There are several ways to make rosette channels from a simple hand held trammel and chisel to a purpose built cutter. I do several a year, both for my own instruments and the classes I teach, so I use the latter from LMI. There are others available such as one from Luthier Tool. The LMI setup is kind of a pain to set up initially but once set up works very well. I’ve used several products from Luthier Tool and while expensive, they are beautifully made and easier to initially set up.
The problem is the small rosette and sound hole for the harp. It’s two inches plus and will not work with the conventional cutters. For this one I took a simple General circle cutter, re-ground the cutter to my rosette dimensions and replaced the center drill with 1/4″ drill stock with a bearing fixed to the top. When the depth of the cutter is fixed the bearing stops it at the proper depth, much the same as the commercial cutter.
Now the back and top have to be fitted. I use binding that is a full 1/4″ so that I can cut out the sides and let the main braces of both the top and back run through. I feel this makes it easier to keep everything aligned. Of course, if you are doing a style of guitar without the binding like a Dyer Style 4 you have to inset the braces to the sides because there is no binding.
I always put the back on first so that I can facilitate clean up of any glue left in the joint between the back and the sides. I use a slow set Titebond and spool clamps to joint the surfaces. To quote Wyatt Earp “Take your time… in a hurry.”
Before I glue the top to the sides, I make sure the sides have not deformed. If they have I sand them again to the proper radius. I then repeat the inletting for the top braces to the sides and glue the top on.
Next time: Binding and finishing.