Tools and Supplies:
Dremel Moto Tool 4000:
Dremel Router Base
Titebond III Glue
Portable Block Sander
Plastic Tipped Hammer:
Plastic or Wood Purfling
Plastic Push Pins
Acoustic Guitar Rosette Assembly:
For an acoustic guitar first assemble the rosette rings. Utilize the rosette ring design directly off the guitar plans as a starter or seed drawing. Optionally design a rosette and make a form for the center rosette if it is to be built up from layers of purfling. The form should match the inside diameter of the rosette. Note that the rosette form consists of a 1/8″ thick wood disk that is fastened to a plywood base.
Measure the length around the rosette form and cut the purflings so they wrap around the form and leave about a 1/2″ gap at the top. (this gap will be covered by the fingerboard). To keep the purfling from sticking to the form, apply parafin wax on the form surfaces or install the form and the purflings on a piece of waxed paper.
Take the wood or plastic purfling and apply the appropriate glue. (Titebond for wood and Duco Adhesive for plastic.) Start at the top of the rosette, which is the portion that will be beneath the fingerboard, and slowly form the purfling around the form, using either plastic push pins to hold it firmly against the form, or small finishing nails using a plastic tipped hammer. Continue this until the top is reached. Set aside to dry.
Layout the rosette precisely on the soundboard plate using a compass. Drill a hole in the soundboard at the center of the rosette radius. Insert a bolt that matches the Dremel Router Base Hole through the Workboard and fit the soundboard over this bolt. This should be a tight fit. Now chuck a carbide or diamond router bit in a Dremel and attach it to the router base. Double-check all of the cuts and work slowly. Be especially careful when routing almost parallel to the grain as the bit can tend to tear out some of the soft grain. Your cut depth should be about half of the top thickness. I usually use a spiral down-cut bit for this cut.
Remove the rosette from the form and carefully check it against the routed channel in the soundboard. It should be a tight fit and the rosette should not just drop into the channel of the soundboard. It should require light tapping with a plastic tipped hammer. Once you have the routed channels exactly the right widths, apply adequate glue to the rosette materials. Again, use titebond for wood and Duco Adhesive for plastic and do not use too much glue. Tap the rosettes until they are protrude very slightly above the top surface of the soundboard. Set aside to dry.
When dry take a very sharp scraper and cut the rosette down to the surface of the soundboard.
Classical Guitar Assembly:
If you purchase a pre-made rosette, carefully mark the inside and outside directly on the guitar top plate with a compass. Using the Dremel and a router base adapter, cut the rosette channel. The depth should be slightly shallower that the rosette depth. Again, check the fit several times. You should have to lightly tap the rosette to get it to fit into the channel. It should not drop in without any force.
Once fit, apply a small amout of Titebond glue and fit seat the rosette with the plastic tipped hammer and a small block of wood. Set aside to dry overnight. Take a very sharp scraper and scrap the surface of the rosette level with the surrounding guitar top plate.
One final operation to do while the soundboard in still on the assembly board. Use the router to cut out the sound hole. Make the cut with 2 passes minimize wood burn and go slow.