Try to salvage little electric motors from scrap, because you can usually find a way to reuse them. I don't remember where this motor comes from, I've got it many years ago when I used to dismount everything I bumped into, anyway when I found it the other day I immediately pictured a small bench saw to cut metal. Not wood, because motor has a belt and a ratio so that the gear turns at a speed of about 600-1000 RPM which is good for metal, bricks, stones but wood needs very fast speed. To cut these materials you can use a disc grinder, so I bought a pair of discs to apply to my motor.
[UPDATE] I also can apply a disk of sand-paper if needed. To check speed of the disk see last step.
Step 1: Motor and pulley
I already put together motor, pivot, belt and gear with a wood block when I was a boy, so I left that mounted. The pivot is a very sturdy steel beam and at that time I drilled an hole in the wood and I wedged the pivot into it. The gear has not bearings but uses a metal bushing to rotate around the pivot. The mechanism you see around the little gear on the motor pivot is meant to release the rotation when motor stops, anyway I don't need this feature.
The motor has 30W power, and with this gear the final disc has a very strong cutting force.
Step 2: Finding a fastening
To attach and change easily the discs on the gear I needed a simple and effective way. After some research I retrieved a piece of hydraulic pipe and a cylindrical nut. Since the pipe's external diameter is almost equal to the disc hole measure, and the pipe fits very good on the gear's steel pivot, that solution works perfectly. I only had to glue with two-components adhesive the pipe on the pivot, adding a plastic ring where discs will be pushed by the cylindrical nut. This nut is very easy to tight by hand, and changing the disc will be fast.