It All Begins with the Wood by Bob Gleason Pegasus Guitars and Ukuleles
The subject of wood is one of the most contentious issues in luthiery. It is in fact a fairly simple one. Aside from the artistic and emotional approaches, I think wood selection is straight forward. In general we are looking for quartersawn wood with little or no imperfections such as knots or stains, and as little run-out as possible. Quartersawn refers to grain that runs more or less perpendicular to the wide flat surfaces of the board, as viewed from the end of the board. Figure 1 shows a log section and how the grain looks from the end of the board. Figure 2 illustrates grain run-out. This is often called shortgrain and is structurally very weak. The grain lines should run parallel to the wide surfaces of the board. This is fairly easy to see in lumber if you look at the side of the board.
Many luthiers measure the stiffness and density of the wood they use with the aid of mechanical devices. The most common method of doing this is to use weights placed on similarly dimensioned wood. The amount of deflection under the weight is measured with a dial indicator.
I encourage beginning builders to not get too hung up on using perfect wood and to understand that the wood they use does not need to meet the highest classical luthiery standards. Small tight knots and color imperfections are not serious problems.
Although we generally quartersaw all structural wood, i.e. tops, sides, backs, bracing, there are instances when flatsawing is preferred. Some of the woods used for ornamental bindings such as purpleheart and Bolivian rosewood, are very brittle and bend much easier when flatsawn. Other woods, such as pheasant wood, must be flatsawn to show their true beauty. Sometimes a piece of curly koa will be stunning when sawed off the quarter and thats fine for bindings and headcaps.
Woods used in non-structural ways on the instrument can be sawed to best exhibit the desired wood characteristics. And some woods, such as Brazilian rosewood, are considered so hard and stable that they are used structurally no matter how they are sawed.
In musical instrument making there really is no consensus as to what wood produces "THE" sound. In fact, the wood selection plays a fairly insignificant role until building skills are at the advanced level. Through most of my luthiery career I have sold small amounts of wood to finance my own "wood habit". Invariably the inquiries I receive are for the highest quality of wood even though the builder often has very little experience. If you are at the early stages of building, dont spend your money on "KILLER" wood. Buy better tools and learn how to use them.
As instrument makers in Hawaii, our main source of locally available wood is wood from the koa tree (Koa acacia). Aesthetically there is hardly a wood in the world that matches it. As an instrument wood however, it leaves much to be desired. Koa is riddled with defects such as knots, wind shakes (cracks found throughout the wood), ingrown bark, weak grain lines, plenty of rot, and the dreaded hidden stains that become a visual nightmare on a finished instrument. Everyone seems to want the most highly figured examples of koa .In wood like this you rarely find true quartersawn wood and you always have significant run-out. This kind of koa is particularly bad for tops, often leading to distorted tops and bridge failure. That said, very curly wood is about all I ever use for ukes because of the demands placed on me by my customers. At times I find myself having to alter a design to ensure against the failure of a piece of wood, rather than to improve tonal qualities of an instrument. Having some knowledge of the characteristics of the cut of the wood will allow you to work with less than "perfect " wood.
The majority of ukulele top woods used in Hawaii are hardwoods such as koa, mango, milo, and mahogany. These woods are tonally and structurally quite different than the softwoods such as varieties of spruce, fir, redwood and cedar. The hardwoods lack the long fibrous cell structure of softwoods. As a result they are more prone to distortion under string tension and in time retain a permanent distortion even when the string tension is removed. Im sure youve all seen old ukes with what is called a collapsed belly, bellied top, or rotated bridge. These are all common names for various forms of top failure, which leave the top in a permanent state of distortion. Usually this rotates the bridge so that the saddle is no longer in the correct place and the string action is high, causing the intonation of the notes to be rather hard on the ears. Softwoods, though they can fail too, are less likely to develop this permanent distortion. If a problem does occur with a softwood top, and the value of the instrument warrants it, you may be able to rebrace it and return it to a playable state. Hardwood tops, generally, cannot be rebraced. Hardwood just wont flex back to a flat state. Tonally, softwood tops will usually provide a longer sustain of notes and a wider range of overtones preferable for a full rich chord sound. This is very desirable in guitars, however many ukulele people prefer the shorter crisp notes of hardwood. Possibly the uke becomes a little bit less of a true uke with a softwood top even though I like the basic sound better. Confusing, no! Simply stated, in attempting to make the uke sound better I am aware that, to me, there are some parameters to the "uke sound". The ideological approaches to luthiery are constantly changing. There are many ways to do almost everything in the building process and no ones methods are the absolute answer. It can, at times be a very stodgy endeavor, and the rules can get a little too lofty. If you cant figure out how something is done, come up with an idea and just make it work. Just relax and have fun! Next time Ill discuss some of the interesting tooling involved in uke making.
Aloha, Bob Gleason
Pegasus Guitars and Ukuleles