From: Charles Tauber Subject: BASIC GUITAR SET-UP Parts 1,2, & 3 Date: Thu, 16 May 1996 11:37:26 -0700 Reposted by popular demand. Feel free to distribute this to anyone who is interested, but do not publish it for profit without my prior permission. Charles Tauber, Luthier 1996 tauberc@candu.aecl.ca *********************************************************************** Basic Guitar Set-up 101 1. INTRODUCTION Many of the techniques and much of the theory which I have outlined below is based upon what I have learned from those generous enough to share with me what they knew. The techniques I have described are only one way of doing things; there is no one right method, though some methods are quicker and easier than others. What is more important than rigidly adhering to a set of techniques is to understand the theory behind the techniques. Understanding the theory provides you with a basis for separating the facts in guitar set-up from the abundant mythology. Once you understand what you are trying to accomplish (the theory) you can adopt, or adapt, specific techniques for accomplishing each task. While the following discussion strictly applies to steel string acoustic guitars, the basic theory is the same for classical and electric guitars, as well as a wide variety of other fretted string instruments. 2. THE FOUR ADJUSTMENTS There are four, and only four, basic, universal adjustments that affect the playability of every guitar. These are as follows: adjusting the amount of relief (or "bow") in the neck using an adjustable truss rod; adjusting the string height at the saddle; adjusting the string height at the nut; and, adjusting the intonation. These four adjustments are what I refer to as "basic guitar set-up". In contrast to "repair" work, which is work that may need to be performed on a specific instrument in order to maximize the playability of that particular instrument, set-up work is a series of adjustments that need to be performed at least once on every guitar. Very few manufactures take adequate time to properly perform these adjustments. Even when manufacturers do, the set-up is very general and aimed at the "average" player, rather than the specific preferences of an individual player. 3. NECK RELIEF As a simplistic description of basic guitar mechanics, the guitar's body mechanically amplifies the vibration of the guitar's strings. For a guitar, the vibration of a string is initiated by first displacing the string from its rest position - the position it assumes while it is at rest and under tension - and then releasing it. The elasticity of the string, and the tension imposed upon the string, causes the string to overshoot its natural rest position until it reaches nearly the same displacement in the opposite direction. Due to a "loss" of energy with each overshoot, the amplitude of the string diminishes ("decays"). The general shape of the amplitude of the vibrating string is a shallow curve that begins at one end of the string, is a maximum at the string's mid-span, and ends at the other end of the string, with the amplitude diminishing over time (decay). Thus, there is no displacement of the string at the nut or saddle, and there is a maximum displacement at the 12th fret. To accommodate the amplitude of the vibrating string, there are two options: either raise the height of the strings (the "action") sufficiently that the bottom of the vibrating strings do not touch the tops of the frets, or make the top of successive frets assume the shape of the vibrating string. The string height can be minimized by doing the latter, which reduces the distance that the strings must be depressed for fretting. This, in turn, makes the guitar easier to play. Practically, the way in which the tops of successive frets are made to conform to the amplitude of the vibrating strings is to introduce a slight curvature to the neck. This curvature, which is a slight upwards concavity, is usually referred to as neck "relief". The amount of neck relief required depends upon several factors, including string height, and, of course, string amplitude. If the string height is sufficiently great, no neck relief is required; the vibrating strings will clear the tops of the frets regardless. This, however, reduces the ease with which the strings can be depressed. The amplitude of a vibrating string depends upon several factors including string tension, string material and the initial displacement of the string (ie. how hard the string is struck). The same set of strings when tuned down (ie. lowered tension) will have a greater amplitude than when at pitch. Similarly, a lower tension string, when tuned to pitch, will have a greater vibrating amplitude than a higher tension string tuned to the same pitch. Any string type will have a greater amplitude if struck harder (ie. given a greater initial displacement). Thus, there is no one correct amount of neck relief; the amount depends upon the preferences of the player, the type and tension of strings used and the type of "attack" used by the player. As a general guideline, approximately 1/64" or 1/32" of relief is typical. This is generally measured at a fret that is at the mid-span of the neck (typically the 7th fret) and is the distance from the top of the fret to the bottom of a string when the string is fretted at the first fret and at a fret where the neck joins the guitar body, typically the 14th fret. By simultaneously depressing a fully- tensioned string against the first and 14th fret, the string forms a straight edge spanning the first and 14th frets. Alternatively, a metal straight-edge can be laid along the fingerboard (on top of the frets) and the distance measured from the top of the 7th fret to the bottom of the straight edge. For a guitar equipped with an adjustable truss rod, adjusting the amount of neck bow is quite simple. While there are a number of adjustable truss rod designs, each shares the same basic principles of operation. Specifically, when a threaded nut is tightened on a threaded metal rod, the resulting tension in the rod alters the curvature of the neck in which the rod is embedded. Adjustment of the rod involves tightening or loosening the nut on the rod. Tightening the nut increases the tension in the rod, and consequently increases the amount which the rod counteracts the pull of the strings, thereby reducing the bow in the neck. The truss rod nut may be located at either end of the rod, at either the guitar's head or from inside the soundhole. At the guitar's head, the nut is often concealed under a small plastic or wooden plate, fastened with small screws. From the soundhole, the truss rod nut may be directly accessible through a hole in the cross brace, or may be located at the heel block, often accessible only by completely loosening the strings. To tighten or loosed the nut, you will require either an allan key or specialized socket wrench. (Standard allan keys are available at most hardware stores and specialized socket wrenches for this purpose are available for several dollars from luthier supply houses. Some manufacturers will include an appropriate wrench or key, particularly if they use a non-standard arrangement (eg. Larrivee).) Since the amount of string tension imposed upon the neck changes the curvature (bow) of the neck, whenever possible, the adjustment should be done while the guitar strings are at full tension. Where this is not possible (eg. some Fender electric guitars) it is an iterative process in which an adjustment is made with no string tension and then the measurement is taken after the strings are returned to full tension. This is repeated until the adjustment is correct. The required number of turns of the nut depends upon the amount of bow in the neck, the truss rod design and its installation. Regardless, the adjustment required rarely exceeds one or two full turns of the nut, and is often less than one. Usually, the truss rod nut is tightened by turning clockwise and loosened by turning counter-clockwise. In addition to this adjustment, it is often helpful to sight down the neck - from nut to soundhole - to observe the "trueness" of the fingerboard and identify any frets which may not be fully seated. A true fingerboard is one which has no bumps or hollows along its length (ie. is "flat"). For guitars with a joint between the neck and the body, it is a common fault to have a hump in the fingerboard just beyond the joint (ie. beyond the 14th fret on 14 fret-to-the-body guitars). The truer the fingerboard, the lower the string height can be set prior to getting string buzz. For guitars with either no adjustable truss rod, or that have sufficiently untrue fingerboards, the remedy is the same; remove the frets and dress (true) the fingerboard, followed by refretting. This procedure is "involved" and takes a skilled repairperson several hours to complete; adjusting the truss rod is a trivial adjustment that can be performed by the layperson in minutes. Hence, truing of the fingerboard will not be discussed in this article. It is very important to understand how changing the amount of bow in the neck affects the height of the strings relative to the tops of the frets. Ideally, from the point of view of ease of playing, the guitarist desires the fingerboard surface to be straight ("true") along its length and parallel (or nearly parallel) to the bottom of the guitar's strings. This would result in the strings maintaining a constant distance above the fingerboard along the fingerboard's entire length. This, in turn, would require a uniform effort to depress the strings and would provide the greatest ease of playing. If a curvature (bow) is introduced into the fingerboard (and neck), the strings will no longer be a uniform distance from the tops of the frets; some places along the string will be closer to the frets, while others will be farther away. If the curvature is concave upwards ("bowed"), the strings will be at their maximum height above the tops of the frets at the mid-span of the curve. Conversely, if the curvature is concave downwards ("back-bowed"), the strings will be at their minimum height above the tops of the frets at the mid-span of the curve. The characteristic symptoms of an overly bowed neck is a high action at the nut that becomes higher around the 7th fret. The characteristic symptoms of a back- bowed neck is fret buzz in the middle frets, around the 7th fret, and buzzing of the open strings against the first fret. Often, action exhibiting either of these characteristics is a result of an incorrect neck bow, and is "fixed" by adjusting the bow in the neck. It is important to note that the curvature of the neck affects the string height at both the nut and at the middle frets. It is, therefore, essential that the correct amount of neck bow be set prior to any adjustment of the string height at the nut or saddle. While the amount of bow affects the string height, it should never be used to specifically attempt to adjust the string height at either the nut or saddle. Adjusting the amount of neck bow is a separate adjustment that must be made prior to and independent of adjusting the string height at the nut and saddle. This cannot be over emphasized. First set the correct amount of bow in the neck, then, once it has been set, leave it at that setting and then adjust the string height, if necessary. 4. ADJUSTING THE STRING HEIGHT AT THE SADDLE The saddle height can be adjusted either before or after adjusting the string height at the nut. My preference is to adjust the string height at the saddle prior to adjusting the nut. Begin by measuring the distance from the top of the twelfth fret to the bottom of the sixth string while all of the guitar's strings are at full tension. I prefer to make this measurement by laying a 6 inch ruler, on edge, adjacent to and parallel to the string. The ruler is supported at one end at the twelfth fret and along its length by the adjacent frets, eleven, ten, nine, etc. The ruler I use is calibrated along its end - as well as along its length - and conveniently measures the distance from the top of the twelfth fret to the bottom of a string. Any similar method which measures the distance from the top of the twelfth fret to the bottom of the string can be used. Move the ruler adjacent to the fifth string and repeat the measurement. Repeat for each remaining string. Although the ideal string height will vary with the preferences of the player and the type and construction of the guitar, a typical "good" playing string height ("action") for a steel string acoustic guitar is about 3/32" at the sixth (bass E) string and about 5/64" at the first (treble E) string, as measured from the top of the twelfth fret to the bottom of the strings. The intermediate strings increase in string height gradually from the first to sixth strings. (Due to the type of music played, string materials from which the strings are manufactured, the string tensions used and type of guitar construction, classical guitars have a higher action, while many electric guitars have a lower action.) There are only three possibilities for the measured string height: the strings are at the desired height; the strings are higher than desired; or, the strings are lower than desired. In the first case, no adjustment is required. Each of the other two possibilities are discussed below. STRINGS TOO HIGH Using elementary geometry, it can be shown that a change in the string height at the twelfth fret requires about twice the amount of change at the saddle. For example, if a string height measured at the twelfth fret is 4/32", and the desired measurement is 3/32", the change in height at the saddle necessary to lower the string by 1/32" at the twelfth fret is about 2/32". Using the measurements taken, calculate the amount that each string needs to be lowered at the saddle. Measure the amount of saddle height that is projecting above the top surface of the bridge. The saddle must project at least 1/16" from the top of the bridge. This ensures that the strings exert a sufficient downward force on the saddle to prevent the strings from vibrating side-to-side on the top surface of the saddle. The side-to-side vibration often causes a string to rattle or be muted. If the 1/16" projection can not be maintained, a neck reset or shaving of the bridge may be necessary, both of which are jobs for either the professional repairperson or the skilled amateur. As an optional next step, you may wish to mark, using a pencil, the location along the saddle at which the strings cross the saddle. Completely loosen all of the strings and remove the saddle from the bridge, noting or marking which end of the saddle is at the first string and which end is at the sixth string. Although the saddle should only fit snugly, but not tightly, its removal can often be facilitated with a pair of pliers. (Saddles should never be glued in place within the bridge.) Most steel string acoustic guitars, as well as most electric and some classical guitars, have the top surface of the fingerboard domed or arched across its width. (Many players find a domed fingerboard easier and more comfortable to play.) To achieve the correct height of each string, the contour of the top (bearing) surface of the saddle will generally follow the same curvature as the surface of the fingerboard. However, to accommodate the slight increase in string height towards the bass strings, the saddle contour is less curved on the bass end of the saddle. From the top surface of the saddle, measure, and mark with a pencil, the calculated reduction in saddle height required for each string. A smooth curve can be drawn through the pencil marks on the face of the saddle. Clamp the saddle in a vise and remove the excess saddle height with a file, filing to the drawn line. When this step is correctly completed, the top (string bearing) surface of the saddle will be flat across its width and curved along its length. A string supported by a relatively large, flat bearing surface will tend to vibrate from side to side over the width of the supporting surface. This causes the string to vibrate against the supporting surface, resulting in either a buzzing sound or a muted string. To prevent this, the width of the top surface of the saddle must be reduced by chamfering the top edges of the saddle and rounding the remaining surface. Premature string breakage at the point of contact of the saddle is the result of rounding the saddle to too sharp a point (too small a radius). Creating too extreme a point also results in premature wear of the saddle; the strings quickly wear notches into the top of the saddle. Except in very certain circumstances, a guitar saddle should not be notched to accommodate the strings. A notched saddle is often the cause of poor intonation, buzzing and muted strings. In addition to the importance of correctly shaping the top of the saddle, it is also very important to accurately locate where each string is supported, or "breaks", across the width of the saddle. Accurately locating where each string breaks over the saddle and shaping of the top surface of the saddle are discussed below in the section entitled "Setting Intonation". Upon completing the shaping of the saddle, the saddle is returned to the bridge and the guitar retuned. STRINGS TOO LOW If the strings are too low, either a new, taller saddle can be made or the height of the existing saddle can be raised using shims. Making a new saddle is very similar to reducing the height of a too-tall saddle, as described above. Materials for shims can be plastic, wood, metal or paper, although I generally use wood veneers of maple or rosewood. Shims are cut to the width of the saddle, and are stacked underneath the saddle in the slot in the bridge. Placing shims beneath a saddle reduces the amount of the saddle that sits within the slot in the bridge. Effectively, the depth of the slot is reduced by the thickness of the shims, which places a practical limit on the amount that a saddle can be shimmed. Ideally, as a rule of thumb, a minimum of half of the total height of the saddle should be within the slot, with the remainder projecting above the top of the bridge. Provided that the saddle is the correct width for the slot, this ensures that the saddle is adequately supported and prevents the saddle from leaning under the pressure applied by the strings. Some guitars are fitted with a saddle design which readily allows the saddle height to be adjusted. Generally, these arrangements consist of a saddle suspended between two threaded posts, the height of which can be adjusted using a screw driver. While this arrangement makes it relatively easy to adjust the saddle height, it has a number of significant disadvantages, which explains why it is not more commonly used. 5. ADJUSTING THE STRING HEIGHT AT THE NUT Once the neck relief and the string height at the saddle have been correctly set, the string height at the nut can be adjusted, if necessary. At the nut, each string sits in a slot cut into the top surface of the nut. The purpose of the slots is to maintain the spacing of the guitar's strings and, in guitars without a "zero fret", to maintain the height of the strings at the nut. The first thing to determine is whether or not the string height at the nut requires adjustment. There are a number of ways of doing this, some qualitative and some quantitative. I prefer to use qualitative methods for determining if the string height at the nut requires adjustment. Quantitative methods, which I will not discuss in detail here, involve using feeler gages similar to the way in which they are used in setting the string slot depth, as described below. Qualitative methods, by definition, involve determining by feel, rather than measurement, whether or not the strings are too high or if they are too low. To begin with, I check that the string height at the nut is not too high. The criteria used to determine if the string height at the nut is too high is that the effort required to fret any or all strings at the first fret should not be greater than the effort required to do so at any other fret. One test of this is to play a barre chord at the first fret and at, say, the seventh fret. If it requires more effort to apply the barre at the first fret, then the nut is too high. (Recall that since we have already adjusted the bow in the neck and the string height at the saddle, the string height beyond about the third fret should already be as low as you prefer it.) Another test is to compare the amount of effort required to depress a single string against the first fret with the amount of effort necessary to depress the same string at the second fret while the string is still depressed at the first fret. This can be done by fretting a string at the first fret with the first finger of the left hand then, without lifting the first finger, depress the same string at the second fret with the second finger of the left hand. Compare the effort required in each case. If more effort is required to fret the first fret, the string height at the nut is too high. Next, it is necessary to ensure that the string height at the nut is not too low. The usual symptom of a nut being too low is that an unfretted string will vibrate against the first fret when the string is plucked. This results in a buzzing sound. The ideal string height at the nut is one in which if you pluck the open strings slightly harder than you would during normal playing, the open strings will just begin to vibrate against the first fret. The test that I perform to check that the strings are not too low is to strike each string quite firmly and observe at what point, if any, that string begins to buzz against the first fret. The string should just begin to buzz when plucked slightly harder than it would be during normal playing. If it won't buzz at all, the strings are probably higher than they need to be; if it buzzes at less than normal plucking force, the string height at the nut is too low. LOWERING THE STRING HEIGHT AT THE NUT If you found that the string height at the nut was too high, the following method can be used to reduce that height. The string height at the nut is usually measured adjacent to the nut as the vertical distance from the surface of the fingerboard to the bottom of the string. The ideal string height at the nut for each string is the minimum height above the fingerboard that just allows that vibrating string to clear the first fret. Typically, this is several thousandths of an inch greater than the height of the first fret. Any higher than this and the string is unnecessarily hard to depress; any lower and the string vibrates ("buzzes") against the first fret. Thus, the ideal string height at the nut depends upon the height of the first fret and the amplitude of the vibrating string (at the first fret). Since the height of the fret wire varies from one manufacturer to the next, and the amplitude of the vibrating string depends upon the player's attack and the type and tension of strings used, there is no universally correct dimension for string height at the nut. Instead, it is necessary to set the string height at the nut based upon both theory and the particular preferences of the player. The method described below for adjusting string height at the nut is very similar to that given by Dan Erlewine in his book "Guitar Player Repair Guide". The tools necessary for this adjustment are a short straight edge (ruler), a standard set of feeler gauges and either a set of calibrated nut files or an X-acto saw and a tear- drop needle file. Feeler gauges are thin, accurately calibrated metal strips that are used for gauging the size of a gap. The feeler gauges need not be a special set; they can be obtained from any auto-supply store, or hardware store or purchased from a luthier supply house. Nut files are special files that are manufactured to cut a round-bottomed slot of a particular width. Although a complete set of nut files includes widths ranging from .010" to .058", a "starter" set consisting of .016", .025" and .035" widths is quite adequate. While nut files are easy to work with and remove much of the guess work from nut slot filing, they are expensive, and not essential. An excellent alternative is to purchase an X-Acto saw blade which attaches to a standard X-Acto knife handle and one or more needle files. The saw and handle is available at hobby shops, is inexpensive and is very useful in cutting nut and saddle materials. Small tear-drop shaped needle files are available at hardware stores and hobby shops in at least two different sizes and can be used very effectively for cutting the slots in guitar nuts. Begin by measuring the height of the first fret. One way of measuring this is to place a straight edge on the top of the first two frets, so that it straddles the first and second frets, and then slide feeler gauges - individually, or stacked - between the fingerboard and the straight edge, until the gages just fill the space between the fingerboard and the straight edge. (The straight edge runs parallel to the strings, while the feeler gages are inserted from the edge of the fingerboard parallel to the frets, midway between frets one and two.) A typical fret height is about .040". To the fret height you measure, add about .008", which is about the amount by which the string will vertically clear the first fret. This total is the approximate height above the fingerboard that each string should be. Stack the appropriate combination of feeler gauges to obtain a combined thickness of the calculated value. Reduce the tension on the first string sufficiently that you can lift the string out of its slot and slide it towards the second string, letting the first string rest on the top of the nut. With all but the first string at full tension, place the end of the stacked gauges on top of the fingerboard so that the edge of the gages are touching the nut. The gages are inserted under the first string from the treble side of the fingerboard so that the length of the gauges runs parallel to the frets and all but the first half of an inch or so overhangs the edge of the fingerboard. | | stacked gauges | | | | edge of fingerboard ......... |............................. . . | | 1st string slot.-------. | | ----------------------------------------first string . . | | . . | | . .---------- | . . | . . first fret nut Enlarged Top View of Nut Area Using either a nut file or the X-acto saw, deepen the slot until you just begin to contact the top surface of the stack of feeler gauges with the file or saw. The slot should be filed (or cut) so that the string breaks over the nut at the leading edge of the slot - at the face of the nut nearest the bridge. This is accomplished by filing or sawing the slot at a downward angle from the fingerboard towards the head. Failure to have the string break at the leading edge of the nut can result in poor intonation and string buzz. The width of the slot should be several thousandths of a inch larger than the diameter of the string. If the slot is too narrow, the string will bind in the slot, causing premature string breakage. One symptom of a binding nut slot, in addition to frequent string breakage, is that the change in tension in the vibrating portion of the string does not occur smoothly when adjusting the tuning pegs; the string's pitch changes suddenly, lagging behind the adjustment in the tuning peg. Once you have filed to the appropriate depth, remove the stack of gages, reposition the first string and return the string to full tension. Repeat the process for the second string, sliding the stack of gages beneath the first string and extending under the third string. When completed, repeat the process for the third string. To adjust the height of the fourth string, insert the gages from the bass side of the fingerboard and repeat the same process. Repeat for the fifth and sixth strings. As a subtle adjustment, I often vary the nut height by about two or three thousandths of an inch from first to sixth strings, with the first string being lower than the sixth. RAISING THE STRING HEIGHT AT THE NUT If you found that the string height at the nut was too low, or you cut the string slots too deep, the string height at the nut can be increased. One common way of increasing the string height at the nut is to place a shim beneath the nut. To do this, remove the nut, cut a shim to the same width as the nut, glue the shim to the bottom of the nut and reglue the nut to the neck. Guitar necks are commonly made from mahogany or maple, and shims can easily be made from a matching veneer, and if necessary, the visible edge of the veneer can be stained with an appropriate color of felt tip pen. Once the nut has been shimmed sufficiently, the string height can then be lowered, if necessary, using the same procedure as described above. NEXT.... Setting Intonation, Basic Guitar Set-up Part 4