Acoustic Guitar Construction

I finished closing the box on the classical guitar today. From the last post I had to route out the rebates for the back braces and sort of clean things up. Another change I made at the last minute was to rework my solera so that the neck will have a slight forward tilt. The nut location on the neck should be about 2 mm higher than the plane of the guitar. I was not going to do this and rework the fret board instead to get my geometry but most of the higher end classical guitar luthiers do it so I decided to do so as well. I am waiting for the glue up of the back to cure before I know how it will work.

The pictures below show my setup for routing the rebates for the braces and how I set the depth. I mostly carve the ends very close to 1/8" but setting the depth of the bit on my baby die grinder right on the brace allows me to have really tight joints.

The back matched the profile really well you can see that it conforms nicely to 15' radius, clamping just the heel and the end block. Also when I went to glue the back on I got really good squeeze out after just a few clamps were on, although ultimately I did not skimp on the number of clamps.

Like Christmas morning I could only sleep till 4:30! I pulled the clamps off of the guitar and trimmed the excess every where except near the neck and heel. From my initial measurements everything is where I wanted it. On to the binding and purflings. The only new thing I am going to do is to not taking the binding all the way around on the heel end of the back. Instead I am going to take the binding just past the edge of the heel so that it looks to be inset into the heel cap extension I left on the back. If I can not make it look clean I will go ahead and cut it through and bind it like I normally do. Having the neck already on makes this whole operation a lot harder. Extending the back through the heal cap assures that I have a lot of hand tool work to bind the back. I will take pictures as I go for the good or the bad.

Some good work there, John.

That looks so sweet with the sapwood center...I love it.

Kevin

I have not posted in a bit as I have had a hectic schedule having to travel to Beijing to give a talk. But any way in the mean time, I did install the binding and the purflings, not without a few issues. Live and learn ...

Working with a classical built with a Spanish neck requires that the area around the neck has to be done by hand with knifes and chisels. I did OK, with the sap wood strip up the center of the back I did not want to cut the binding channel where the back wood became the heal cap. Rather I cut it in a bit much like a violin back. To accomplish this I drew out the cut I wanted with a scalpel and treated it a bit like an inlay using a mini mill grinder. The tip on the bit only allowed me to go 1/16 inch or so deep but I was able to get the start on the channels I wanted and used a 2mm chisel for the remainder. Normally I would use a razor saw and just cut across to open the channel. On the top I just used a scalpel and a 2mm chisel to cut the channel under the fret board.

The two real problems I had:

When routing the back I was a little loose where I started a cut and tore out a hunk of back almost to the end of the kerfed linings. I cleaned up the tearout and carved a matching patch from a cutoff that was right next to the tear out ( save those cut offs) See if you can find it. Once you see it, it does not go away, it does not look too bad.

The other is I decided that a lining installed on the back was too dark and not a match for its neighbor. This was the only binding on the guitar so I removed the it. Unfortunately I goofed up the miter on the end strip. I was trying to patch a bit of the purfling when I decided to chisel out more of the binding to make a bigger patch when it dawned on me that it was just as easy to remove the whole binding. I have a 1mm chisel that I made out of a 2mm chisel. After using a scalpel to separate the binding from the rims it was easy to just chisel out the binding cleanly and install a new one.

Give that this is a classical I took the time to use a spectrum analyzer to get the resonance frequencies close before I routed the binding. Now they are high but with the bridge glued on the first resonance should drop to about 100 and the main resonance should be about 102 Hz. That is my target anyway. I also have mapped the entire top with a magic-probe.

The bindings are Australian Blackwood with bwb side purflings. I have a brown white brown purfling for the top to match the rosette.












On to finishing the neck and fret board!

We've learned to expect very fine work from you, John, and this is no exception.

May I ask what the talk was about in China? Intriguing!!

deadedith wrote:...
May I ask what the talk was about in China? Intriguing!!

I gave a talk about the value of some specific computer management standards to Chinese manufactures at the ceremonial opening of a china chapter of an international standards body. The whole thing was weird as usually I am the technical guy hiding in the background, but here I was the VIP and had to have special room meetings with high government bureaucrats.