Here is the diagram to cut the wedge pieces to. It is scaled to 96 pixels = 1 inch. The outside of the wedges corresponds to the outer flat lines. The ellipses are the finished shape of the porthole frame. To use this, print out this page. If necessary, use the enlarging or reducing feature on your photocopier to get the inner dimension of the ellipse to 5" wide.

Notice that the segmentation lines are offset. More about this later.

I used this program to generate the diagram.