I happened to be across from a local auto shop / junkyard when they had a big scrap metal hauler come to pick up some junk cars, and their crushing technique was hilarious. All they did was repeatedly pick up a big chunk of granite about 6' long, maybe 2' in diameter, and drop it on the car, over and over. Then they'd just pick up the flattened remains and put it in the truck. Interesting to see the difference between a little dodge neon and an older volvo-lots more drops on the volvo to get it really flat... Just wish I had a camera with me!!