Look what I did to your hard drive! - this can serve also as a nice prank.

Recovery of data not guaranteed (aka impossible). 

Why HDD grinder? 

If you don't have full workshop and you just need to sharpen a drill bit or, round edges on anything it comes handy.

The 3D model fits to any 3.5" HDD, as the holes are spaced always the same way.

Anyway STEP model and Fusion360 source files are included for easy editing!

Material

• an old 3.5" HDD
• Control board (this works with 3-pin as well as with 4-pin motors)
• 3D printed frame
• Power connector (I used 5x2.1 barrel DC jack with 11mm mounting hole)
• Some cables

Guide:

1/ Get old HDD

Get 3.5 inch HDD, strip it off everything instead of motor, plates and chassis.

2/ Add sandpaper

Use double sided tape to tape sandpaper to the disk. Sandpaper cannot protrude from the edge. I used exacto knife to cut it all around.

3/ Connect control board

If you have 4-pin motor, identify common wire using multimeter. 

For 3-pin motor you can connect in any order, then switch 2 wires if CW/CCW does not fit. 

4/ Test

Connect power supply and test. I use 12V. My motor sometimes needs a jump start. If it is turning too slow, torn it off, rotate by hand to another direction and only after then connect power. 

5/ Put it all together

• control board
• printed frame
• threaded inserts
• power connector

For control board attachment, I used threaded inserts for M3 bolt. The HDD is bolted using original bolts (be aware, these are not metric). 

Add: Chassis mod

Optionally, you can cut out a section of chassis, to have better access for griding something small.