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William Cumpiano's
String Instrument
Newsletter #7

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The Neck-Angle "Value"

William R. Cumpiano 1998, All Rights Reserved

In earlier columns I talked about the neck angle, and the set up. The set up was a series of adjustments to optimize the guitar's playability. In all cases, the final arbiter of how well a guitar could be set up was if it's neck angle was correct--and if it wasn't, what the set up could accomplish to optimize the instrument's playability within the givens of the less-than-ideal neck angle. With this subsequent series of articles, I'll delve into the topic of neck angles and when the set up fails to make the instrument marginally playable, what to do next.

If a friend asked you to evaluate a guitar, you might first check its condition, or its brand, and probably would strum it to judge its sound. And indeed, all these would tell you something about its quality.

But there is another subtle, often-overlooked factor that enormously affects the inherent quality of any fretted string instrument. It directly determines how easily the instrument can be made to play; and indirectly governs how accurately its intonation can be set. It also determines how much stress is being "dumped" onto the guitar by its strings -- in turn contributing to the loudness of the tone and the longevity of the structure.

This marvelous quality can be exploited in full measure by a thoughtful builder -- or neglected by a ignorant builder or one intent on cutting corners. The ignorant and the hasty miss it because it requires great skill to impart, even to identify. And because a guitar is a delicate, highly stressed structure, the conditions relating to this quality factor can be difficult for a maker to assure or a repairman to impart when it's not there. Alas, this quality factor is perishable, something lost over time. We lack a single word to describe the factor, or the conditions relative to it; but we do have a term for the physical relationship of the components which are at its heart: the neck angle (also referred to as the neck's pitch, tilt, or inclination). This is the angle formed by the fretboard relative to the face of the guitar.

Crucial Relationships

Simply, it determines the height at which, with a given bridge, the string array will be suspended over the fretboard of the guitar. Clearly then, string height over the fretboard, string height over the soundboard, bridge/saddle height, and neck angle all are vitally interrelated.

As is well know by most players, tiny variations in the strings' height dramatically affect a guitar's playability. Less well known is that the string height also largely determines the "leverage" the string exert on the instrument as a whole. This in turn affects the loudness of the tone and the life span of its structure. The builder or technician must impart to the neck an angle (relative to the face of the guitar) that is correct for that particular instrument, according to its structure and intended use.

I often am consulted by people asking me what to "look for" when buying an instrument, be it new or used. I usually caution that buying a guitar is very much like buying a painting -- a great deal of one's appreciation for a guitar is on a very subjective, personal level. But to the extent that a buyer can ascertain if a guitar will "work" properly -- that is, be an efficient and long lasting tool for musical expression -- the best advice I can offer is this:

"After verifying that the fretboard is reasonably straight, look for LOW action and a TALL saddle. No, not a high action and a high saddle, or low action and a low saddle -- but especially not a high action and a low saddle.

A Touchstone

The existence of the combination of a low action with a tall saddle reveals a wealth of information about the instrument. More than anything else that can be recognized at a glance, it indicates the thoughtfulness of the builder and the success of the design. It foretells a long working life of easy playing, with few adjustment costs. It reflects the correctness of the neck angle. It is a reliable sign of good value -- and is, incidentally, a very rare condition!

Before I overstate my case, I must point out that too much of a good thing is as bad here as anywhere else. Generally the ideal situation is that 1/8-inch to 3/16-inch of saddle should poke out over the bridge surface; and not over 1/8-inch of airspace between the fret and string, as measured at the 12th fret. This is neck-angle "value" at its highest. The closer a guitar is to this ideal, the better.

Bottom Line

The neck angle determines the inclination of the fretboard -- which is what matters. If the inclination is correct, it guarantees the strings a useful range of action-height adjustments, while maintaining a string over the face, at the bridge, that is appropriate to the guitar's design and structure.

A trick question that is often asked in this context is: "Do you check the angle to see whether the neck is warped?"

Because warp means different things to different people, it is important that a builder/technician keep the distinctions perfectly clear. To a carpenter, "warp" is a precise technical term. It is distinct from "twist" or "cup," and often refers to how a plank of wood can become distorted, usually as a response to moisture changes in its environment, or to inherent problems dating from when the plank was cut, or from the way it was dried.

However when a plank or guitar neck takes on permanent distortion from continuous stress (as might the shelf under you set of encyclopedias, or a 12-string tuned high with heavy-gauge strings), it is best to say the wood acquires a "set."

The guitar's neck of course, is threatened by warpage, setting and more. Most luthiers and instrument technicians have seen necks that have twisted, as well as necks with a lump or "king" at a spot suspiciously near a swirl in the grain. And they've seen necks tortured by being placed in four-wheel solar ovens -- automobiles -- that have curled, and stayed that way after cooling, even after the strings were taken off. But let's allow the uninitiated observed to refer to all these as "warped" necks. A warped neck can usually be remedied by a variety of clever repair techniques. Some are simple and some are not, but all result in the coaxing of the "wrinkled" fretboard back to a state of relative straightness.

More Problems, More Risks

Let's keep all these distortions distinct, however, from problems in the neck's angle, which involve precisely how the entire neck has been attached to the body at the neck joint. The angle changes only if the entire soundbox/heel structure distorts -- or if that crucial joint loosens and fails.

With few exceptions, the only good reasons for purposely changing the neck angle are if it was never right in the first place (and that, sadly enough, is too often the case); or if string tension and time have caused the entire structure to "set" permanently into a lengthwise bow away from the strings.

Simply, making a change in the neck angle is a serious last resort. It is performed when no other localized repair or action adjustment can improve the action height, or change the height of the guitar's saddle without seriously compromising the instrument in other ways. Unless done with the utmost skill, the procedure can result in permanent scarring of the instrument to some degree. One error can mangle the guitar and ruin its value.

How To Proceed?

Often, changing the fretboard's inclination is accomplished by altering the neck's angle at the neck/body joint. This is done by removing the neck, recutting and rebuilding the mating surfaces of the neck joint, and reattaching the neck. But in many cases, the structure of the guitar forbids changing the neck angle at the joint by any means: with traditionally built classical guitars, and on neck-through-body electric guitars, the fretboard inclination is changed by planing a new incline angle into the existing fretboard surface (refretting, of course becomes necessary), or creating a new incline by placing an inclined shim under the fretboard.

The decision to act and the choice of the method require a fair amount of experience, prudence, and the knowledge of guitar structures: Imagine the mayhem resulting from trying to bully off a neck on a guitar that has no neck joint! Or from trying to steam off a neck held in place by pins, or bolts! And after the neck is off, it must be reattached anew, and permanently: its new inclination differing by scarcely two or three degrees from it's original state! Good nerves and a steady hand are de rigeur.

Action and Options

The importance of having a range of action heights available on a guitar is self-evident. It clearly is a valuable option to be able to adjust the strings close to the fretboard for light, quick playing -- and also to lower the strings when a guitar's soundboard arch swells during a humid season, thus jacking up the entire string array. Besides an excessively high action will cause notes to fret progressive sharper in pitch up the fretboard to an unwanted degree: lowering the action often brings the guitar's intonation back into line.

Conversely, if the player wants to "work" the string more vigorously -- or when a dry spell flattens the face on the guitar -- an increase in saddle height is in order. If the neck angle is correct, that adjustment can be done without the result being a grotesquely, dangerously tall saddle.

A proper neck angle allows all this variability. An improper angle usually leaves the guitarist stuck with low action, because the saddle already is excessively high; or with high action, because the saddle is excessively low, or even gone altogether. The importance of the proper string height over the face of the guitar is less obvious -- but just as crucial. The higher the strings are above the soundboard, the greater their effect on the soundboard -- a simple matter of leverage. Imagine the torquing effect of the bridge on the soundboard as being like that of a crowbar on a nail. Raising the string (by making the bridge thick, installing a taller saddle, or both) is like lengthening the long arm of the crowbar: it increases the mechanical advantage, The same tension dumps more stress on the top.

The Cart, The Horse

Thickening or thinning the bridge, however, changes the acoustical anatomy of the soundboard dramatically. Raising and lowering the saddle also changes the "back-angle" of the string (the angle formed by the string as it drops over the saddle into the bridge. Readers of this newsletter should be well acquainted with this issue, since it was treated exhaustively in an earlier issue) and can also alter the perceived stiffness of the strings and the attack, sustain, and decay envelope of any plucked note. Thus, there is a hidden price to pay in sound and "feel" when you choose to change the bridge or saddle to remedy action problems cause by a bad neck angle. It is far better to first decide what the most prudent bridge thickness, saddle height, and string back-angle should bee -- and then work to insure that the neck angle be correct to afford the optimal action-height range: Voila! The best of all possible worlds!

Regrettably, only a handful of careful builders do it this way. The industry standard, at least when I last looked, is to grind down an oversized bridge to suits whatever neck angle comes down the line on each guitar. Thus we see Gibson, Martin, and Guild acoustic guitars with a variety of different bridge thicknesses and saddle height -- and, not so mysteriously, quite a range of different sounding and feeling instruments within an otherwise identical batch of guitars. To cover my tail, this was apparent to me when I was an active repair jockey, years ago. My leaving the repair field in favor of building full time has put me out of touch with what the big guys are doing nowadays. I hope, and expect, that with the proliferation of CNC technology, they are building more consistently today.