Erik's Hjørne: FITTING THE SOUNDBOARD

We have had quite a bit of rain here in Southern California lately, a lot more than average. This had bumped the humidity up to unacceptable levels for this crucial part of the building. The two hygrometers in my garage seems less helpful than I would like them to be, displaying erratic measurements that are in sync sometimes and more than 25% apart other times. Confused, well I am.

Nevertheless I felt it would be best to stay cautious and wait until the rain has settled, and so the soundboard was put to rest in it's protective and comfy sleeping bag - a black bin liner, while I was monitoring our local weather forecast closely on weather.com, that even show an hourly humidity forecast. I waited until weather.com and my own two hygrometers were more or less in line around 50% RH before proceeding.

MARKING THE LININGS
This didn't go as well as I hoped. First I laid the top on the assembly, only holding it down with one hand while trying to mark it with the other. But I struggled with this as I had a hard time keeping the top in place. It kept sliding around a little, making the whole procedure obsolete.

I decided to try and clamp the top to the end block and have that as a reference point. This made everything a lot easier to control. I placed a small engineering square on the neck and used that to butt the soundboard up against, flush with the rebate on the neck and right along the middle axis.

However, I later realized that this too was a flawed approach. Clamping the soundboard to the end block made it bend a little and pulling it away from the neck, 1mm or so. I only realized this when the notches had already been cut in the linings and a test fit was done. I had to widen all the notches to accommodate for this inaccuracy. Not a big deal, but a better way to do this would probably have been to clamp the soundboard to the heel block with a 15mm shim, the same height as the transverse braces, keeping the soundboard evenly suspended above the rim.

The linings were marked with a scalpel, first on the top using the transverse braces as guides, then on the sides with the aid of a small square.

CUTTING THE NOTCHES
I cut the linings right on the inside of the markings with a small razor saw and the waste was cleared a 1/4" paring chisel. Once the major part of the waste had gone, I had to widen the notches a little more to fit the transverse braces. This was quite delicate work, especially in the upper bout where the notches were quite skewed. Thin slivers had to be taken off little by little in order to prevent the linings from tearing. The correction for the inaccurate marking mentioned above was also done this way.

The ends of the transverse braces also had to be fitted a little as they were sitting a little to tight up against the sides. This too was done in thin slivers with a chisel.

PREPPING THE BRACES FOR THE FEET
Quite often brace feet are just a little piece of wood glued to the sides right on top of the braces. But, with a rectangular cross section this means that they don't fit the braces - the corners will 'stick' out. For all practical purposes this doesn't really matter and no one will probably ever see it, but as a kind of an exercise I wanted to try and see if I could cut them in a diamond cross section and fit them in little notches on the brace ends, so their sides would run flush with the braces while the ends would follow the tangent of the sides. This meant the brace end notches and the corresponding foot cross section had to be cut and fitted individually.

With the assembly mounted in place on top of the soundboard, I marked the braces approximately at the width of the linings. On the two upper braces I used a little piece of spruce scrap that was held against the sides. Holding it with its middle over the braces, I figured that it was close enough to being at the right angle of the sides tangent. The lower brace was marked using a sliding bevel set by eye.

The notches were cut with a razor saw. The saw was fitted with a little spruce stop clamped to the saw blade with two spring clamps and set to a 2mm deep cut. The waste was pared away with a 1/4" chisel.

At this point I also roughed out the feet from scrap spruce planed into a rectangular cross section, the same thickness as their corresponding braces. Then, one side was planed into bevel. Once it matched the notches on it corresponding brace, it was stuck to the bench with double sided sticky tape, with the bevel facing down, and the opposite bevel was planed, leaving them with a slightly oversized diamond shaped cross section.

The final making and fitting of the feet was left until after the soundboard was glued onto the rim.

THE SOLERA, THE CORK SHIM AND SLOPING NECK SHIM
In order to make room for the soundboard dome, I made a cork shim out of 1/8" cork glued to some thin cardboard. I cut the cork so there was an overhang of about 2mm on either side of the rim including linings.

A larger pad was glued to the upper part to support the clamping pressure from the soundhole clamp on the two upper transverse braces. Likewise, a smaller pad was added below the soundhole to support the pressure on the lower transverse brace. As this brace is arched, the cork was thinned to about 2mm, or about 5/64".

As the body will be suspended by the cork shim, I had to make a shim for the neck as well. This was done in maple tapering from 3.0mm to 1.5mm over a length of 29cm. I did however, cut it slightly shorter to give way for the spool clamps near the neck, that will be needed for when the back is glued to the assembly. As the cork was stuck to thick paper I had to do the same with the slope. I suppose that I could have just made it that little bit thicker, but I didn't. Oh, well.

DRYFITTING
Finally a dry fit was performed. First I had to take half of the solera support feet off in order to get the oversized soundboard in place. Once it was in, the feet was put back on again using the template to place them accurately. The soundboard was held in place by the soundhole clamp and the side/neck assembly was placed on top. It was an almost a religious experience to see it all come together.

Eight spool clamps were inserted into the holes around the periphery of the solera at an even spacing, ready to receive and clamp the rim down.

GLUING IT ALL TOGETHER
Once everything was lined up, the side/neck assembly was taken off and a modest film of glued was added to the edge of the rim, head and end block and placed back on top of the soundboard again. I used the eight spool clamps already inserted to clamp it down along the sides and big deep reach Bessey clamps and cauls for the heel and end block. The neck was held in alignment with a small bar clamp.

I had a little bit of squeezed out glue to clean up, particularly around the heel and end block. This was done with a spruce chisel made for this purpose. It was the first time I used wood to clean up squeezed out glue, but it worked really well, and I didn't have to be so careful not to mare the surfaces. Spruce chisels can also be made in all shapes and sizes in no time, making them very suitable for this particular job where accessibility was an issue.

MAKING AND FITTING THE BRACES FEET
Initially each roughed out brace foot piece was cut into two 2" long feet, one for each side of the individual braces, but as I started to dry fit them, I shortened the feet for the two upper transverse braces, about 1/8" and 1/4" respectively, as the width of the guitar rim decreased steadily from the waist towards the neck, and I wanted to leave an equal gap between the top of the feet and the lining above them.

A bevel was planed lengthwise, tapering the feet towards the top and the gluing surface was sanded to fit the curvature of the rim.

Most of this final fitting was done by eye. I had to redo some of the feet from scratch mostly because they got planed or sanded too much and weren't fitting snugly in the notches anymore, while I accidentally tapered the wrong face of others. But, eventually they all fitted fairly well where they were supposed to.

The feet were glued in and clamped to the sides with spring clamps. I tried to angle the clamps so any sliding would go downwards locking the feet in place. A trick from Cumpiano's book. I also fabricated small cauls for the feet, mostly to protect the feet from being marred by the clamps.

TRIMMING SOUNDBOARD OVERHANG
I clamped the guitar neck in the patternmakers vise and went at it with a 1/2" chisel, first in rather broad strokes, then in finer ones as I worked my way down towards the sides. It went relatively quickly.

A spokeshave was used for some of the finishing work. I set the blade slightly skewed, fully recessed at the side that was on top of the rim, whereas the other side was set to cut. This way the danger of the spokeshave digging into the rim was minimized, while the depth of the cut could be adjusted from a more aggressive cut to a very fine one, by holding the shave further over the rim or not.

LAST NOTE
I am was really pleased with the fit between the rim and soundboard. Both the beveled linings and endblock, as well as the slightly sloped neck rebate seemed to fit perfectly, with no visible gaps to be seen at all, inside and outside the rim, both during dry fitting and gluing. I don't know how it would have looked, had I not gone through the trouble of bevling the linings around the lower bout, but this appeared to work very well.

MARKING LINING NOTCHES