Acoustic Guitar Construction

I have run into a conundrum that I was hoping you might be able to help me figure out. I'm in the planning stages of building a Martin C-3 (circa 1932) from plans I bought from GAL. I went to Chicago Music Exchange and they let me play a 1937 C-2. I was duly impressed by the marvelous sound of this guitar, which inspired me further to pursue my plans with the C-3 build.

However, one of the differences between the early C-3 and later C series arch tops was the use of a circular sound hole rather than f-holes that are found in the later models.

Now, here's the problem. I have a jig to cut sound holes and rosette channels in flat soundboards, but I haven't got a clue how to reproduce a perfectly round routed cut in a carved arched top. Cutting the sound hole before carving the top might work, but that doesn't seem to logically follow for the rosette channel because the depth of the rosette channel has to vary precisely with the curvature of the top. Also, it seems that cutting the sound hole before carving the arch would present chipout problems during the carving process.

Is there an easy way to do this that I'm just not seeing, or am I in over my head?

For this one I suggest that you put the power tools away --- you'll need a drafting compass loaded with a Grifhold #24E blade and a small sharp chisel to clear the channels --- the picture below gives an idea of how the process works. Note the reinforcement to maintain the center location. Not as daunting as it looks and its really an enjoyable procedure. The blade will leave a slight bevel take that into account when setting up reverse the inner and outer cut directions so a toe-in channel is created. Cut a little deeper then you think is necessary and work slowly and all will be good.

Thank you Ken. Now I'm pumped to get started. I have a great drafting compass and found the Grifhold #24e online. Sadly, I have other projects in the pipeline ahead of this one.