Tuesday, November 23, 2010

Closing the Box

Here we have the finished interior. In this instrument I've used "tenelones", or individual glue blocks, to secure the top to the sides. This is a technique borrowed from traditional Spanish practice which works well when a "solera" or dished workboard is used. In my experience there is also a palpable sonic difference in guitars constructed this way vs. the use of continuous kerfed lining. It's not so much that the voice is different, but there seems to be an immediacy to the sound.
In any case, I've used the kerfed lining on the back. This is Spanish cedar, by the way. It costs a little more, but it imparts the most wonderful aroma when one holds one's nose up to the soundhole in search of a lost plectrum.
I've doubled up the tentelones in the lower bout where I intend to install a wide chamfer for forearm comfort.
I'm trying something different in this guitar, using douglas fir for the top and bottom blocks. I got the idea from watching Robert Bennedetto's archtop construction video. I was surprised to find that he often uses spruce for his blocks. Since I had appropriately sized offcuts, I decided to give them a go. For my steel stringed instruments I've settled on a bolt-on neck attachment system. I've tried dovetails, straight tenons, and various bolt configurations. I like to make things easy for future repairs.
There are a number of different ways to close up the box. I often use rope. In some cases I've used go-bars. Today I had my box of spool clamps handy.
Spool clamps are a holdover from violin construction. They're a low-tech solution. They're also indispensable for repair work if one is trying to fix cracks in the sides, or if you've removed a top or back for interior repairs. At the top of the upper bout you can see a brightly coloured smear. A hairline fracture occurred during bending, which has been stabilized with thin superglue.
I suppose the alternative would be small quick-grip trigger clamps, but I'd need $1000 worth. I made these up from theaded rod and closet pole for less than a dollar apiece. They provide just the right pressure. A slightly oversize through-hole means they can pivot to accommodate the back arching. Cork lined surfaces prevent marring.
Front view. This illustrates a subtle little thing I've learned through experience. I've left the soundhole rough, and won't complete it until just before the finishing process. This ensures it will be clean, and any little dings or divots incurred via clamping the fingerboard in place or fretting will be sanded away.

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