Guys those who interested to make a simple grinder for small scale use can try this....
All you need is an old HDD, can be easily get from a computer shop.

Step 1: Parts Required

1. Old HDD
2. 230Ac - 12v, 2A circuit board (you can also use 12v,2A step down transformer or SMPS)
3. Emery Sheet
4. Push button type micro switch
5. SPST switch

Step 2:

Open the HDD & remove front cover,actuator & magnetic disc.

Step 3:

Now take the magnetic disc, cut same size of emery sheet & stick it on the disc.

Step 4:

Place the hdd & circuit board on a plastic box.
attach the push button switch & spst swich on the side of box.

Step 5:

HDD has a tendency that when there is no usage the spindle will automatically turn off. So to get a continues spindle rotation just short "reset & ground" pins on the ide port. To identify the pins look at the picture.
Connections from these pins are given to push button & SPST switch