It's for 125mm sand disk and I find it very useful for small woodworking and 3D printing.
Step 1: Materials
You will just need to buy some round sand paper with a sticky face (3$).
Step 2: Cut the Drill
A friend gave me this drill because the battery was dead. I didn't want to change it because it doesn't worth it: the drill cost 15$ new. In the dead battery some accumulators were dead but 5 of them were not so I take them for a future project.
First disassemble the drill and take off the motor and the switch. Reassemble the 2 plastics parts and cut the handle. Cut the wires of the motor and solder 2 longer wires to it. Put back the motor into the plastics parts and drill 2 holes to pass the wires. Screw back the plastics parts and then remove the chuck.
Step 3: Make the Holder for the Drill
To raise the drill I use a big piece of wood. To hold the drill in place on it I use a large piece of aluminum, I cut it, and screw it at the end of the drill. I then screw the piece of aluminum on the wood piece with 3 screws. I screw 2 more screws on each side and attach a copper wire around the drill to avoid any movement.
Step 4: Make the Base
For the base I use only small pieces of mdf wood. I first cut the bottom part. I cut 3 more little boards for the stand, glue them on the bottom piece (use some clamps to hold them tight).
Step 5: Make the Disk
This disk is where the sand disk will be stick. It has to be attached to the shaft of the drill. I cut it with my dremel. Because it wasn't perfectly round, I turn on the drill and sand the edges of the disk while turning. This makes the disk round and creates less vibrations.
Step 6: Finish the Base
Drill 4 holes under the base for fixing the holder of the drill. Then cut the stand and glue it in place. The end of the stand must be as close as possible with the sand disk. It has to be perpendicular too.
Step 7: Connect the Motor
The drill works at 12v and 3 amps but the start peak current is about 10 amps. So I power it with an atx power supply. If you want to change the direction of rotation, inverse the polarity.