The problem with an oval is that its a circle with two centers or an ellipse in which you have two back to back parabolas with dual opposing foci. In some cases, its hard to tell the difference. In other cases, the ends are more football shaped.
In either case, this exercise presents some frustration to folks. Frustration both in terms of layout and an in terms of execution of the final shape.
Fact is, I have found that one of the best ways to complete this problem is to use a run of the mill router equipped with a Micro Fence Circle Jig using the Ellipse option. Micro Fence produces awsome tools and their contruction and execution are OLIVER-IZED!
Nobody cuts a circle or ellipse or oval as well as the Micro Fence system in terms of setup, ease of use, accuracy and first time use success. Its worth checking these guys out. They often keep a lower profile than they should.