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Fundamentally, two types of guitar neck construction exist; single and two-piece. In a single-piece neck the headstock is cut into the same piece of timber as that of the rest of the neck. In a two-piece neck, a separate headstock part is joined onto the longer part comprising the greater length of the neck using a scarfed joint. Origins Of The Term The term "scarfed joint" reaches back to traditional timber building and ship construction to denote a type of joint used to produce a long piece of timber where one single piece would not otherwise be possible. The joints themselves were often complex and varied, not glued and instead used a combination of friction, mechanical locking using wedges/pins, fasteners, gravity, etc. The development of strong adhesives beyond simple protein glues changed joinery and produced a whole new book to describe them. The term "scarfed joint" was appropriated and used to denote both the a lengthening strategy for joints glued at an acute angle for increasing mating surface area for glueing and as a method for improving the cosmetics of joints that would otherwise require weak and aesthetically poor butt joints, such as veneer wrapped around a cylinder. The term has again evolved in usage to describe how a two-piece neck is constructed for a guitar, derived solely from the increased mating surface areas they produce for glueing. In some ways it has become simplified over its original base meaning. So much so, the more descriptive and correct term "scarfed joint" has devolved into "scarf joint". Both are correct in the context of guitar neck construction through adoption (language and meaning evolves) however we'll stick to the more specific term "scarfed" for this article....we'll see why this is meaningful later.... Headstock Angles Most people will be familiar with the difference in headstock angle of a Gibson Les Paul versus that of a Fender Stratocaster. Whilst Fender-style designs have a headstock that lays in the same flat plane as the rest of the neck (zero headstock angle), headstocks of Les Paul-style headstocks typically fall away at an angle anything from a few degrees up to 20°. A few terms exist such as "angled headstock", "tiltback headstock" however they all represent the exact same thing; that the plane of the headstock is at an angle with respect to the rest of the neck. Angled headstocks offer benefits over flat headstocks, such as greater string pressure over the nut and the elimination of string trees. A side benefit is that they can also allow for easier access to the truss rod for adjustment. Why Use A Scarfed Joint? The main two reasons that scarfed joints are used is for the strength that they add to the finished workpiece and also one of economy. Many builders also incorporate aesthetic values to their scarfed joints as a secondary aspect, which in many ways also distracts from the true purpose of the joint being there in the first place. Wood Strengths/Weaknesses Wood is not an isotropic material; it is weaker parallel to the grain direction and splits along this easily. For necks whose length is more or less in line with the grain, (flat zero angle necks or very shallow angles) this is rarely a problem. The grain travels uninterrupted along the entire length from one end to the other. Headstocks angled against the direction of the grain build in an inherent weakness called short grain. This is simply the path of least resistance through the grain into and out of the wood, in this instance from the rear of the headstock a short distance through to the front. The greater the angle of the headstock, the shorter the grain distance and the weaker the headstock. Areas of short grain (red) in a single-piece angled headstock against normal grain direction (green) Short grain is one of the main reasons that Gibson guitars and basses are so prone to headstock breakage. Decades of adherence to their traditional building style maintains this weakness in spite of a simple solution having been around for far longer. The scarfed headstock joint. By glueing a second angled piece of wood to the first to produce a scarfed joint, short grain is virtually eliminated Economy It should be fairly apparent that a headstock angled against the plane of the timber increases the minimum dimensions that the timber is required to have for a single-piece neck, increasing the waste factor. Several strategies are possible for turning this into a more economical venture by employing a simple scarfed joint. The following diagram shows how shorter material can be used economically by recovering material wastage underneath the neck and using it as a scarfed headstock: Volutes In guitar terminology, a volute often refers to a strengthened area behind the union of the neck shaft and the headstock. These are useful for a number of reasons, not all of them related to scarfed joints. In this context however, they can be useful to lengthen grain when scarfing on a thicker headstock component that would otherwise invite short grain under the first two frets. Volutes also offer cosmetic options for hiding the join line; same as how a headplate can be added to the top of the headstock, a bent "backstrap" can be added to the rear face. A thicker scarfed headstock can add short grain from under the headstock The addition of a volute lengthens the area of short grain, adding vital strength Types Of Scarfed Joint As touched on earlier, the term "scarf joint" is less meaningful than "scarfed" since we're really discussing the idea of two-piece construction over single piece rather than any specific type of joint. There's no language police here, and both terms are just as correct through widespread usage and basic adoption. It is however useful to consider that there's lots of ways to achieve this end. The most common type of scarfed joint is that shown above; an acute face milled into the end of the neck, and a second flat piece of wood glued on. Several common methods exist to create a scarfed joint, however they all have two common aspects; they increase the mating surface areas of the two parts to ensure a strong glue bond whilst eliminating as much short grain as possible. The two most common types of scarfed neck joint; over and under the neck Notable exceptions to the common approaches on scarfing a headstock joint are the V-joint employed by Martin and many classical guitar makers, however this is seldom found on electric guitars or steel-strung acoustics. Cosmetically, this style of joint can be accentuated into a "dart" or even a diamond-shaped volute. Making a V-joint - https://www.youtube.com/watch?v=KocJHchKVZQ ....or the far more weird finger joint as employed by industrious inventor Bob Taylor: It might look strange, however as well-engineered as joints go this is near perfect in all but cosmetics In Closing Scarfed joints are an important building technique to increase the reliability and durability of guitar necks with angled headstocks, plus afford us opportunity to use raw materials more responsibly. However the joinery is approached, a well-planned and executed scarfed headstock produce an end product that can be both beautiful and superior to those made from a single piece of timber. They simply need to be applied to the problems that they are intended to be solving. Over in the tutorials section, we'll look at the different techniques used to produce basic scarfed joints plus jigs to simplify the various processes....
Hola! I originally introduced the idea of a compound scarfing jig waaaay back in something like 2007-2008. A few people around ProjectGuitar.com have successfully used the idea, and a few people around the interwebs have taken it on also....some clearly took it directly (including images and zero credit) however convergent evolution means it would surface of itself at some point anyway. It's all cool. Rising tides floating all boats and that. The idea was based off the established idea of a router scarfing jig, but improved to allow for twisted headstocks and even string pull for multiscales that do not have a nut perpendicular to the centreline. Normally the treble side of a multiscale is pulled backwards, causing the headstock to "twist" clockwise as you sight towards it down the fingerboard. The higher the difference between the two outer scales, the larger the twist. This creates problems for necks with tilted headstocks as the scarf needs to incorporate a new compound tiltback angle. Thankfully, there is a simple solution to this which isn't much more difficult than the standard router scarfing jig. Firstly, let's look at the standard router scarfing jig: At their most basic, they consist of a box bounded by two guiding rails. On top of this rides a router with a wide sled which ensures it maintains contact over both rails. The neck and usually the piece being scarfed are cut at the same time. Depending on the final orientation of the scarf, one piece has the glue joint surface cut whilst the other has a facing surface finished: Pretty standard fare so far. To make a compound angle, the sleds are simply offset from each other. Rather than riding on the faces of the sidewalls the sled now runs on the edges; the inner wall on the furthest forward and the outer wall of the furthest back. The correct offset corresponds to a line drawn from each contact point on a flat plane: When glued up, both halves produce the expected compound scarf.