Sunday, August 29, 2010

Making an inlayed rosette, Part 1

I've started work on a new instrument this week, a midsized steel string. I intend to follow the construction closely with frequent blog updates!

Here I'll describe my process for making the traditional Spanish-style mosaic inlay used to decorate the soundhole perimeter on classic style guitars. I've scaled the size down a little to be more in keeping with the steel string aesthetic.

I credit this entire process to master luthier Eugene Clark, who's method was detailed wonderfully in the Journal of American Luthiers, issues 71 and 73.

My rosettes are constructed from strips of veneer (0.5 mm/.025" thick). Some of these I buy in sheets ready dyed, others I color myself using aniline stains cooked in a big pot on the stove, not unlike spaghetti, but even more al dente'.

I've devised some interesting jigs to cut the strips. In the end I came to the conclusion that by just making little pencil marks and going at it with a wooden straightedge and sharp knife, my eye quickly becomes adjusted to gauging the size. It's much quicker and accurate enough. They end up about 2mm wide, a convenient size to work with. Eventually they'll be scraped square in cross section.

Traditional steel string instruments often have designs made up of concentric lines- a quick and easily accomplished solution for the factory. Early Spanish luthiers often employed geometric or floral patterns. Eugene Clark associates the design process with weaving and textile arts. To me, it feels more akin to the Italian art of Millefiori glass.

The pattern options are boundless! As individual craftspeople we have the opportunity to be a little more personal with the motif. I'm using this little character here, a skull figure that in this format has a definite old-school Space Invaders aspect. (Yes, I know there's no nasal hole! Don't ask me why - that's just the way it is!)

I plotted the design out on graph paper and transcribed the squares of color into a sequence to assemble the lines into individual rows.

Having a big sink nearby is important. It's a messy business. The top of the washing machine becomes a ready made workbench! I'll be using yellow carpenter's glue as an adhesive. The laminate workboard has a piece of hardboard screwed down to make a straight fence to press against. It's hard to see, but the edge has been covered with clear packing tape to provide waterproofing.

I'm not stingy with the glue. It's important to get every strip thoroughly saturated. The glue has been thinned with a small quantity of water to extend the working time. I cover five or six strips at once and line them up. They are then squeezed lightly between thumb and fingers and excess glue wiped off before adding more lines to complete one row of the pattern.

A couple of thin Plexiglas sheets provide a light, even pressure to hold the now assembled row straight against the fence. The surface of the workboard and fence has been slightly dampened to prevent the row from sticking too firmly, but also to provide a little surface tension to hold the plexiglas down flat on the board. The five minute interval required will allow the glue to seize up before I run a pallette knife around the row to free it. The next row goes in, and the previous row gets set aside to dry.

The rows have now been readied. These are about 12", (300mm) long. This length is easy to work with and cuts down on the incidence of breakage during the thicknessing process.

Rough thicknessing proceeds with a block plane. I hold the rear end of the row in my hand - there's no safe means of butting the row against a stop block as it's too thin and would bend or break.

Planing yields a big fuzzy ball of gore.

This is an old #90 Stanley shoulder plane in bullnose con-figuration clamped to a maple block at close to 90 degrees. The rows are slipped between the blade and fence at a point about 1/3rd their length and pulled (carefully) toward me. I then reverse the strip to scrape the other end. As I started with veneer 0.025" thick, that should be the final thickness of these strips to ensure the ends will as tiny squares in the finished product. Work progresses by advancing the blade in very small increments, flipping and rotating occasionally to ensure even stock removal, and eventually things get done. It takes some time, but it's a good opportunity to reacquaint ones'self with an old album, in this case it was Muddy Waters' "More real Folk Blues".

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