Erik's Hjørne: SOUNDBOARD BRACING

INITIAL PREPARATION

Before any of the grafts could go on I traced the whole bracing lay-out onto the top very lightly with a soft pencil using the soundhole center and glue seam as reference points. Once that was done I cut the soundhole with my little Dremel router and a 1/16" carbide downcut spiral bit.

Before cutting the hole, I lined the bottom of the circlecutter attachment with cellotape to prevent the smudging I got when the rosette channels were done. The hole was cut it in two goes. First a little more than halfway down with the rosette facing up, then a second run with the soundboard flipped over with the rosette facing down. This was done to minimize potential tear out.

I also made clamping cauls out of 1/8" maple for all the braces and grafts.

GLUING THE UPPER FINGERBOARD GRAFT - FITTING THE SOUNDBOARD TO THE NECK
As I mentioned in the previous post, the final fitting of the soundboard to the rebate on the neck had to be done on the upper fingerboard graft, so that one went on first. In order to keep things aligned I clamped the adjacent transverse brace in place as a reference to but the graft up against. The bottom of the brace was covered with non stick cellotape to prevent the glue from the graft to adhere to it. Having the brace in place also helped preventing the graft sliding around in the wet glue. The squeezed out glue was cleaned up with a chisel.

When the glue had dried, the top of the soundboard was cut down to the template line with a saw and trimmed to fit with a plane on the shootingboard. As the graft was slightly wider than the neck, little notches were made at the end of the graft to allow for the sided. Likewise, about 3/16" of the lining on each side of the neck was pared down flush to the rebate.

When I did the clamping cauls for the braces, I also made a 'slope', a thin piece of maple tapering in thickness from 3.0mm to 1.5mm, that eventually will be stuck onto the solera to set the neck angle.

This slope was used as a guide for planing a slight taper into the fingerboard graft. I knew that the depth of the soundboard rebate was about 3.6mm, matching the desired thickness of the soundboard and graft at the 12th fret. Getting the right taper and thickness was then simply a matter of calculating where to place the slope on the soundboard and plane away until the correct thickness was achieved. However, I left it slightly proud to allow for some final sanding.

GLUING THE SOUNDHOLE DOUGHNUT
Next up was the soundhole doughnut. This was glued on in a similar fashion to the fingerboard grafts, thus with the two lower transverse braces as guides.

PREPARING THE TRANSVERSE BRACE APERTURE GRAFTS
One thing that I have chosen to modify from the original plan is adding little 0.5mm flat graft under the aperture of the three transverse braces. This is something that Jeffrey Elliott, who I loosely modeled the bracing pattern after, does. These were fabricated from soundboard scrap by planing an oversized piece down with my jack plane. They ended up a little thicker, about 0.58mm, but I figured that was close enough.

Once the stock was thicknessed, three individual graft strips were cut with an Exacto knife and trued on the shooting board until the strips were the right width, each matching their mating transverse brace. This was a fiddly and floppy affair and I had to clamp a little improvised fence on the shooting board to butt the graft strips up against while holding them down with one of the clamping cauls I made for the braces, to keep them straight in place.

Last, the grafts were cut a little proud of their intended length with a chisel. The final trimming will be done once the transverse braces are ready to be glued on.

GLUING THE TRANSVERSE BRACE APERTURE GRAFTS
For this, I wrapped three of the fan brace cauls in cellotape, marked their centers and stuck the grafts onto them with double sided sticky tape, using the already made transverse brace apertures as reference, keeping the grafts straight and flush to one side of the caul. I also placed a little, equally thin shim in the middle of the caul to support a go-bar rod.

When it came to the actual gluing, the upper fingerboard graft and rosette graft were used as guides to butt the cauls up against. First a go-bar rod was added to the center of the caul to hold it firmly in place. Two go-bars were then used added to each graft.

The four top aperture grafts were all glued on flat, while the two lower grafts were done together with the bridge graft on a the 25' radius disc.

GLUING THE BRIDGE GRAFT
This graft was originally done back in July together with the soundhole doughnut and the fingerboard grafts. However, when I revisited the soundboard thickness and thinned it further than I initially intended to, I also started to wonder if 2mm wasn't on the thick side for the bridge graft.

My Israeli luthier buddy, who got me onto the soundboard deflection testing, sent me an article about the Dutch born luthier living in Granada called Rene Baarslag. I the article Baarslag explains how he goes about the thinning his bridge graft, which is about 1mm thick and feathered to nothing at each end.

I have read about other notable luthiers, Romanillos being one of them, speculating about the need for such a graft in the first place. Torres didn't use them and neither has many other world renowned builders that followed in his footsteps.

Rightly or wrongly, I decided to thin my bridge graft to 1mm, flat across the entire length, and with that also making some equally thin spacers for when the fans will be notch. More about that when the fans are going on.

Last the bridge graft and the lower transverse brace aperture grafts went on. This was all done on the 25' radius dish. The bridge graft was the only graft that went on 'freehand' without any reference points to hold it up against. Needless to say that I was a little nervous about it. I applied a modest film of glue on pressed the graft down on the soundboard with my hands. A little sliding did happen initially but eventually the glue started to grip and go-bars were added one at the time starting from the center of the graft and working my way outwards in both direction, slowly letting the glue set for a little before adding another. Once the glue had dried a little the squeeze out was carefully cleaned up with a chisel.

A COUPLE OF NOTES
This is the first time I use a go-bar deck as a clamping device and I must confess that I love it. I don't know how it would have been in comparison to use regular clamps, but the go-bar was a breeze to use - efficient and precise.

Prior to gluing I used a little plumb to mark the underside of the go-bar clamp to roughly know where to put the go-bar rods. This made for a nice, straight downward clamping pressure that also minimized the chance for sliding before the glue was gripping.

TRACING THE BRACING PATTERN