graduation and strutting

The process of adjusting the thickness of a guitar top to its finished thickness is called graduation and the process of reinforcing the top with thin pieces (or struts) of wood is called strutting. Both of these processes have a very important influence on the sound of the finished guitar. There are many different philosophies and methods of graduation and strutting but a detailed examination of the work of the great luthiers of the last two centuries shows that they all adopted a set of common practices, with some variations. These practices are known today as the Spanish method of classical guitar construction, a method which has been adopted widely throughout the world. Other methods exist, and the interested student is encouraged to explore some of the contemporary developments in double top design after first obtaining a good understanding of traditional methods.

All graduation and strutting takes place on the inside of the top until the new guitar is assembled. Then, before the guitar is french polished, I will string it and make fine adjustments to the belly and edge thickness. I'll also work through the soundhole with small sanding blocks to perform fine adjustment of the struts. This technique allows me to hear the effect of final adjustments while I make them, and significant changes can often be obtained with slight adjustments in different areas.

The top of a modern classical guitar is arched, a development attributed to the Spanish luthier known as the father of the modern classical guitar, Antonio Torres (1817-1892) and his contemporaries.

In the traditional Spanish method, a top is constructed on a wood workboard called a solera. The solara is concave in the area from the bottom cross brace to the end block. When struts are glued to the soundboard on the solara, they cause it to assume and hold an arch similiar to this concave area. The arch allows a thin, lightweight and responsive top to be constructed with the strength necessary to resist the pull of the guitar strings. The precise shape of this arch is one important factor in the sound and sustain of a classical guitar. Here is a picture of the top of No. 28 on the solera showing one of the strut patterns I use.

After I inlayed the rosette, I reduced the top to a uniform thickness of approximately 2.5 mm. Great care must be taken to protect the front during this process because any small chips of wood will leave a mark on the top. Handle cedar especially carefully, and keep a good bench brush nearby.

I then further reduced the top to 2.1 - 2.3mm in the area between the bridge and the end block and around the edges of the lower bout, depending on a number of factors. I have found that the best tool for initial graduation of a top is a flat bottomed toothing plane or a short section of a fine razor saw blade held by hand and dragged as you would a toothing plane blade across the surface of the top. A flat hard sanding block or two completes the requisite toolkit. These can be made by the luthier from offcuts of wood and are renewed as they wear. I keep a couple around, both approximately 60mm x 120mm with 80 grit paper on one side and 150 on the other. Other useful tools include a small violin maker's plane for shaping struts and cross braces, with both regular and toothed blades, and a set of strut sanding blocks. I've used flamed maple for the cross braces on the Indian rosewood back for this guitar, and a toothed blade in the plane is essential when shaping the tops of the braces. Strut sanding blocks are normally made by the luthier and consist of finger sized sanding blocks with profiles which match the outside profile of the top struts and cross braces. I have a box of a half-dozen I've accumulated over time, and I occassionally make more when necessary.

During the process of top graduation, experienced builders will frequently stop, test the flexibility of the top with the fingers, bow in the direction of Cordoba, Munich, Madrid, Paris or New York, take a break, light a candle, reflect on past experiments in graduation and their results, hold the top between two fingers, tapping it in the bridge area with the fingers while listening for particular tap tones, take another break for a glass or two of good red wine, eat some tapas, perhaps ignore the new top for a couple of days, return, meditate on the relationship of intuition to outcome, engage in various practices which an external observer might find incongruous, repeat the processes and rituals described above several times, then finally and for no apparent reason call the task finished, and proceed with the guitar construction.

This process might take a day, several days or a week. This one took several days, on and off. It is during this stage of guitar construction that the nature and personality of a fine guitar is acquired. It is a process entirely dependent on intuition, experience, sensitivity to material, imagination and luck. This is where the Art of musical instrument making is found and where the soul of a guitar is born.