I didn't get any responses to the previous question but it's just as well as I have changed the plan slightly. I am going to build the doors with 2"x4"s planed down to 3" wide and they will be on edge. The finished doors will be 4-1/4" thick.

I am planning for the doors to seal on the inside faces, and will likely have an astragal on the outside as well, so I am not too worried about getting a good seal. I just don't want to make the gap between the doors any wider than necessary, and would rather not angle the inside frames.

Does anyone know a good rule of thumb to use (that doesn't require trigonometry ) to figure out what the gap can/should be between the doors so they will close properly? I want to be able to open/close them independently. The doors will each be 36" wide.