THIS IS SIMPLE ENOUGH, just reset the depth of the cut to the thickness of the top, reset the pivot pin through the top and into the support below. Set the router to cut the diameter you choose for the sound hole- and VOILA!
Lift out the circular center - and
You have a sound hole, a rosette and a finished sound board--Oh Hold it a minute, this soundboard will need some bracing.
Here are the rough braces and the approximate positions they will take on the back of the sound-board. After lots of shaping of course,