Making a Diamond-and-Ball Rosette
by John Osthoff
Here is the Description of the process that I used to create the Lozenge-and-ball Rosette. I got the idea out of Irvin Sloan's Steel-String Guitar Construction book. According to Sloan, the pattern was taken from Stradivarius for the ivory and paste purfling of the Rode Violin (1722). Al Carruth also did one of these rosettes. His influence was also from Stradivarius but came from his 1688 guitar that's in the 'Shrine to Music Museum.' Regardless of the influence, each luthier has the opportunity to add their own personal flair to the design as well as using construction techniques that best suit their own needs.
I have used a drill press mounted fly-cutter for rosette channels in the past but I did these channels with a Dremel tool and down-cut router bit. I made the router attachment out of some smoked plexi that I had. They sell something like that in Stew-Mac but it was easy to make. The Dremel router base came from Stew Mac. I used a piece of tape as a reference mark to tell how much the fixture was moved when making adjustments.
I routed out two channels to accept the purflings. I used (3) WB .020' strips sandwiched between some .040' black strips. Notice the piece of wood with the purfling strips going through it. It is the purfling organizer idea I got from the 'the Fret.' Thank you to whoever posted that and gave me that idea! It is just a piece of small wood with some holes drilled in it to keep the purflings in order. It really works great.
Al did his routing and purfling strips a little differently. He routs the whole channel at once. He then makes a 'keeper' ring cut from plexi. Cut a gap in the ring in case you don't get the diameter of the rout just right, and use it like 'no-stick strip' as a place-holder for the fill as you glue in the rings. He likes to pre-laminate rings around a plexiglass plug. Clamp them in place with a split plexi ring and a hose clamp to make them come out uniforn in thickness. You can make all sorts of herringbone and other patterned stuff that way and just 'slap' it in.
Next I laid out for the Mother of Pearl (MOP) dots. I bought them after making a few. The price out-weighs the effort of making them. I used 3mm (about 1/8 inch) Dots. The diamonds were all cut out from .050' thick MOP. I printed an outline of the diamond on address labels and stuck them to the pearl. I used a cut-off wheel in my Dremel to do most of the cutting. Al made a little miter box for cutting pearl diamonds out of a strip. A narrow bladed X-Acto saw works fine, and lasts a surprisingly long time. (I will definitely do that next time.) Al suggests that you can piece together some pretty cool snowflakes from 60 degree diamonds.
Next I routed the channel for the MOP. Try to get the depth pretty close to the thickness of the MOP. I glued all the dots in first and then did the diamonds. I used cyanoacrylic to hold down the dots and diamonds. Then it came time to fill around the MOP. I used black epoxy. Sloan's book said to grind up refined charcoal and mix it with white glue. I think you could use black furniture powder too. Fill it and sand it down. It took about 3 times to get the epoxy level. But Al offers some word of caution. 'The biggest problem I had on mine was the use of black-dyed veneer for the purfling lines. I used 'West System' epoxy for the fill, and the color leached out of the purfling lines and into the end grain of the top! I did manage to sand it back enough to look good, but.... Be sure to check all of your materials for compatibility first folks!'
That's it. That is how I did that rosette. I am really happy with the outcome. It took some time but it was fun. Thank You, Al for your comments and encouragement. Visit his site Al Carruth Luthier
Once again the finished product.