Soundboard glue-in

An auspicious day: the soundboard was finally glued in.

Earlier I checked the fit of the board to see if the presence of the case walls affected the fit. It seemed fine except the cheek edge felt a bit tight, so I gave that edge a little rub with coarse sandpaper and the fit was good to go.

After taping the edges of the soundboard and the inside edges of the case to protect against glue squeeze-out, generous amounts of fish glue were applied to the liners and the soundboard was set in place. An arrangement of clamps and cauls held the board against the liners and the upper belly rail. I admit that in a perverse kind of way I looked forward to this moment, as I was finally able to use 47 of the 50 F-clamps I bought last summer, plus a bunch of C-clamps.








The instrument is respectfully dedicated to my friendly harpsichord maker, and has been so inscribed on the underside of the soundboard.

A day later, the glue was dry and the clamps came off. I used my block plane to trim the front edge of the soundboard, which overhung the upper belly rail a smidgen along its length.

It should be clear in the photos above that I already trimmed all the overhanging case edges, which were left long as each piece was glued in (see the photo in the previous post for comparison). I taped each joint to protect the wood from scratches, and, using a Japanese-toothed dovetail saw held flat against the case, I sawed off the excess material at each joint. A little sanding smoothed out the cut edge, although I didn't aim to get the joints exactly flush at this point in time.

Case work: Spine

Time for the spine to go on:


Plenty of clamps were needed, and a couple of spring clamps at the tip to clamp the bevel joint (51.5 degrees) together. The spring clamps are kept from sliding off the tip with strips of very coarse sandpaper.

To allow the installation of the registers later on, a small rectangular spine window was cut through the spine in line with the left end of the gap between the wrestplank and the upper belly rail.

Case work: Cheek

Today the cheek was glued on:


It was a lengthy job to fit the cheek to the bentside. Despite the block I clamped to the bentside liner, the treble corner of the bentside did curl inwards a little, so I was forced to sand the bevelled cheek edge (32 degrees) all afternoon until I matched the slightly curved profile of the bentside edge.

The sticks allow clamping pressure to be directed to wrestplank level, as any effort to clamp along the upper edge of the cheek would probably split the case material, which is unsupported above the wrestplank. Similar sticks were temporarily attached to the spine side of the wrestplank supports with double-sided tape, and clamps placed across the instrument squeezed the upper and lower ends of these together.

Case work details

Cutting bevels at the joints between various case parts is a little trickier than it might seem. The Trasuntino has rather sharp corners and the required angles cannot be set directly on most power tools, which only go up to 45 degrees. Such tools are designed to help cut things square, or to make up angles that add up to 90 degrees (two 45-degree miters, for example).

To cut an angle of more than 45 degrees—and all the case bevels, except at the cheek-bentside corner, exceed 45 degrees—I built the following table saw jig, which stands the workpiece up on end instead of flat on the saw table. By changing the orientation with respect to the saw blade, the complementary angle can be cut, which will now be less than 45 degrees.


The jig slides along the saw fence, and the table is tilted to the appropriate cutting angle. A sacrificial piece of plywood keeps the blade from slicing into the jig, and a sample piece of yellow cedar is shown in the proper position.

I'm using a Shopsmith Mark V Model 510 saw system; with suitable accessories it can also operate as a jointer, sander, bandsaw and drill press. It's a good tool, but the tilting table makes angled cuts a bit tricky. Cutting the spine bevel was a real production: my father and I dragged the saw out of the garage onto the driveway so that the 92" long spine wouldn't hit the roof rafters during the cut.

The front edge of the cheek and spine are cut out decoratively on most Italian harpsichords. I glued two additional layers of wood against the inside face of each case piece, making a sandwich of two outer layers of yellow cedar and a thinner middle layer of walnut. The grain of the middle piece is at right angles to the other two. Below, some walnut is glued to the outer layer of cedar:


I made a plywood template from a tracing of the original Trasuntino cheek profile shown on my drawing. When the three-layer sandwich was ready, I traced the template profile onto it in pencil, cut most of the waste out with a jigsaw shy of the line, then attached the template with double-sided tape and ran the whole assembly against a piloted flush-trimming router bit to cut the exact final shape. Below are the spine and cheek cut-outs: the cheek has been sanded thoroughly while the spine is still rough from the router table:


I sharpened some of the corners of the profile on the cheek, which are naturally softened by the round router bit.

It's interesting to note that these layered cutouts not only look good but add strength to an otherwise weak area of the case: the sides are attached only along the baseboard at this point. Many cosmetic elements on Italian instruments turn out to have strengthening properties when one looks more closely at them.

Case work: Tail

After getting the bentside attached, I found I still had time for a little dessert, as it were, so I decided to attach the tail piece next. The only tricky part was to determine the bevel on the tail, which slips in behind the overhanging edge of the bentside. Some trial-and-error cutting eventually determined this to be 57 degrees. I found I also had to cross-cut the tail piece at 1 degree off square before cutting the bevel; otherwise a gap occurred where the two pieces met above the liners. Somehow things ended up slightly out of square, but the slight skew in the cut compensated nicely.

The glueup procedure was largely the same as for the bentside, but much more relaxed and without any bending required. I didn't bother pre-drilling the screw holes before gluing as I did with the bentside, as now there were only half a dozen to deal with compared to the 36 I drilled in the bentside.


The slotted rectangular plywood block is an idea I read about in several sources. I don't know if it has a proper name, but someone unofficially referred to it as a "jamb cleat". The liner and case material slip into the groove, then a couple of wedges are pushed in to provide clamping pressure. I installed one right at the point of the tail, a position that would be hard to clamp any other way:


The screws keep the cleat from sliding off the point as the wedge is forced in.

Case work: Bentside

I suppose I could have done this quite some time ago, but it's finally time to start putting the case together.

The case wood is quartered Alaska yellow cedar in the form of 3 boards 10 feet long, 7.5" wide and 3/16" thick. The latter two dimensions are final, as the boards were milled to my specifications when the original lumber I bought back in September was resawed. All I need to do now is cut the case pieces I need out of these long boards.

I'm starting with the bentside, which I've rough-cut to a length of 190 cm, about 4" more than necessary. Professional harpsichord makers usually miter all the corner joints when making Italian instruments, but frankly I'm too chicken to try this. My plan is to half-lap the joints, which, at each corner, will require one board to be glued on over-length and the mating board bevelled on its edge and glued up against it. Then the excess length on the first board will be cut off and the joint planed and sanded flush. This is slightly less elegant, I admit, but easier, considering that the bentside is a tricky item to deal with.

My bentside starts out as a straight piece of wood: it needs to be muscled into place against the curved side of the instrument and clamped. It's not pre-bent in any way.

Before gluing, I taped off all parts of the instrument that need to stay clear of glue, either for cosmetic reasons or because something else will later be glued to that area. Next, I attached some little blocks along the baseboard with double-sided tape, letting them stick out an inch or two past the edge. These will act as little shelves to keep the bottom of the bentside perfectly aligned with the baseboard edge.


The bentside, cheek and tail pieces are seen above, resting on the framework. Another detail to note is the block clamped to the wrestplank support at the rear left of the picture. This is to keep the part of the bentside above the liners from curling inwards, which I noticed it had a tendency to do during dry clamping runs.

Clamping the bentside is easy up above, since the clamps reach down to the liners, but clamping along the baseboard is difficult: the only way to do it with normal clamps would be to nail a bunch of angled blocks along the spine to help hold a long bar clamp. Instead I've chosen to pre-drill and countersink small holes at 2" intervals, through which I'll drive short #6 flat-headed screws. These will hold the bentside along its bottom, and later a decorative moulding will hide the screws from view.

With my father's help, we glued the bentside on in several steps. Before applying glue, we clamped the entire board on, though not with the full number of clamps we planned to use. Then we unclamped about half of the board at a time, spread glue along the baseboard edge, knees and liners, put the board back, clamped it, and screwed the bottom edge down.


A detail of the block supporting the bentside in the treble:


The treble part of the bentside has the most extreme curvature, and I found that simply clamping it along the liner would not bring the bottom edge in. I was leery of trying to force it into place with screws: the case wood is quartered, which makes it quite likely to split with rough handling. Instead, after one of my dry runs, I screwed four little blocks underneath the baseboard in the treble area, just back from the edge. Then, during glueup, we clamped a long stick to the case right in front of each block, letting it hang down a bit below baseboard level:


A C-clamp squeezed the stick and the little block together. This arrangement was able to bring the bentside bottom edge flush with the baseboard.