estebanana -> RE: back doming question from a beginner (Sep. 27 2012 1:20:21)
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I hate to be the turd in the punch bowl, and this is not going to be very diplomatic, but ya'll work too hard. The way to do it with out making a bunch of jigs and stuff on a first guitar is much more fundamental. Of course some people love to make jigs and the jig meisters should jig away. All you have to do to brace a back is get a lath of flexible wood about 1/4" thick and 1" wide and 16" long. Take the brace and lay it flat on it's side. Make a pencil mark on each end about 3mm deep. Lay the brace on a shooting board so it over hangs and then simply plane from end to end to a make along graceful curve. Aim from the middle to the mark on the end. After about four to six passes the brace will be rough curved. Tighten the throat of the plane, pull in the blade, and then pass from end to end to smooth it out. Peter Tsiorba has a curve scraped into the sole of a wooden Japanese plane. All he does is pass the plane over the brace and the curved sole causes it to cut a path and it curves the brace! Magic. Take the back, put some glue on the brace, put the flexible lath under the back, under the brace. Clamp the brace on from the middle moving out to the ends. The lath will create surface tension under the brace which will conform to the brace and support it like a strap. Done. No sand paper, no dishes, no wedges, just four elements: Plane, lath, clamps, skill. You modulate the arch of the back by how you cut each brace. Time a practice tell you how you like it. The one near the heel is shallower, at the waist higher, lower bout is luthiers choice according to how you see curves. To fit the back with a plane, the trick is to ease the ribs sloping down a tiny bit from the peak of the waist. You start a gradual slope up to the tightest curve of the waist right from where the upper bout is widest. Same in the lower bout. A few passes of the plane and it's done. This allows the ribs to reach up and meet the back in the waist where the back is higher up, but still allows a flat tapered plane form heel to tail. Another trick is to chamfer the outside edge of the ribs with pass of the plane, because you're going to cut a binding channel there and the outer edge of the rib does not have to get in the way of the back touching the liner. All you have to do is concentrate on making a seam between the back and the liner, the ribs get cut out anyway for binding. Fitting a back with a plane is easy, the dish and the ensuing warped or wavy looking profile is considered an aberration to the classic design, in many builders opinions. After this most straight forward way there are several ways to get more complicated, and perhaps not even faster. But if you practice the most basic way first you learn a lot more in my opinion, because you deal with the very essential problems and not muddle your thinking or eye-hand work with extra props on the stage. [:D] There is nothing "hit and miss" about it. It's acquired skill and to dismiss classic tradition and skill for tricks with jigs is ridiculous. Jigs come after skill and the most elemental ways to doing it because to take it in the opposite order waters down the art and logic of the Spanish design. Sorry it's not politically correct, but that is my firmly held conviction.
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