This jig uses a wiggle board to fit into two complementary pieces of wood. The wiggle board is 3/16" crosscut plywood.
Decide on a desired shape, then mark it out on the board.
Cut out the shape with a jigsaw.
Fit the wiggle board into the shape (Image 1). Then, do a dry run to make sure there are enough pieces of wiggle board and that the shape fits properly.
Glue the pieces of the wiggle board together and fit into the template shape.
Clamp the wiggle board into the template (Image 2).