I am scratchbuilding an F7a loco. and I had problems locating drawings of the windshield. After days of hunting on the web without results, I located a full scale F7. I then got some cardboard and traced the full scale shape, because I was tired of trying to reproduce the correct shape and failing. I am now in the process of transferring the shape into CAD. After trying to capture the gentle curves, I have come to conclusion that the shape was drawn from french curves. I am transposing the curves into meaningful arcs. So far I have about 20 arc center points, but I think that the shapr will be very accurate, probably within 1/8th inch of full scale. If anyone would like to discuss my endeavors or have info., I am all ears. Thanks Rbrown.