I've always been a fan of the sound of both the mandolin and the 12-string guitar, so I got this crazy idea of trying to build a hybrid of the two.
The first thing was to decide what scale length to use, a guitar is about 650mm when a mandolin is about 400mm, so a nice and round number would be 500mm. That's about 25% shorter than a standard guitar, so of course the size of the body should be reduced about the same amount. The "Dreadnaught" body shape has always been my favourite so that was a easy choise. The next thing was to decide how many strings and the tuning was to be, which eventually turn out to be the standard 12-string tuning, just because of the simple fact that if I would have made it some sort of mandolin tuning I wouldn't be able to play it myself, because I only know some basic guitar chords.
Perhaps the most crucial part of an acoustic guitar is the bracing of the top. The bracing serves two functions, it strengthens the guitar, and the size, shape, and angles of the bracing can be used to "color" the tone. Top quality acoustic guitars primarily use high density spruce, with the grain aligned vertically. The grain is vertical because the wood is quartersawn, which makes it much more difficult to break than weak wood with no particular grain alignment. The high strength to weight ratio means that the braces can be scalloped to reduce weight but maintain the strength. The lighter weight braces allow the soundboard to vibrate more freely, which gives the guitar a fuller, warmer, and richer tone.
I had no idea what to make of it, after all the bracing is a fairly complicated and detailed construction. I looked around on the internet and found two interesting books about acoustic guitar building on a online bookstore.
The first one was the "Guitarmaking: Tradition and Technology" by Jonathan Natelson and William Cumpiano, and the second was "Build Your Own Acoustic Guitar" by Jonathan Kinkead.
I couldn't decide which type of bracing to use so I simply decided to build two guitars at once, one with the classical style bracing and the other with the x-bracing design.
Since the scale length on this build is about 25% reduced (compared to a normal guitar) the string tension is also reduced. However, this would be a 12-string (not a normal 6-string) so the overall physical strain that the top and bracings would have to withstand would approximately be the same as on a full-sized top. So what I did was basically use the same dimensions on all the bracings only reducing the length to proper measurements.Once I found the standard string spacing measurements on a 12-stringed guitar the fretboard shape had to be calculated, and the fret distances calculated according to the scale length. All the templates had to be drawn for the head and the body shape, and a jig was made out of MDF for the bending of the sides. Basically three pieces of 16mm thick MDF cut out to the proper body shape and some spacers in between the pieces to achieve the 80mm thick jig that was needed.
# of strings:
Type of bracing:
Top wood, thickness:
Back & sides wood, thickness:
Fretboard wood and thickness:
Number of frets:
Darco Phosphor Bronze
Dunlop medium 6S
Osmo Color Wood Wax
Dunlop medium 6S
Graph Tech Tusq
Pearl and abalone
So the planning and preparations was done, more or less, so it was time to get working...
All the pieces was cut, planned, glued and sanded to the dimensions required. The most intricate work on a acoustic guitars top is probably the rosette (the ring that surrounds the soundhole), it basically serves only two purposes; it strengthens the soundholes edges, and is decorative. A soundhole without a rosette would probably look all wierd, ugly and cheap. I had this idea of using a small piece of zebrawood I had salvaged from somewhere, cut it into 3mm thick pieces. Penciled out the inner and outer diameters of the ring I knew I had to make out of this, wedge-shaped all the small pieces to get them to line up in a uniform circle, and glued them all onto a thin piece of MDF. Once the glue had dried the ring was cut out with a circle cutter on the drill-press and the ring separated from the MDF with the bandsaw.
Next was the grooves that had to be cut into the top, and the soundhole along with them. Measured and marked the positions and adjusted the circle cutter accordingly. Caution is required since the top is only 3mm thick and the grooves can't be any deeper than 1-1½mm.
Once the grooves were cut out, the gluing of the zebrawood ring, abalone and black-white-black linings was done with superglue (CA glue). When the glue had cured the ring and linings was scraped and sanded flush to the tops surface.
So next was the other side of the top, the bracings, which is the main structural element for the guitar top. It does the job of supporting the tension placed on the top by the strings. Its’ second job is to distribute vibrations from the strings over the entire surface of the top.
While the classical guitar has a lot more variety in bracing patterns than does the acoustic guitar, there are a few notable bracing patterns that have become a standard in the acoustic guitar making industry.
In the 1930’s C.F. Martin rose to the top as the leader in steel string acoustic guitars. They led with such innovations as the Dreadnought body shape, the 14-fret neck (the neck actually joins the body at the 14th fret), top X-bracing patterns that are still the standard in today’s market.
The braces (or sometimes also called struts) are made from split, straight-grained quarter-sawn spruce. To achieve maximum stiffness the end grain should be vertical. I rough-cut all of the bracing to length and width, and those bracings that had to be a bit curved was planned and sanded to the correct shape according to the plans.
The position of all the braces was marked on the tops using the cardboard templates, both the classical bracing and the x-bracing. All the braces can't be glued in place at once, so only 1 or 2 braces was glued and let to dry for about 30minutes.
A perhaps less common wood glue was used throughout the build, a aliphatic resin (sometimes called AR glue). Aliphatic resin glue is what we commonly know as “yellow glue” or “carpenter’s glue”. It is similar to PVA (white glue), but has been modified to make it stronger and more moisture resistant and has special properties especially designed to be used on wood-to-wood bonds. Titebond Original is one of the most common aliphatic glues sold in the US. Very inexpensive and and great choice for a go-to interior wood glue. It dries in 10-15 minutes and fully cures in 24 hours. It "grabs" fast, is sets hard, it's resistent to thermoplastic "creep" and the bond formed is very strong and sandable without balling up or softening. It is also water-soluble for easy clean up.
Once all the bracings was glued and properly dried it was time to shape and scallop them according to the methods in the books, and finish everything off with some sanding.
The bending of the sides was something new to me, usually it's done by steaming the pieces inside some sort of oven for some time to get the wood as moist and hot as possible so it can be bent into shape without cracking. The making of such a oven didn't seem very "cost- and time-effective" to me, so I got this idea of using a short piece of rainwater metal gutter. Attached gutter ends with heat-resistant glue and voila'... There's a gutter to lay the piece of wood into and pour some hot water on it.
Sorry, no pictures of this one... yet.
Each side-piece was soaked in water overnight and then laid into the gutter. Some hot boiling water was poured into the gutter and the piece was left there to heat up for a few minutes. Then the side-piece was clamped to the body shape jig very carefully and quickly, because the wood cools down very rapidly. The side-pieces was removed from the jig the next day and the top and bottom blocks, kerfings and side struts glued in place.
Now the top needs to be fitted to the sides, the bracings that reach all the way to the sides was tapered and grooves filed into the side kerfings where the bracings touch the sides. Paint tape was applied in layers on the tops top-side to prevent any marks and scratches from the clamps. Once the top was glued the same procedure was done to the back. Unfortunately I forgot to take a picture of the "Deluxe's" x-bracing before I glued the back on it... Shit happens.
So now the body was in one piece and it was time to start routing out the rebates on the edges of the tops and backs for the bindings. I used CA glue to attach them using alot of tape to keep it all in place until the glue had cured. ABS plastic bindings, dark brown tortoise imitation for the "standard" version. On the "deluxe" mother-of-pearl with a thin abalone binding on the inside, to add some contrast between the light spruce and the mother-of-pearl.
Next the necks; a 3-piece maple for the "standard" model and iroko with maple stringers for the "deluxe" version. A neck block was glued together and then the pieces for the neck heel and head was cut out and then glued together again, to form the neck heel and angeled head. A lot of sawing, planning shaving and god nows what all different methods I used to carve the necks into shape. An electric file is a very effective tool for shaping, once you're careful.
Another crucial part of a guitars construction is the method of attaching the neck to the body. A lot of different solutions has been used for this and if it's not at least a near-perfect joint it won't stand the test of time that will be put on it by the strings tension. I decided to use a simple yet strong joint, the mortise and tenon backed up by 2 screws screwed through the top-block into the neck heel for extra stability and strength.
So what's left? The fretboards.
I had a fairly nice piece of apple that I had been dried up and prepped for this. So that would be used on the "prototype" version, while a short piece of bishopwood (that was too short to be used for a bass) was selected and prepped for the "deluxe" version. Planned out a blank, cut the fretslots, cut and planned it into final shape and side dots and fretmarkers installed.
Time for some fret-dressing. I find it a lot more easy to glue the frets in place if the fretboard is yet to be glued in place. Much easier to glue, file, level, and crown them if you can move and clamp the whole fretboard around with no effort.
The frets glued, dressed and leveled it was to time to glue the fretboard in place and once the glue had cured overnight some cleanup, filing and sanding was done to get a nice feel to the neck and fretboard.
So now it was time to start making the bridge and nuts, on the "protoype" I had to glue the nut in place first so that I would get a reasonable accurate measurement to locate the exact position of the bridge. On the "deluxe" model this wasn't that crusial, because this type of bridge is not supposed to be glued to the top.
Tuners, nuts, bridges and the string-holder on the "deluxe" mounted on and that magical moment when you hear the first string vibrating on the instrument was at hand, while installing the first strings.
All strings on and a lot of hours spent on filing the bridges and nut slots to get a somewhat correct string height.
Once all the small adjustments and everything was set, all the hardware was removed and it was time for the finishing.
On the "prototype" I first put two layers of knotting laquer diluted 50/50 with thinner and on top of that 3 layers of Osmo Color tree-wax, which I had used before on my fretless bass "Faith" with satisfacting results. On the "deluxe" I had to put 4 layers of knotting laquer/thinner on the sides, back and neck, since the iroko wood is a fairly open-grained wood.
On the "Deluxe" I installed a piezo transducer, the Shadow SH B1 which is originally intended for banjo, but is the only model Shadow manufactures that fits a half-acoustic jazz guitar bridge.
Of course a pickup needs a preamp, so I got this Artec APC with Bass, Treble, Volume controls.
The sound is a bit different on the two. The prototype has a very open and sophisticated sound to it, while it does sound more like a 12-string acoustic guitar than a mandolin.
The "deluxe" on the other hand is fairly subtle and low in sound volume, the sound is more like a 12-string acoustic on the "deluxe" than on the "prototype", might be due to the more sturdy x-bracing.
The "Deluxe" - Acoustic
The "Deluxe" - Electric
However, they both sound in my opinion too much like a 12-string acoustic guitar, I would have liked a bit more of the mandolin sound on both of them.
Very inspiring and educational builds, I learned and did a lot of woodworking that I had never done before...
"Use the talents you possess,