Why don't you use a CSG-merged torus with cylinder?
Scaling the torus could smoothen the curvature near the
flat area... Ah, but then the curvature at the rim would increase...
Try using a lathe with some splines. I'd think you'd have enough
freedom to create the shape you are looking for, and calculating
the splines for spheres isn't very difficult.
--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
