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Things to Know About Guitar Wood
My initial attraction to woodworking was the wood. Its many colors, grain patterns, and texture make it a wonderfully interesting medium. Having worked as a cabinetmaker, and a designer and builder of studio furniture, I had a wide experience working with different woods, but it wasn't until I studied woodworking with James Krenov that I really began to understand the material. Jim taught us all how to extract desired graphics from the wood by cutting it a certain way. He also stressed that wood has an assortment of physical properties that have a personal effect on both the maker and the client He made me understand how some woods are suited for some applications while others are not because of the physical characteristics. He would always encourage us to pay attention to texture, color, and the feel of the wood because we relate to almost everything in this way.
The guitar's shape is quite human, almost sensual. The shape is interesting all by itself. For me wood used on the larger parts of the instrument work better when the grain is straight and calm, not demanding attention. Wild and highly figured wood on the main parts of the instrument compete for attention with the shape and can be distracting. Therefore the highly figured wood in my opinion work better on smaller parts such as the headpiece and rosette where their function is purely decorative but undemanding.
I encourage you to expand your knowledge of the different types of wood. Perhaps you can try making something else, maybe something small and easy just to experience the wood and the effects it has on you and your design. Begin to build a personal catalog of wood and how it works for you. If you do you will vastly improve all your projects including guitar building.
Guitar building adds another characteristic we must pay attention to and that is the addition of sound. The wood is the reason the instrument sounds the way it does. The acoustic properties of wood vary from species to species and once again you will need to amass your own personal database with these characteristics. There are sections on the web site that provide information on back and sides wood, sound board wood, and neck wood that explain how these woods effect the sound of the instrument for me. Of course you will have to develop your own vocabulary for this.
Guitar Wood and Moisture Content
When a tree is first cut down, the cells are full of water. Once the wood is milled into usable lumber, its moisture content begins to decline, and will continue to decline until equilibrium is reached with the moisture in the air around it. The term for this is Equilibrium Moisture Content (EMC). Without the help of a kiln the rule of thumb for air drying wood is one year for every inch of thickness. Kiln drying speeds the process considerably but may alter the color in some wood types.
Once the wood has reached equilibrium, the moisture exchange with the environment does not stop. As the humidity rises, the wood takes on moisture and grows in dimension. As the air becomes drier, the wood gives up moisture to keep up with its surroundings and shrinks in dimension. This can be witnessed in the shop by placing a freshly milled piece of thin wood flat on the workbench. You will notice the edges of the wood will curl up, making the wood appear concave; or the piece will bulge up in the middle, creating a domed look. The first scenario indicates that the air is dryer than the wood and the top surface of the wood is giving up moisture and shrinking. The second scenario indicates the air contains more moisture than the wood and the top surface of the wood is taking on moisture and swelling. In both cases the dimensions are changing. The introduction of moisture can also cause the wood to warp and twist.
Always be sure to inquire when purchasing guitar wood if it has been dried or not, and whether it was dried in a kiln or air dried. If the wood has been air dried, you will also want to know how long it has been drying. Wood that has not been dried fully will need to sit until equilibrium is reached. Wood tends to give up moisture much faster through the end grain than the face grain, and that is why you will sometimes notice end checks or cracks at the ends of boards. To avoid this, coat the ends of the wood with paraffin wax or even glue, in a pinch, to retard the loss of moisture through the end grain. Also, all wood, when not in use, should be stickered. Stickering is placing a small piece of wood under each end of a board, 1/8 inch of height will work just fine, so that air can freely circulate around the entire piece (see page header).