an up and coming guitarist\musician that i know through one of my guitar instructors commissioned me to build an 8 string nylon crossover. i worked out a design based on one of the nearly classical sized guitar body shapes. the guitar will be a venetian cutaway with a 14 fret body join. i am going to use a 660 mm scale to push the saddle down toward the center of the lower bout as i usually build this with a 12 fret body join. the guitar will be falcate braced with a live back.
the back and sides are build from some wild bocote i bought on the olf. the top is an amazing piece of sitka spruce i have. it tap rings clearly for over 6 seconds. the plate would start ringing just running a finger on it.
these plates once sanded to remove the saw cuts 2.6 mm were close to on the edge of being too thin. i tried to use tap tones to get the target thickness but was having trouble reading coherent resonances. so i measured the long gran and cross grain young's modulus using a deflection jig. using those values i came up with a good target thickness. in both cases i used equations from the gore\gilet books.
i joined the plates and decided to stabilize them. a wash coat of naptha showed areas in the figure where the naptha could seep through. i did several applications of thin ca until i thought that the figured areas were filled and stable.
i use tap tones to determine the young's modulus of the top wood and it target thickness.
i joined the two top plates
i pull some less funky bocote from my stash to use for the sides. i had some that was a good color match and i had less fear of bending it.
the normal side bent with no issues so i decided to attack the cutaway side.
i thinned the upper bout just past the waist to the end to .070" . i also sprayed the side with super soft 2 and let it sit overnight.
i bent is a side bender with a cutaway attachment. i am always careful to hold the cutaway press up. i once had it fall and snap a bunch of bindings i was going to bend. also while the wood is heating i am warming the underside of the cutaway. i really want to be able to make the tight bends.
no loud cracks!
amazingly a clean bend :)
so i glued on a tail block and started to make braces and the heel block.
march 5th 2018
while waiting for some bindings on the classical guitar i have made a bit of progress on the 8 string.
i decided on a pretty simple rosette using a rope purfling and a wood ring made from a cut off from the back. to try to clean up the edges a bit i used an lmi rosette circle cutter to mark out the inside and the outside on the rosette. i also scored the sound hole as well.
to install the rosette i first route channels for the inside an outside bindings. in this case the purfling strip and a black fiber strip was exactly 1/8". so i cut the outside channel on the top. keeping the same router setup made a channel on my wood ring blank and then i make the side channel on the top and also transfer the router without changing the settings to the wood blank.
the fit was so tight i decided to install the rope purfling and fiber strip and then just wick in thin ca. to avoid disaster i carefully sealed the channels with [url]http://www.shellacfinishes.com[/url] seal-lac. i would have used shellac, but the seal-lac was out on the counter.
not shown is i bent the rope purfling on a hot bending iron to close to the circle shape. i worked my way around using a 1/4" steel pin to push in the binding. the fiber is so thin, i would guide it into the channel and then push in the rope purfling.
i also installed the inside ring and leveled them to the top. the ring was sized when i cut the channels in the top, so i run it upside down through the drum sander until the ring drops out. looks like a good fit.
with the router sill set for the correct depth i routed out the inside of the rosette. i just start in the middle of the channel and work my way to the purflings until the bit just kisses the inside fiber ring and cleans it.
then i just dropped in the ring and flooded the rosette with thin ca.
it came out ok.
i also braced the back using back stock that i made earlier this year. it is just dimensioned brace stock that i run through a 22.5 degree router bit to make a house shape.
first i needed to install the back strip and prepare it for the braces. i will let the pictures do the talking.
i use a 10' radius for the back. as it is pretty tight i mark the radius on the braces, get very close with a plane and clean them up on a radiused sanding jig i made.
i used a gobar deck with the back on a radius dish to glue on the braces. of note the i made the gluing cauls for the shaped braces by gluing two small cutoffs of the brace stock together at their base. perfect fit!
a second glue up for the radial braces (i only made so many cauls)
my handy brace end carving template sized just right for the brace ends allow me to use a chisel to safely care all of the braces in short order.