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Probably a dumb question but I am confused about when in the process of thinning the guitar top do you rout the channels for the rosette and install it?
Seems like you would need to do this after you thinned the guitar top somewhat since most rosettes aren't that thick ( 3/64 or so ) but maybe not to it's final dimension.
I'm guessing you would thin the tops to say about 1/8 inch and then rout the rosette channel and install the rosette.
After this, you would then finish thinning the top to it's final optimal acoustic dimension.

Is this correct?
Any feedback appreciated.

Scamp

Hey Scamp. It depends somewhat on what type of rosette material you re using amd I’m assuming a spruce top. If using 0.060” or greater thickness fiber or plastic rosette material it’s not so critical. If using an abalone AbLam, you have to be more careful sanding the exterior so as not to sand off the laminated surface.
I usually run both the inner and outer sides thru the thickness sander to take care of any humps or bumps down to about 0.140”. Then install the rosette and sand the exterior just until the top is uniform and the rosette is flush. Then I turn it over and remove any additional material from the back side until the flex and tap sound good. On the one I just did, that was in the 0.110” area. I’m not sophisticated enough try thinner edges like some do.

You’re on the right track, I believe. Hope this helps, but as always, your mileage may vary! 😎

For me I get the top surfaced and will do my rosette what the top is thickest. This gives me chance for corrections. You can always make thinner you can't make thicker

After my soundboard has been thinned and shaken till I think there's no more improving it, I cut the rosette channel and install the rosette. A few passes with the RO sander to level the top around the rosette, and it's off to cut out the soundhole and get on with the bracing and trimming to rough outline.

I plane both sides to check which will be the 'show face'. Install the rosette and level. The rest of the thicknessing comes off the back of the top.

I would say that it’s probably best to inlay the rosette first, then thickness sand/plane it.

I’ve done the opposite and sanded through a rosette I worked really hard on.

Finish sand the back of the top. Measure the thickness of the rosette, and your top, and decide how deep you need to cut the rosette groove. If you have a 0.1" thick rosette, it just becomes a question of how much top thickness you want to leave at the bottom of the groove. If you have an "eBay special" rosette that's 1/32" thick and a bit wonky, you have to figure a lot closer.

What we do is driven by the tools available and the abilities of the builder. Not every technique is available to every builder. I-did-it-this-way may be fine for the speaker but may be inappropriate or inaccessible for others. Few builders have thickness sanders (the one I use is five hours down the road, two states away). And my rosettes come with chopsticks. And I've had no problem routing a .030" channel for the rosette and touching up the surface with a RO sander. For me, next step.