A jointer is the best tool for flattening twisted, warped boards. But what if you don’t have a jointer or the board is too wide? Set the board on a “sled,” a flat piece of 3/4-inch plywood. Then shim the high corner(s) so the board doesn’t rock. Also shim high spots in the middle of the board. Mark the shim locations, remove the board and hot glue the shims into place. Then glue the board to the shims and the plywood with a dab of hot glue. Send that rascal through until it’s flat, then pull it free and plane down the other side.