Say, what's that glowing box in the corner of the room?
It's actually a low tech kiln powered by a light bulb. Pretty toasty in there, 26 Celsius ( 78 Fahrenheit). Dry too, only 17% humidity.
Open up, and in the inviting orange glow we see a stack of spruce soundboards, waiting their turn. I've done some experimentation and have come to the conclusion that soundboards benefit from this treatment of extreme dryness for about a week. Now, these are "seasoned" boards that have been stored for a decade in normal shop temperatures and humidity (45% in my shop). The internal resins have been solidifying and undergoing chemical transformations and all that good stuff. When put through this treatment, they will diminish slightly when measured across the grain, and don't ever seem to go back to their previous dimension even when brought back to "normal" conditions. I think of this as a little extra insurance in the event that the instrument finds it's way to Arizona or Dubai.
Here's a sample of my raw material. This is very pale Sitka spuce harvested in northern B.C. Sitka seems to exhibit less rosy colouring the farther north it grows. This is nice timber, good and stiff, perfectly quarter sawn, reasonably even grain spacing etc. I must say I hold some contrary opinions regarding soundboard material. I feel luthiers sometimes get caught up in the romance of "boutique"quality wood. We're snobby, and unfortunately we can pass that along to the players. A great soundboard can exhibit some uneven grain, squiggles, colour, or other variations. I care about what the wood says to me musically. Is it stiff and resilient? Does it have a complex musical tone when I tap on it? Judging tonewood on its appearance makes about as much sense as judging a musician's ability on their eye color. I recall seeing a great Christie's catalog cover showing a Guarnieri violin with a big ol' pin knot right behind the bridge. That instrument is valued in the millions. In the same vein, a plastic pitcher from the dollar store will be nice and smooth, perfectly homogeneous and it'll hold water. Given the choice, I'll take the hand-thrown wood fired one with Shoji Hamada's fingerprints marring the surface, thank you.
I'm using what's known as a shooting board here. I've taped the two halves of the top back together in the same orientation they had when growing in the tree - "book matching". My trusty Veritas #5-1/2 junior jack plane makes quick work of straightening the edge for gluing. I try to get the joint to fall between two sets of winter growth lines for a uniform appearance.
Here's my gluing set-up. I have a nice flat melamine faced board with two rows of machine screws along each side. I run these in until the central edges to be glued are about 5/8" (15 mm) off the surface. While learning luthiery with David Freeman at Timeless Instruments we made use of wedges and rope to provide pressure. This works great when using Titebond or other slow curing aliphatic glue. I'm now using a slightly curved board and a couple of clamps. When using hot hide glue this allows me to get things wet, pressed flat, and clamped in seconds without fumbling for the rope.
I start planing things flat using cross-grain strokes. This produces scruffy little shavings. I then turn things sideways and plane with the grain to remove the bulk of the material. (It makes the nice wide curly shavings to enthrall children if one happens to be doing this at a woodworking show.) This is one operation that has become faster over the years! I seem to recall scratching away for the better part of a day on my first guitar top. With a sharp blade and a sense of purpose, I had this lute top thicknessed and scraped in about half an hour.
Lute faces usually don't have a "finish" as such, other than wax. Here's a nice shot of the shimmering surface the plane left behind, and you can see the "silk", the medullary rays which dance in the light like little jewels. For lovers of wood, it doesn't get much better than this.