This will show you how to make a piranha type tool with a cheap knife and cutting board.
Step 1: Base
I was looking at the pirrahna gear tie tool thingies, and thought they were really sweet, however I'm broke so I had to come up with something on my own. The shark was born. This project is super customizable, so be inspired, feel free to use power tools, I don't have those, so I didnt, but it would probably look better. Also feel free to vote for this in the before and after, reuse or outside contest (PLEASE BE SAFE, I'M NOT RESPONSIBLE FOR ANYTHING DUMB YOU DO WITH THIS.)
What you need...
-crappy plastic cutting board
-not crappy epoxy
Step 2: Blade
Step 3: Body
Here is where you can get creative, cut a four inch strip of the cutting board, then cut it in half, from here you can use whatever design you want, just make sure It has a slot for the blade, similar to a seat belt cutter. Now, trace your design on the other peice of cutting board, and cut it out, the blade will go in between these.