https://www.instructables.com/id/Recycled-HDD-Powertool-Disk-of-Prometheus/
The new instructable is here. Its ia newer, improved and hugely better version and adresses the disadvantages of this design.

If you are a computer guy, you must have lots of Hard Disk drives piling up. If you want to use these for a good reason, the HDD Sander is just for you.

Because of the high RPM platter motor , the HDD platters have enormous speeds, generally from 5000 RPM up to 15,000 RPM. To make use of this power, The HDD Sander attaches directly to the platter, in a portable and interchangeable design.

A quick video of the HDD Sander in action is below.It was taken in the dark and looks excellent, due to the sparks coming from the sander.

WARNING: The HDD sander is not a plaything. The platters are spinning at a very high speed, making it easy for the sander to rub your finger raw. I am not responsible for any damage you do to yourself or to anyone else near you.

UPDATE 1: Some users have pointed out to me that their HDDs are just not simply spining up. To make them, sometimes you need to adjust the jumper blocks on the back of the HDD.See Step 4, Picture 1 for help.

Step 1: Materials

Most of the materials for this project have been recycled to keep the cost down.

1.An dead HDD - From a old Presario ($0)
2.Sand paper(any grit) - $5
3.A bench-top Power Supply/12v power source - ATX conversion ($0)
(Search for "ATX bench-top Conversion" on instructables)
4.Molex Power Connectors - $0 (recycled from old PSU)

Thats it, thats all you need for the HDD Sander. I expect you to have a few basic tools like a pair of scissors and a wire stripper and a screw driver with a Torx T9 driver head.

You'll also need an compass to make the sand paper template.

Step 2: Dissasembling the Hard Drive

Thats the boring part done, now lets start voiding some warranties.The model we will be dissasembling is an old Seagate.

Firstly, make sure the HDD can spin up by connecting it to an computer and listening to the spin-up.If it spins up, continue, if not, check the power connectors.

Start by peeling off all the stickers on the body of the HDD. Particularly the ones with "WARRANTY VOID IF SEAL IS BROKEN"

This will make all the Torx screws visible.
Unscrew all of them, on the side with the steel shield which protects the HDD. Don't unscrew other side, the one with the PCB. We will require the PCB side for the HDD motor controller.

Even after you unscrew all of the screws, it will seem as if the shield is still attached to the body.Inserting a flat blade screwdriver head into a gap and pry it open, very gently.

After doing this, put the shield away and behold the guts of an HDD.

You will see 3 things. The HDD platter, the actuator head and the powerful rare-earth magnet.Unscrew the magnet from the body and keep it for future projects.Also, slide out the actuator head and also store it.

Now that we've finished disassembling the HDD, you can now only see the dominant HDD platter. That is he most important aspect of the HDD Sander.

Step 3: Cutting and Fitting the Sand Paper

The sand paper needs to be cut down to the size of the platter so that it can easily fit into its place and can be removed if necessary.

The technique used to cut the template from the sand paper is simple. Firstly, use you compass to find the disance from the centre to the edge of the platter.

Then, use the compass to draw the circle on the sand paper.

Do the same for the inner circle, and find the distance between the center of the steel disk and its outer edge. If you are confused, see the pictures for help.

Then, with a pair of scissors, cut out you template and check if it fits on the platter. Trim the edges as necessary and don't keep too much slack on the center edge.

After trimming, gently ease the sand paper onto the spindle(see video)

Step 4: Finishing It All Up

To test whether your HDD sander works or not, you will have to cut the Molex connector,strip it and connect it to your PSU/power source. connect the Molex as shown below.

RED BLACK BLACK YELLOW
+5v gnd gnd +12v

Plug the Molex Connector into your HDD, turn on your power supply and watch it spin up.

If you are using an alternative power source, remember that you will need to give exactly 5v and 12v to the Molex.Otherwise, the HDD's controller will not start due to power deficiency.

You will also need to supply about a total of 2 watts to the 5v and 12v lines.The wattage depends on the RPM of the HDD motor.Generally, this rating is printed on the large sticker covering the metal RF shield.

That is why this project is much easier with a benchtop variable voltage PSU.
The PSU can provide the HDD the current it needs by monitoring the current draw of the HDD.

Picture 1 courtesy of 'www.pcguide.com'

Step 5: Tests: Grinding

TEST 1 : GRINDING WOOD

The sander performs very well and smoothens down the wood quickly.See video for the demonstration.

TEST 2 : GRINDING STEEL

The sander effortlessly grinds through the steel, although better performance would be reached with specific, black steel grinding sandpaper found here: http://www.hartvilletool.com/shared/images/products//large/29887.jpg

Step 6: Tests: Sharpening Knives

With the high RPM HDD Platter, you can sharpen knives easily.

The folllowing videos show 3 stages: before grinding, being ground, and after grinding. The end result is quite pleasing.

BEFORE GRINDING:

GRINDING:

AFTER GRINDING:

P.S - The 2nd video shows and good technique of sharpening the knife if you have never sharpened one before.

Hope you enjoyed. Post lots of pics if you decide to build one and don't forget to clean the sander's insides with a fine camel-hair brush, once in a while after using it.

If you like it, subscribe to me for some interesting builds. Rate me too :)

Kabir