I didn't have a big enough single piece of wood to make a rosette that matched the back and sides of the guitar, so I used the offcuts from the back.
First pic; I've made a workboard with the rosette laid out. I've cut 16 wedges making sure the grain on all of them points towards the center - this will help hide all the joints. The wedges don't have to all be exactly the same, I wasn't too concerned with length for example, just that the sides to be joined were all at a similar angle. The longer they are the more support you'll get for your router base.
Then I sanded them, trying to maintain the angle, but the most important part was matching them to each other without any gaps.
I used titebond and rubbed the joint trying to minimise any gaps, it worked quite well and I only needed a small piece of tape to hold each wedge down. Note that I've used some anti-stick baking paper stuff underneath to stop it sticking to the work board. As the wedges aren't all exactly the same I simply tried to make the edges match up roughly with the layout lines on the workboard. The last wedge obviously wasn't going to fit perfectly without an adjustment, but nobody will ever know that I cheated.
Once the glue dried I removed the tape and stuck it back on the workboard with double sided carpet tape and ran the whole thing through the thickness sander. I'm not going to go into routing channels 'cause I expect you all know how to do that.
Sanded flush, and then reset the router depth to cut right down to the workboard.
Splash on some Shellite (naptha) to release the double sided tape, break off the waste and try to peel off the ring without breaking it. The joins pretty much disappear at this point.
Done.
