Soundboard: Glue-up

Today I completed the process of planing my boards down to about 3.5 mm. After laying the boards edge-to-edge, I chose to rejoint two edges just to clean them up. Then I trimmed a bit from the front of each board, as the planer had sniped each one a bit at the end of each planing pass.

Next I brought out the instrument, which has been resting in a corner of the workroom since the framing was finished in early November, and started laying out the soundboard wood in sequence on top of the liners. I clamped the leftmost board in place along the spine, keeping the closest edge about 1/4" in front of the upper belly rail, and marked the final length of the board about 1" beyond the far end of the liners. Each board received the same treatment, and as each was trimmed it was replaced back onto the instrument in sequence. Here's a picture of the process:


I'll use the off-cuts to make up a cosmetic veneer for the wrestplank surface.

Originally my plan was to make the soundboard long enough that the front portion would be cut off and made into the wrestplank veneer. Unfortunately, several of my boards have defects close to the far end, and if I had pulled them all forward so that they were flush with the front end of the wrestplank, these defects would have ended up on the finished soundboard. I'd rather not have knots and splits on my soundboard. By keeping the front edge of the boards almost flush with the upper belly rail, the defects end up beyond the perimeter of the instrument, where they can safely be cut out.

At last the time came to actually start gluing the boards edge-to-edge. I made up a gluing platform consisting of an 8-foot section of plywood, two 8-foot long pine boards, clamps, wedges and a bunch of bricks.


The bricks got wrapped in paper because they like to shed red dust all over the place.

One pine board was clamped parallel to the long edge of the plywood. A sheet of wax paper was laid down and two soundboard planks were placed on top. A long skinny off-cut of soundboard wood was placed along the edge of the second plank, and the second pine board was clamped about an inch away from this. Numerous pairs of wedges were inserted between the pine board and the off-cut.

The actual glue-up is quite simple. Two soundboard planks are folded together face-to-face to expose the mating edges and a bead of fish glue is squeezed on and brushed out. After replacing these planks on the plywood sheet, the wedges are squeezed together, which presses the two planks together, the off-cut serving to protect the outside edge from being indented by the wedges. Bricks are placed on top to keep everything from buckling upwards as the pressure increases. The set-up looks like this:


The "gift-wrapped" bricks ended up that way because they were still shedding dust.

With this set-up, I can glue up several pairs of boards each day. There are 8 boards in total, and I'll soon be able to glue 2 pairs of boards together, and so on until the entire soundboard is complete.

This method is similar to what harpsichord makers did centuries ago in gluing up their soundboards, according to surviving accounts.