Okay folks, lets have a go at that circle with a router.
#1 Get a #6 finish nail and cut the head off it.
#2 Take this headless nail and chuck it up in your drill.
#3 Measure, then mark the spot that will serve as the center point of your circle (the radius). I am measuring to 4 1/2" from that cutting edge of the router bit that will be cutting the circle rather than the other side of the bit that would be cutting the hole. In this case we are making a 9" circle.
#4 Drill the hole and insert a nail so as to be able to mark the drilled hole on the top side of the plate. I mention this for those who have more than a few holes drilled in the plate.
#5 Insert a nail in through the top side of the plate and put it's point into an indentation made in the center of a piece of 1/4" plywood.
The plywood needs be secured so as not to move. The strips which raise the plywood off the work surface need be secured too. Visual clarity can be seen in # 9.
#6 Start the cut and rotate counterclockwise. Be sure the nail is driven securely into the piece you are cutting. Try being aware of the twisting of the cords, the depth of cut and other things that may cause a problem. Be alert and aware of your surroundings.
#7 Continuing the cut, just a little bit deeper.
#8 Plunge deeper still.
#9 Here is a look at the finished circle, cut and still secured. Notice the center nail hole would be set into the center 3/4" plywood strip as well as the 1/4" circle. Notice the screws are set away from where the router bit path is. Here we have a 9" circle and a 10" hole.
#10 This is a photo of the 9"x1/4" circle fitting into a previously cut 9" hole.
So far so good?
Shaz