These notes provide some insight into the processes that go towards the building of Siragusa Guitars’ instruments.
Instrument Building Approach
My approach to guitar building involves a combination of traditional handskill construction methods, traditional machining processes, computer-based machining operations and the employment of principles of physics. My design process usually begins with ideas that I input directly into a CAD program and then develop into a 3D model. After refinement, the 3D model is broken down into individual components where some of these are further developed for CNC machining. The final shaping, fitting and finishing is still done with traditional woodworking handtools, specialised lutherie tools and fine-tuning measuring instruments so that I have control over how each instrument will: 1) feel in the hands of the player; 2) produce tone; 3) maintain structural integrity; and, 4) will look aesthetically. Every piece of wood, even from the same species (and even the same tree) will have different characteristics – some wood will be more dry and brittle, some more oily, some have complex grain patterns, etc. – and, hence, can only be worked by hand to produce an instrument of high quality.
The building Process
The building process involves the combination of traditional machining, computerised machining and specialised hand tool work. There are some misconceptions about the use of CNC machines for guitar building. They do not only just produce guitars for the mass market. For me, my CNC machine is just another one of several machines (e.g., bandsaw, jointer, thicknesser, etc.) that I have in my workshop to help me transform larger pieces of wood into smaller pieces that get further shaped and refined by hand (including tap tuning) to become parts of a musical instrument. For example, the neck on my Mistretta guitars are the same shape for each guitar in this model range. The combined neck, headstock and heel are ‘roughed out’ using my CNC machine – usually leaving a few millimeters for the final shaping and fitting to the rest of the instrument. This helps with quickly roughing out the bulk of the material to a consistent shape that I can then refine for each individual guitar. Refining involves precise hand work for the fitting and shaping of components such as braces/tonebars, bindings and purflins, internal linings, rosettes, inlays, frets, bone nuts and saddles, and sanding and finishing.
The physics
During the construction of Siragusa Guitars instruments, there are processes carried out to assist with achieving desirable and consistent tones from the instrument’s components. The overall sound of a stringed instrument is a result of its individual components (i.e, soundboard, braces, tonebars, backplate, etc.) working as a whole; this is referred to as a ‘coupled system’. Each piece of wood from the same species will be different and, hence, each piece requires individual treatment in order to achieve consistent tone. To compensate with the differences in wood, each soundboard and back plate are “tuned” using tap tuning techniques (as published in Roger Siminoff’s 2006 book, The Art of Tap Tuning). In essence, Siminoff describes soundboard tap tuning as working on the principle that there is a balance between stiffness of the soundboard and the bridge’s load exerted on to the soundboard, which affects the instrument’s amplitude and tonal qualities.
The stiffer the soundboard, the higher the frequencies it produces. To lower the frequency, the stiffness is reduced by removing material from components such as the tonebars and braces, as well as reducing the thickness of the soundboard. The backplate stiffness can also be reduced by removing material from its braces. Measuring the frequency changes, as a result of removing material from a component, is done by the using a mechanical strobe tuner, which gives accurate readings of the initial attack produced by tapping the component with a tap tuning hammer. Material is removed until the component produces the desired frequency (a note of the concert pitch A440) when tapped.
For acoustic guitars that have a saddle seated in a fixed bridge on the soundboard, the bridge’s load influences amplitude and tone, which is largely controlled by the string break angle over the saddle. The load is increased by increasing the height of the top of saddle above the soundboard. A light load, where the string passes over the saddle with little break angle, will result in reduced amplitude and possibly undesirable tone; a great load, where an excessive break angle occurs, impedes the soundboard to vibrate freely and may possibly result in unwanted component distortions or failure. While there is an ideal range for saddle height to achieve a suitable load leading towards desired amplitude and tone, the height is also affected by factors such as the neck angle and the playing action required.
The finishing
The purpose of the finish is to protect the instrument from handling while not interfering with the tone. Hence, the finish must be resilient enough to resist minor impacts, environmental changes and player’s sweat, and so on, but not too hard or too thick to restrict the movement of components such as the soundboard. The finishing schedule of our instruments is typically: 1) pore filling with a suitable filler product, 2) sealer coats with either amber or blond shellac, 3) finishing coats with nitrocellulose lacquer, and 4) a final protective coat with a carnauba-based wax.
Intonation
An instrument with perfect intonation will have perfect pitch accuracy at every note. Creating a stringed, fretted instrument with perfect intonation at every note is very challenging. A string length will change slightly when the string is fretted because the string will stretch as it is pressed towards the fret. Fretting an instrument with a high action will cause the string to stretch more than an instrument with a low action. Pressing hard on the string will also cause it to stretch a little further than pressing lightly.
More to come…
