Very nice machine. There were some Werthiem machines with hand cranks. I don't know how they were attached. I'm guessing that it would be extremely difficult to find a hand crank that will work for your machine. I know Singers had a motor boss on later machines that would be used for attaching a motor or a hand crank. I don't see one on yours. I'm also thinking that the distance from the pillar to the workings of a replacement hand crank would be different from what would be available today as I think the modern hand crank would be too short to work with your machine. I tried putting a hand crank up to a couple of German machines I have and even if i could figure out how to attach it, it would not work as it would not go far enough beyond the hand wheel to all the wheel to turn. Your mileage may vary.
Janey - Neat people never make the exciting discoveries I do.