estebanana -> RE: Question About bridge torque and dome (Apr. 5 2018 1:15:14)
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Jason, there's no formula. The bridge gets rocked toward the nut lowering the string a tiny bit. How much? Each top is different because the bracing and thickness are different and the inherent stiffness along the grain. The bridge also often takes time to rock forward, it can happen in 15 minutes, 40 days or 15 months....each one is different. One thing you can do is arch your lower transverse brace and little bit, this sets up an adjunct structure to the arch in the form of a rigid curved beam. It helps stiffen the area between the sound hole and bridge. You also have to watch the strength of braces and top thickness between soundhole and bridge. But there's always a trade off, some of the bridge rocking forward is good for flamenco guitars and can be seen on a lot of guitars. Some makers build the rocking motion out of the system by brace and top thickness and others allow it to happen in varying degrees. You just have to decide which style you want to build and how much forward rocking you're willing to allow to the bridge. If it were me, and this is how I figured this out, I made my first guitars heavier than they needed to be and progressively made them lighter. In the beginning I would error on the heavier side and bit more robust and then go lighter over time. But if I were you I would not worry too much about this, because you can plane the finger board to make your set up in the pocket, and then if you have a healthy break angle and potential to adjust saddle, you fix any rocking by set up. Just observe what happens on your guitar and make note of it. Then look at the guitar over time to see if anything changed. --------------------------------------------- If you can look at a lot of nice flamenco guitars or when ever you see a good one, make an accurate wood straight edge or use a metal straight edge. ( wood is more polite if looking at someone else's guitar) Put the straight edge on the top behind the bridge and check the arch of the top. If the strings are on you can pull a thread under the strings and then pull it it taut a few mm's over the top to see the arch in front of the bridge. Some things you may see - Flatter arch under string tension in front of bridge. Then flatter bridge seam at top in front, more curved seam behind bridge. That often indicates a light thin top, light flexible bridge. You also may see bridges that have arch under them, but observe the top dips down between the wing ad the edge of the lower bout. Very likely the top was braced flat and the bridge was curved underneath and the top was pushed up into the bridge when glued on. That's a style of building, some makers do it that way. In other words, instead of the bridge being fitted to a arched top, the top is pressed up into a bridge thats arched on the bottom side. Tops and bridges made that way can often express the depression between bridge wing and lower bout. Anyway, these are just things to look at when examining bridges, the bridge area tells you a lot about how the guitar was made. That and the quality of the top are really the only things that matter much. By quality I don't mean just stellar looking wood....
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