If you are asking how to layout the oval, I have some information written down out in the shop that I can retrieve for you. I use a string with a couple of nails on the major and minor axes. You remove one of the three nails and hold the string tight with a pencil as you mark the oval. I used to know how to explain this method without my notes, but time has taken its toll...
If you take a ruler and draw a line from one focus to any point on
the perimeter of an ellipse, and then a second line from that point
back to the other focus, the total length of those two lines is a
constant, independent of which point on the perimeter you choose.
This gives you a simple way of drawing an ellipse. Take a wooden board,
and hammer in two nails to represent the foci (plural for focuses, not a dirty word or a Star Wars critter). Fasten one end of a
piece of string to each nail, then push a pencil against the string
and draw the ellipse keeping the string taut at all times. You can
draw ellipses of different eccentricities by adjusting the length of
the string relative to the distance between the two nails
Yep. I'd put the string (actually I'd use something a little stouter than just some random twine. Perhaps a thin metal cable (stranded) with a crimped end?) around the body of the router and the two foci (?) pins. You pull the cable taut and it'll inscribe an oval automatically. You'ld have to let the cable slip and slide a bit on the foci pins, but that should work.
I'd draw it first, then bandsaw it to get close and then router it to get the finished edge. That way you're only going to take off 1/8" or so.
You guys did an admirable job of describing how to draw an ellipse, but that man asked about an OVAL! An ellipse is ovoid with different radii at each end. An oval has equal radii. To make an oval, draw 2 identicle circles and connect with straight lines.
Hmmm...ok...you have driven me to confusion on these terms...(yea yea...I know...it was a short drive )
When I used the described method, I had the nails on the scrap nearly as far apart as the table was wide, and moved the board into position so that the string (and pencil) would reach the end of the table in the middle of the arc (at the top of the arc eh). Drew the ellipse, oval...whatever, then repeated this for the other end of the table. Since both ends were (basically) equal, what was it? Oval?...or an ellipse?...or a table with rounded ends? I'd like to call it by the correct name eh....
The string technique for geometrically constructing this type of shape, always makes an ellipse. As far as an oval, I am not sure about the proposed definition of an oval, there are many types of ovals, the extended circle idea, along with other mathematical and non-mathematically described enclosed curves. I have stayed out of this one due to the differences in what is asked versus what is wanted.
You've got to have a college degree in mathematics to know there is difference between an oval and an ellipse. I guess I want to cut an ellipse after all. I guess MadMark's suggestion is the way to go, "mad" as it may be. I just can't figure how to make the metal string run around the router smoothly enough for the cut to come out right. The metal string will have to be tied together to get the right length, and won't the knot cause a bump when it goes around the Router.