Making inside cuts in wood are a bit more challenging than a cut that allows you to start from an outside edge. Not every saw can make such a cut. Add to that the need for curves inherent in cutting an oval and the challenge increases. As with most challenges in woodworking, cutting an oval in wood is simply a matter of having the right tool for the job. One of the best tools for making this particular cut is a jigsaw with a thin blade.
Measure your wood and mark the center of the area you want to cut your oval in. Lay an oval tracing template over the area and center it on the mark. Trace the outside edge of the oval template onto the wood.
Clamp the wood to your work table with the entire area of the oval hanging off of the edge of the table with clear space underneath.
Select a thin blade for your jigsaw with medium coarse teeth. Fit the blade to your jigsaw. Squeeze the spring clip to open the blade channel and slip it into place, releasing the clip to lock it in or loosen the set screw with an Allen key and insert the blade. Tighten the set screw.
Cutting the Oval
Select a drill bit that is large enough for the blade to fit inside a hole cut by it. Install it in the drill and tighten the chuck. Drill one hole just inside each narrow end of your oval. Drill holes halfway between the two end holes along the curve of the oval, inside the line.
Thread the blade of the jigsaw into one of the holes and start the saw, making sure that the blade is parallel to the outline of the oval. Cut along the inside of the oval line, staying as close to the line as possible. Cut around until you have completed the oval and it drops out.
Use a round rasp to remove any rough material to smooth the oval. Sand the edges with 80-grit sandpaper.