Here are the backs just setting on their respective bodies. They are all curved and hollowed to the proper thickness. They are ready to glue to the bodies, but the bodies are not yet ready to receive them. I flattened the underside of the backs on the thickness sander before I hollowed them out so they sit nicely on a flat surface, But the bodies are not yet flat. Getting them that was is the next task.
The underside of the body is sanded perfectly flat on this large 25 inch sanding disk that i set stationary on my table saw. I simply grind and grind on the back of this instrument until it is perfectly flat entirely around it's perimeter. Then the back will fit perfectly and back and body will be glued to one another. Seems like it takes forever to do this simple task but it is necessary if you want a perfect joint.