A Glimpse into Acoustic Guitar Building

A successful businessman keeps “in tune” with his passion for tools and woodworking by tackling the intricacies of guitar design and construction.

By Shiraz Balolia

The name “luthier” refers to a person who builds stringed musical instruments and is derived from the French word “luth.” This article will cover just some of the intricacies of building a fine steelstring guitar.

Lutherie, particularly acoustic guitar building, is one of the most challenging forms of woodworking and stretches the abilities of even an accomplished craftsman. It requires one to think carefully before acting and, like a game of chess, forces you to calculate the results of your actions several moves ahead. Unlike most woodworking projects, you need to think in thousandths of an inch, and with wood, that is a daunting task.

The most important component of an acoustic guitar is one we can all relate to, wood. Certain woods are very beautiful to look at, but are not desirable acoustically. Others are fairly bland, but have dynamic tonal qualities. The guitar body usually has two different species of wood – one that makes the back and sides and another that makes the top, or soundboard. Since the body of the acoustic guitar is around 16 inches at its widest point, the back and soundboard are almost always made up of two pieces that are bookmatched and joined together. Usually the backs are finished at 0.115-inch thick, the soundboard at 0.112-inch and the sides at 0.080- to 0.090-inch thick.

Brazilian rosewood, which is listed as an endangered species, has the reputation of being the “king” of backs and sides due to its tonal qualities. The most widely used wood now is Brazilian’s cousin, Indian rosewood, which experts have found to be the “second best” in its qualities as an instrument wood. Other woods that are very good for backs and sides include mahogany, maple (usually curly or quilted), bubinga, Macassar ebony and koa. The best woods are usually quartersawn with nice, tight growth lines.

Achieving the proper sound

Soundboards have to be super-light, super-strong and be able to vibrate with the sound produced when the strings are plucked. Spruce easily is the winner here, although cedar has phenomenal sound and is most often used on classical guitars. For clarification, nylon string guitars that have a slotted peghead (where you tighten the strings) are known as classical guitars. Steelstring guitars are self-explanatory, and most of the discussion in this article is based on steelstring guitar construction.

Going back to the spruce, there are numerous types of spruces available. Sitka spruce that grows in the Pacific northwest and Alaska is the most commonly used spruce, although the European or German spruce has the reputation of being richer in tone and creamier/whiter in color. Englemann spruce that usually comes from Canada is also widely used.

However, the very best soundboards are made of Adirondack red spruce that is currently protected by U.S. Forest Rangers. There are several private stands of these trees, and it is available in limited quantities. I was fortunate to get three top-grade soundboards of true Adirondack spruce from a very good acquaintance, who cut a 260-year-old tree from his private stand.

Previously we talked about working in thousandths of an inch, and every woodworker knows how wood “moves.” That is precisely why controlled humidity in a shop environment is important. For guitar building, the ideal humidity should be between 40 percent to 50 percent. I try to keep my shop around 45 percent. If the humidity is fairly constant and controlled, you have a better chance at retaining close tolerances with the parts you are putting together on your instrument. Most guitar makers let the wood season and acclimate to their shops before working with it.

     
 
Bracing is being glued to a soundboard using a radiused dish as a form on the bottom. Perfect pressure and total control is achieved with an ancient method that uses flexible sticks (in this case, fiberglass rods).  
     

Sound bounces for a longer time when it comes in contact with a curved surface as opposed to a flat surface, and most acoustic guitars have slight curves on the backs and sides. Steelstring guitars have a larger radius on the backs than on the tops. I make mine with a 15-foot radius on the backs and a 25-foot radius on the soundboards.

Braces are glued to the insides of the backs and tops and, quite often, the design of the bracing on the tops can make the difference between a poor-sounding instrument and a great-sounding instrument. Bracing has to be strong, yet allow the soundboard to vibrate appropriately. Many of the larger factories have slightly different bracing patterns that give their instruments a “trademarked” sound. Bracing is a balancing act in controlling weight and tonal quality while making the instrument structurally sound.

Special jigs make all the difference

Critical to lutherie is the need for special jigs that speed up the process of repetitive functions. Shown below are pictures of a side bending jig that allows you to use the same jig for different shapes of guitar bodies simply by changing the inner form. A rubber heating pad or “blanket” as it is known, is sandwiched between two stainless steel sheets that bend with the wood.

Another very important jig is what is known as the “go-bar” jig. This is an ancient method of using flexible sticks (or fiberglass rods, in this case) to put localized pressure on uneven and hard-to-reach areas that are commonly encountered on musical instruments. These jigs are especially critical for gluing bracing to the curved backs and tops.

Radiusing the fretboard

The fretboard is the thin piece of wood that forms a layer on top of the neck of a guitar. Normally fretboards are made of ebony, Indian or Brazilian rosewoods or, in some cases, maple. The prerequisite for a fretboard is that it needs to be very hard, since it will get a lot of wear and tear. Almost all steelstring and electric guitar fretboards are radiused, with the most common radius being 12 inches. If a player likes bending his notes or plays the blues a lot, there will be a sharper radius on the fretboard.

Fretboard thicknesses vary a bit, but are normally 5/16 inch at the top (near the peghead) and 1/4 inch at the bottom (near the soundhole). The jig shown below is mounted on an edge sander and a vacuum mold holds the fretboard blank while the arm is moved back and forth. Starting with a 5/16-inch-thick all-around fretboard, I can normally put in the radius and thin the bottom end all in one process taking no more than three minutes.

Take the worry out of neck shaping

When luthiers first start to build a guitar, they cringe at the thought of the work involved in the shaping of the neck. Maintaining the exact shape and dimensions of the neck back contour can be challenging, but not if you use jigs. I built a couple of simple jigs that I use on my shaper (see photos at right) which does the majority of the neck shaping work. Beyond that, you are left simply to round off the backs either manually, using more jigs, or machining the part on a CNC router, if one is available.

Finishing

Finally, it is time to finish the guitar. Most steelstring guitars are sprayed with lacquer. In my case, I spray eight coats of nitrocellulose lacquer and buff it out for a gleaming wet look. I usually start by spraying two coats of sealer, sand to 320 grit, and go up to 1,000 grit between coats of lacquer. After the final coat has been sprayed and allowed to cure for about ten days, I finally sand up to 2,000 grit and then buff out with Menzerna buffing compound.

     
 
Abalone, Mother of Pearl and ebony inlays were used in the back of this guitar body.  
     

The neck and body are finished separately and then fitted together at the very end. Once the neck is on, critical measurements are taken from the 12th fret for bridge location. Once the bridge is glued on the body, strings are installed, action adjusted and a big hug and a wet, slurpy kiss can be given to your new baby.

Shiraz Balolia is the founder and president of Grizzly Industrial Inc. He is an avid woodworker as well as a metalworker and has an extensive workshop, including a machine shop, in his home. He builds guitars as a hobby.


Adding a Personal Touch

No project is complete unless it has your personal mark on it. Embellishing an instrument depends entirely on taste and skill. It can range from a simple name or initials on the peghead to a more intense and difficult vine on the fretboard. Whatever your preference, the inlay pieces and their cavities must be a tight fit or the intended beauty will be lost.

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