If you want to cut plywood circular disk or to cut a hole in it large diameter, it is not necessary to have a special cutter or a jig saw.
Take a wooden bar and two grozda. One beat her to speaking on the sharp end was in the center of the proposed circle. And the other needs to get out of it on the line the future of the circle: when rotating the slats it will be to scratch the plywood layer by layer until you cut through it.