Using a file to cut gears doesn't take a lifetime, they even did this in one of the documentaries about the subject. https://youtu.be/5mIGJzqrGnc?t=36m9s https

Using a file to cut gears doesn't take a lifetime, they even did this in one of the documentaries about the subject. https://youtu.be/5mIGJzqrGnc?t=36m9s https://youtu.be/5mIGJzqrGnc?t=36m9s