I always begin a build with the sound board. First you join the wood, then you cut the groove for the rosette, then you cut out the sound hole. Here is how I do it.
With a router, guided by this 1/4 inch thick guide I made, I first cut the rosette groove. Then the soundboard is repositioned and the sound hole is cut. The sound hole is not cut entirely through the wood but when this raw soundboard is sanded the "almost through' cut will be released and the sound hole will fall out.
Here is the raw beginning. The grooves are cut, the rosette groove shallower than the sound hole cut. I will install the rosette and then sand the soundboard down to its final thickness. In the process, the ugly glue line will disappear and by sanding from the back, the sound hole will fall out and reveal itself.
