Thursday, September 22, 2011

little arches

The back plate here is getting its final scraping to bring it to my desired thickness. This process was pretty much done before jointing, but a further millimetre or so was removed, first with a toothed blade in a small plane, then with the scraper.
Here the concave workboard for supporting the belly while attaching its struts is in the first stages of being carved. First a template of the desired long arch was made, then a plane was used to create that arch on the plywood. The next shot shows the development of the shape with a small flat plane working mainly at right angles to the centre line to create the cross arched profiles. For the back, the maximum convexity of the plate is only about 3mm. The belly and the back each have their own workboard. A template was made for a major cross arch as well as the long one, just to make sure the shapes were true...the rest was done by feel.
 Some luthiers use a developed radius as the basis of the curved back and belly and there is a lot to be said for the thinking behind that, but I've found great pleasure in looking at and making arches for years now, and I've never found a pure geometric shape to look or perform as well as more complex and perhaps more organic curves and combinations of my arches will look a little less rigid, and a bit more like a hung chain than the surface section of a sphere. The centre of effort on the plate will have an unequal relationship to the various edges, so in my thinking, it should neither be central nor uniform in all directions.

The centre strip that reinforces the spine is of spruce here, with the grain going across the back. Here it is being cut away to fit the cross braces that will run at right angles to the centreline.


  1. As a luthier, how important is your hearing? Do you sense the instrument quality as you build or is building purely a mechanical construction process? Would you, for example, make changes at this stage based on the tonal qualities of the material?

  2. One of my teachers was almost purely mechanical and I've worked through much of what he taught me because it isn't likely that you'll ever develop judgement or feel or intuition if you just work to a ruler. And his instruments were articles of precision but he never developed a great sound. So first I try to notice what feels right (in the loose vicinity of standard measurements), record the data about that, and then trust my judgement until I can hear the results.
    But with a guitar back it is much less important to hear it at this stage because it doesn't contribute anywhere near what a violin back does (dynamically). But it does make a difference, and I've left this piece a little thicker in some places. The belly will be more complex if I'm to make a nice one. With a violin I'd not only tune both plates, I'd tune them to a specific relationship to each other, but that wouldn't work with a guitar because the back plays a completely different role.

    I guess the short answer is that millions of good guitars are made without any consideration of the sound of their components, but people interested both in craft and sound will try to increase their sensitivity in every decision they make that relates dimension to vibration.