Old hard drives are an especially common form of electronic waste. These disks may seem useless outside a computer, but don't forget that they have a powerful brushless rotary motor that's capable of anywhere from 5,400rpm to 10,000rpm. If you don't care about the data on the drive, you can harness this motor to create a hard drive rotary sander.
Here's an example of a hard drive sander in action:
Obviously, there are many uses for this device, from sharpening knives to crafting arrowheads and other tools. To make your own, you'll need an old hard drive, preferably with a 4-pin MOLEX power connector, as seen below. Newer drives with L-shaped SATA connectors will still work, but they may require soldering your power source directly to the drive's motor.
You'll also need a screwdriver with Phillips and Torx bits to open the drive case, some sandpaper, glue or double-sided tape, and a power source. The power source is the only tricky part, as it needs to provide both 12V and 5V DC power. If possible, you should scavenge a computer power supply that already has this plug-and-play connection, as seen below:
Note the pinout diagram in the bottom right corner. If you have access to power from a wall outlet or generator, this computer power supply will be your best option, as you can simply plug the power supply into the wall and hard drive, and switch it on. If not, it's possible to power the sander from a portable 11.1V to 12V lithium battery pack, as seen in the video below:
This device won't be as powerful as a purpose-built sander or angle grinder, but it also won't be as desirable as those tools, since it's made out of discarded junk. It's also relatively quiet and can be used on a workbench for detailed tasks. So, if you're ever thinking about throwing out an old computer tower, you might consider re-purposing it into a hard drive rotary sander.