Walnut & Sitka OM
Posted: Sat Jan 17, 2015 3:21 pm
This is my first build, which I finished a few months ago but just got around to photographing and writing up. It's a fairly straightforward OM-size design but with a few uncommon features. I started out following Kinkade's book and got as far as bracing the plates when I obtained Conptemporary Acoustic Guitar Design & Build by Trevor Gore & Gerard Gilet (which I'll refer to as G&G for brevity) and the rest of the construction is mostly based on their design, including a bolt-on bolt-off neck.
This is scratch built, with most of the wood coming from LMI. The back and sides are black walnut, with sitka for the top and all the bracing. Bindings are curly maple. The neck is Spanish cedar and the fingerboard is Honduran rosewood, which I chose because it's a good color match for the walnut. It's all finished with U-Beaut hard shellac following the "advanced French polish" techniques in G&G, using an azeotropic solution made by adding acetone to the base shellac mix so it dries about as fast as it's applied. It's semi-pore-filled so there are quite a lot of open pores but not as much as raw walnut. The rosette is a simple herringbone inlay that I bought from LMI, and I made the end flash as a stylized "tree" so unlike most tapered end flashes I've seen, the pointy end is toward the soundboard:
I liked the idea of a straight string pull headstock as described in the G&G books but I really prefer the look of a symmetrical shape, so I designed the headstock to give a very nearly straight string pull but using a symmetrical layout. The "mini" Gotoh tuners have the screw tabs pointing downward so that I could get them very close together in the center. When I worked out the geometry I neglected to account for the thickness of the low E string so it bends in just a little, nothing that would hurt the tuning but in the future I'll space the tuners just a bit farther apart. I left enough room for an inlay on the top of the headstock and I may go back and retrofit an inlay into this one at some point (glad I made the bolt-off neck). I made the compensated nut following the G&G specifications and the intonation came out really good, within a couple cents of chromatic on every string and every fret.
I came up with the ellipse-in-ellipse bridge shape to echo the arched headstock. I used black walnut as it's one of the woods G&G recommend, much less dense than ebony for example but having sufficient stiffness and resistance to crushing. I decided to angle the grain in order to make it a bit more resistant to splitting across the peg holes, and the bridge plate underneath has its grain running diagonally in the opposite direction, about 30 degrees from horizontal. The bridge is just wide enough that the shoulders of the ellipse lie fully over the X braces underneath. G&G recommend no less than 49 square centimeters of gluing area, and I know it's just a guideline but I made mine exactly 49 centimeters in area. I thinned down the area behind the strings to save weight and also to make it thin enough to flex just a little as the soundboard distorts under string tension, which I think should make it somewhat less susceptible to glue failure in that area. I also angled the saddle slot by 2 degrees relative to the strings, contrary to G&G who use a perpendicular slot, so I was able to save weight by using a thinner saddle and still had enough width to make the required compensation ramps. In the end the bridge weighs 18 grams, plus about 5 for the saddle. That seems pretty decent but in my next builds (which I'll post soon) I was able to keep this basic design but shave another 5 grams off the total without sacrificing any gluing area.
Here's a short sound clip, just me playing a little open chord melody, and I'm not yet proficient enough to exercise the full range of the fretboard so honestly I don't know how it compares to other guitars but I think it sounds decent. To my ears it seems to have a nice rich bass, which I expect is largely due to the deep body. I haven't done a frequency analysis as described in G&G yet but as far as I can tell it doesn't have any wolf tones or other sonic problems and I haven't had any problems with fret buzzing. I took it to Elderly Instruments in Lansing where Joe Konkoly was kind enough to give me a critique of this guitar and my next one. His main recommendations were to lower the action (I made it 2-3 mm following G&G but Joe makes his about 0.5 mm lower) and to make the neck profile more tapered on the sides, which seems like good advice as the neck does feel quite chunky to me. Fortunately with the bolt-off neck it would be easy to remove and reshape it so I may do that at some point.
This is scratch built, with most of the wood coming from LMI. The back and sides are black walnut, with sitka for the top and all the bracing. Bindings are curly maple. The neck is Spanish cedar and the fingerboard is Honduran rosewood, which I chose because it's a good color match for the walnut. It's all finished with U-Beaut hard shellac following the "advanced French polish" techniques in G&G, using an azeotropic solution made by adding acetone to the base shellac mix so it dries about as fast as it's applied. It's semi-pore-filled so there are quite a lot of open pores but not as much as raw walnut. The rosette is a simple herringbone inlay that I bought from LMI, and I made the end flash as a stylized "tree" so unlike most tapered end flashes I've seen, the pointy end is toward the soundboard:
I liked the idea of a straight string pull headstock as described in the G&G books but I really prefer the look of a symmetrical shape, so I designed the headstock to give a very nearly straight string pull but using a symmetrical layout. The "mini" Gotoh tuners have the screw tabs pointing downward so that I could get them very close together in the center. When I worked out the geometry I neglected to account for the thickness of the low E string so it bends in just a little, nothing that would hurt the tuning but in the future I'll space the tuners just a bit farther apart. I left enough room for an inlay on the top of the headstock and I may go back and retrofit an inlay into this one at some point (glad I made the bolt-off neck). I made the compensated nut following the G&G specifications and the intonation came out really good, within a couple cents of chromatic on every string and every fret.
I came up with the ellipse-in-ellipse bridge shape to echo the arched headstock. I used black walnut as it's one of the woods G&G recommend, much less dense than ebony for example but having sufficient stiffness and resistance to crushing. I decided to angle the grain in order to make it a bit more resistant to splitting across the peg holes, and the bridge plate underneath has its grain running diagonally in the opposite direction, about 30 degrees from horizontal. The bridge is just wide enough that the shoulders of the ellipse lie fully over the X braces underneath. G&G recommend no less than 49 square centimeters of gluing area, and I know it's just a guideline but I made mine exactly 49 centimeters in area. I thinned down the area behind the strings to save weight and also to make it thin enough to flex just a little as the soundboard distorts under string tension, which I think should make it somewhat less susceptible to glue failure in that area. I also angled the saddle slot by 2 degrees relative to the strings, contrary to G&G who use a perpendicular slot, so I was able to save weight by using a thinner saddle and still had enough width to make the required compensation ramps. In the end the bridge weighs 18 grams, plus about 5 for the saddle. That seems pretty decent but in my next builds (which I'll post soon) I was able to keep this basic design but shave another 5 grams off the total without sacrificing any gluing area.
Here's a short sound clip, just me playing a little open chord melody, and I'm not yet proficient enough to exercise the full range of the fretboard so honestly I don't know how it compares to other guitars but I think it sounds decent. To my ears it seems to have a nice rich bass, which I expect is largely due to the deep body. I haven't done a frequency analysis as described in G&G yet but as far as I can tell it doesn't have any wolf tones or other sonic problems and I haven't had any problems with fret buzzing. I took it to Elderly Instruments in Lansing where Joe Konkoly was kind enough to give me a critique of this guitar and my next one. His main recommendations were to lower the action (I made it 2-3 mm following G&G but Joe makes his about 0.5 mm lower) and to make the neck profile more tapered on the sides, which seems like good advice as the neck does feel quite chunky to me. Fortunately with the bolt-off neck it would be easy to remove and reshape it so I may do that at some point.