I cannot possibly stress enough that YOU SHOULD NOT DO THIS. That said, enjoy watching a yoyo with razor blades destroy everything in its path.
(History lesson: first razor blade yoyo was created by Mark Faje, a juggler from Chicago who does a lot of stuff with knives in his show. I made my own and nearly got disqualified when I used it in my freestyle at the 1997 World YoYo Contest. Stupid things like this have a long and glorious history in yoyoing. Once again: DO NOT TRY THIS AT HOME.)