Oskar Graf – August, 2001
I would like to thank Tom Blackshear for inviting me to participate in the Luthier’s Showcase. I’m a bit of a hermit living here in the wilds of Eastern Ontario and I tend to forget that there is this great network of guitar builders and players out there. It’s been very stimulating to read, and some of the ideas will surely percolate all summer long and then pop up when I build my next season’s guitars
I’m a bit concerned though, that I might not meet the expectations about revealing all my secrets of fine tuning my guitars. That’s not because I’m such a secretive fellow but more because I’m a very unscientific builder, more one of the artsy variety, and so I find it hard to make very definitive statements about the subject.
As builders we each bring different skills and backgrounds, personal and cultural, to guitar making which have a major influence on the outcome of our work. I have come to call this “the maker’s interpretation of the idea of guitar”. Even if we try to copy a well-known maker’s guitar, there will be personal touches and interpretations that give each one our personal stamp. Once we open this up to our own classical guitar designs, the variety and permutations become infinite and show a lot about the personality of the builder.
In this forum we have gone quite a few times through the cycle of guitar building with great technical detail. I will get to a few technique points too, but I thought that I will keep my musings more to the underlying thoughts and decisions that I make when building a guitar. I see “fine tuning” as a process that is part of every step in building, so that ideally, I don’t have to fine tune my guitars once they are completed. That’s not to say that at times I‘ll remove the strings, get in there, and sand some braces to try getting the sound I want.
I’m basically self-taught and, like everybody else starting out, read as many books on building and acoustic theory of stringed instruments as I could find. This answered the basic “how to” questions, but exactly how thin I should plane that top, or how do I get sound I want, still stayed a mystery. Quite early on I took a guitar building course by David Rubio at one of the Toronto Guitar festivals. When asked how he gets his sound, he said something like this - “You have to keep your sound ideal in your mind (ear) and work towards it.” Now that sounded pretty nebulous to beginning luthiers looking for a definitive answer, but I have come to realize that there was a lot of truth in it.
The sound I have in my head, mind, changes over time, it’s influenced by the musical culture of our time. New guitarists and changes in concert repertoire make me listen to the guitar differently and in the end change my sound ideal
I have always relied more on my senses, rather than measurable data, to make decisions in building. I believe that if we trust ourselves, we are capable of making very fine distinctions in sound, texture and shape.
In the beginning that was pretty nerve wrecking because I had no experience to guide me, so to sharpen my senses of touch and hearing I made a point of not keeping any journals of building but relied only on my memory. In a way it was to internalize the information, to make it part of my body memory.
Top Thinning and Graduation:
A lot has been written about wood selection and I don’t want to go through it again. I do the tapping, listening and flexing, and sensing of the density and weight. I find that just stroking the rough-sawn top lightly, I get a lot of tonal information. Each species of wood has its own mix of information and I don’t use the same selection criteria for cedar that I use for spruce. After this rough selection, I plane the tops that I’m using that season to a bit over 3 mm, then join them and store them till final selection.
Nearly all of my instruments are built to order. The more input the player can give me by playing for me, as well as telling me about preferences, the more of a vision of it I have to guide me in the building process. Selecting the top might mean choosing a lighter rather than a heavy dense spruce, bear-claws or straight grain. All will make great guitars but with slightly different characteristics. As a general rule I feel that heavier wood produces a bit more fundamental sound spectrum.
All further thinning and graduation of the top is done by hand. I use an old Ulmia Reform plane that I brought with me when I immigrated. I like the process of hand planing because it gives me time to listen to the tonal changes as I thin the top. There’s also something about the quietness of it that makes concentrating and the retaining of sensory information easier. I’m not listening for a specific pitch or frequency but the quality of the sound: clarity, bell like or woody, the sustain, the shifts in frequency as I thin the top. At the same time as I’m handling the top, I get a sense if its stiffness and resilience. Cedar can be very stiff but is quite brittle; you always worry that it’ll crack if you bend it just a bit too much. Spruce can be just as stiff but is more springy, resilient.
So when to stop - it’s the age old question. I know that point quite well, but it’s so hard to describe, something like when the clarity drops off just a bit, sound becomes more woody, sort of just over the edge. I approach this point in several steps. At first I work with the cut-to-size, somewhat rectangular top. When I get close, I cut the top to the guitar shape, and start graduating. I thin the lower bout edges by 0.1 to 0.2 of a mm; the back edges, most of the time, are thinned a bit more. I might take a bit more off in the center too, until the stiffness and sound feel just right.
My spruce tops are somewhere between 2.2 mm to 2.5 mm at the center, the odd, really hard and heavy grained top, even thinner. Cedar being that much lighter, I keep around 2.5 to 2.65 mm. One other consideration in the final thickness and graduation of the top is the bracing pattern that I’m going to use. To me the whole thing is in finding the balance between the top and the bracing.
In my work as a designer I learned to combine technical, structural aspects with the artistic, and honed my skills for proportional relationships. I found that to be a very useful skill to have in my guitar work. In analyzing existing fan bracing patterns, or when I develop my own ones, I look at the relationships between the braces and the spaces in between and see the whole pattern as a visual design.
In the fine tuning, or the balancing of the top and the braces, I work with the spread of the fan, the length of the bridge plate, and the length of the diagonal struts at the bottom. On the spruce top plan, the fan braces don’t meet the harmonic bar, so I can adjust the distance from the end of the braces to the bar. All these are not dramatic shifts, generally just a few millimetres, and they depend on my sense of the quality of the top.
I glue the braces on as square strips of equal height and then shape them to size with a small plane and a chisel. I have a general guideline for the heights of the braces, but the final height and shape is arrived at very carefully. I tend to alter the cross section shape as I go from treble to bass, form a pointier, triangular shape to a more rounded parabolic shape. The slope towards the harmonic bar ends in a straight line to the top; the back ends are scooped and feathered out as they meet the diagonal struts. I like to arrive at a sculptural look; the transitions are smooth and gradual as if the braces grow out of the top and then blend back in.
Throughout this process I flex, tap and listen to the changes in tone, keeping in mind that notion of tone that I like to achieve in my finished guitar. This point is even harder to describe than that of thinning the top, or achieving a certain clarity in the intervals from treble to bass, or getting the right amount of flexibility across the top as well as length wise. Just a sense that ‘this is it’.
Body fine tuning:
Once the top is glued on, and I glue the top on after I glue the back, I can get a sense of the way the top and the body resonances work together. It’s tempting to make adjustments right away but I wait till I have the binding process completed. I find that there is a marked tightening up of the box that changes the sustain and makes odd frequencies easier to hear and feel. The tuning involves tapping, flexing the edges of the lower bout, getting a sense of it’s stiffness, singing or humming into the sound hole and sensing the vibrations in the top. I might plane the top edges a bit more, or even sand the whole top, but I rarely go inside to work on the braces.
I glue my bridges on after the top has been polished and the bridge has also been finished so I don’t have a way of tuning with the bridge. However after reading some of the contributions on this subject, I might rethink my process in this area. My bridges are quite light and of traditional design, with the exception of the arms which I taper in height as well as width.
After stringing up I like to let the guitar settle in for at least 14 days before I make any judgments about further fine tuning. As I said above, it’s not often that I do this, so it’s certainly not a refined system. I do that to clear up some dull notes or what I perceive as mismatches between the top and body frequencies. I work only on the fan braces, mostly on the first and second outer ones. To lighten the braces I sand the sides of braces, making them slimmer. To get a bit more flexibility around the edges, I work on the end slope of the braces; this tends to help the high end. Using sandpaper is a pretty slow process but it actually takes very little to affect a change.
....and to turn just about anything I have said here on it’s ear, I have been working on cedar top lattice-braced guitars (not a Smallman copy) over the last few years and right from the start they have turned out very well. However, all my ways of guiding me though the process, the tapping and flexing and so on, are pretty much useless, because the design parameters are so different. It’s a whole new learning curve that I have to go through to get a handle on this new design. Well that’s what keeps it all so interesting, the never ending search for the perfect guitar.
By the way, I’m still working with the traditional fan bracing; there’s still a lot of sound potential that hasn’t been explored. I could rattle on and on but I hope that I have revealed my approaches to fine tuning, and any secrets that remain are unintentional.
Happy guitar making, may the sound be with you!