From the November/December 2019 issue of Acoustic Guitar | BY MARTIN KEITH
I play a Martin D-28SW. I have been using medium-gauge Martin Monel Tony Rice strings for several years and like them a lot. Some of the strings, particularly the wound third, get a little stuck when I am tuning. If the string is a little sharp and I tune it down, the pitch drops too far. When I tune back up, the string goes too sharp, with a little clicking sound. How can this slight but annoying tuning problem be fixed? —Bill Pramuk, Napa, CA
What you’re experiencing is a very common problem—and, happily, one that’s easily remedied.
It relates to the size and shape of the slots in the nut, which is a critical area where a few thousandths of an inch can make a big difference in your comfort, intonation, and tuning stability.
The click you hear is the sound of string tension being released from one side of the nut to the other. This is quite possibly due to the larger gauge of the Monel strings you mentioned, which at .013–.056 are heavier than the .012–.052 set Martin likely installed on the guitar during assembly. Thicker strings will require the nut slots to be widened, ensuring that they can pass freely through the slots without any binding or pinching. Because of the break angle (the angle change between the fretboard and the headpiece) there will always be some downward pressure from the string, so it’s important that the slot be shaped and finished correctly, as well as sized appropriately.
When correctly cut, a nut slot should have a U-shaped profile—straight walls and a half-rounded bottom. A common problem is slots with a V shape—in these cases, downward pressure causes the string to wedge itself into the narrowing bottom of the V, and inevitably the string will pinch and bind as a result. The slot bottom should be smooth and free of “chatter marks,” the rough texture caused by incorrect or incomplete filing. I usually size nut slots anywhere from .003–.006 inches larger than the stated string diameter. This avoids any potential friction, even in cases where the player goes up a gauge.
Nut-slot depth is the other parameter that has a big impact. If the slots are filed too deeply, the open strings will buzz and the nut will require replacement or repair. However, the much more common scenario is that the slots are shallow—in this case, the strings will be too far above the frets. As a result, simply pressing the strings to the frets will bend them sharp. This effect will be most noticeable in the first few positions—and since that is where one usually includes open strings alongside fretted ones, it is usually very noticeable. During setup, most luthiers use feeler gauges or other measuring tools to dial in a nut depth that allows minimal clearance above the frets without buzzing. Different players and playing styles sometimes require specific tweaks—if you’re an open-position strummer, your ideal setup may well be different from that of a fleet-fingered soloist.
This would be a good moment to mention the wide range of nut materials that are available. Traditionally, nuts and saddles were made of organic bone, which is plentiful, durable, easily worked with hand tools, and can be polished to an attractive finished surface. Some vintage instruments even have ivory nuts—thankfully, that is no longer done! Bone remains the standard against which other materials are evaluated, and there is a widespread belief that it is still the best choice for tone.
However, many other more modern materials have proven themselves as viable alternatives. In the 1970s, brass nuts were very popular, and a well-cut brass nut can perform quite well. (Frets themselves are made of a brass alloy, after all.) Synthetics such as Corian, Delrin, carbon fiber/graphite, and other composites are increasingly used in both production guitars and handmade instruments, and they offer some compelling advantages compared to the old standard: they are easier to machine without chipping or cracking and can in some cases be molded to very close tolerances, allowing for quicker and more accurate setups in a factory setting. Some nut materials also incorporate graphite and other self-lubricating materials, which help alleviate pinching and binding issues.
Finally, composite materials are much more uniform and homogenous—bone, as a natural material, varies quite widely in strength, density, and resilience, and not all pieces are guaranteed to make good nuts. For these reasons, many manufacturers have gone over to composites for these parts, with excellent results—factory setups on acoustic guitars have steadily improved in the last 15–20 years, which is great news for players at every level.
There is considerable debate among players about the effects of nut material on tone. The loudest voices in these discussions are usually those advocating for bone, and it’s quite true that the classic American flattop tone includes bone nuts and saddles, however large their contribution may be. But there are countless factors that affect the tone of any given instrument, and many of them are much more significant: the properties of the top, back and side material, size and position of the bracing, stiffness of the neck, and many more. Next to these fundamental properties, nut and saddle material make, in my experience, a relatively small impact—and in the case of the nut, an impact that is only heard when playing open strings. A great guitar will be great regardless of the nut material, and a poor one usually can’t be saved by a magic piece of bone.
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Ultimately, the nut setup is far more important than the material—a poorly adjusted nut will make a guitar difficult to play, hard to keep in tune, and impossible to intonate—and that will be far more noticeable than any little tone difference I can imagine!
A qualified luthier should be able to fine-tune the nut for your strings in relatively little time, and you will likely notice benefits to your action and intonation, as well as your tuning stability. These adjustments have possibly the most bang-for-your-buck of any investment you can make in your setup, and they will pay off every time you pick up the guitar.
Martin Keith is a luthier, repair and restoration expert, and working musician based in Woodstock, New York. martinkeithguitars.com
This article originally appeared in the November/December 2019 issue of Acoustic Guitar magazine.