I have developed a way of making spiral rosettes, which you will see on some of my instruments. In the current build set, one customer wanted a spiral rosette on his guitalele, which has a baritone size body. I did not have a baritone sized rosette template, so I had to make one, and in the process figured I would illustrate the process.
The local community college has a wonderful place called the “Fab Lab”, as in ‘fabrication’. They teach courses in building all sorts of stuff, and have complete wood and metal shops. After taking a course, members of the public can come in and use the equipment by the hour. The piece of gear which I use is a large bed laser cutter. It will cut 1/4 in acrylic just fine, with thousandths of an inch accuracy. One does the design in Corel Draw, which I do at home, take the drawing over on a thumb drive, and then simply ‘print’ to the laser cutter. Red lines in the drawing cut, and black lines engrave on the surface of the acrylic.
For a spiral rosette I made up a spiral template which fits over a central 1/8 in pin, which I use to register all of my rosette cutting. With this template I am only interested in the outer spiral.
To make the cut against this outer spiral I also made up a small base which fits the Stewart-Macdonald Dremmel router base. This base has glued into it a bit of 3/16 brass tubing which sticks below the base and rides in the channel of the spiral template.
Using a fine down-cut bit, and pressing the dremmel and router base against the spiral one cuts a thin spiral outline.
Then I switch router bases to the one I use for circular rosette cutting. This base has a series of holes that fit over the 1/8″ registration pin. Between successive holes the circle which is cut changes by 1/32 of an inch.
Using this I cut a circle which just meets the tip of the spiral and contine this circle around. The sound hole will be centered in this circle, cut with the same router base, just moving to lower order holes. As I am cutting the spiral rosette, by moving to successive holes I clean out the whole spiral channel
Now all that remains is to do the pearl work. Since I have the drawing of the spiral template in Corel Draw I can us that to print the pattern to cut the pearl.