What evidence is there that seances work?

I've used one myself with one of my friends, homemade. We used the top of a Pizza box. We looked up how to make it, and did. We turned off all the lights, lit some candles, spun the planchette (in our case the clear top of a hairspray can) and placed one finger on it each. We asked if anything was there. An unexplainable forced moved the planchette to yes. At first I thought my friend was moving it, but as we kept asking it more and more questions, the planchette was moving in directions my friend couldn't have moved it with one finger without messing up. It was an amazing experience, but not scary, as most people would think.