The first elongated coins are thought to have appeared during the 1892 World's Columbian Exposition in Chicago, commemorating the 400th anniversary of Columbus's voyage to America. Ever since, coin-flattening machines have become a popular attraction at fairs and malls across the United States. Many have wondered how they can flatten coins at home--and if they can do it legally. Altering and defacing American currency is illegal, but only if it is done with fraudulent intent, so if you choose to flatten a coin by one of these methods, do not then attempt to use it as currency.
Set your coin on a hard surface, like an anvil. Hit it repeatedly with a heavy sledge hammer, taking care to hit it in the same spot. Wear protective eye goggles, since the coin may accidentally shoot out at you.
Put your coin on a train track and wait for a train to run over it. Stand far away from the tracks until the train has passed, and move away again quickly once you have picked up your coin. Be aware that the coin could shoot out from under the train, so stand clear.
Go to a fair, amusement park or mall and look for a coin-pressing machine. Put your coin in the slot and turn the crank. You can also purchase your own coin press for about $6,000 online.