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Yikes! I'm surprised it would die, especially so fast, with such tall and numerous fan braces. Can you take some pictures like this?


That's one of my small classicals, which are 11.3" lower bout width, 25" scale, 5/16" or 8mm string-height-at-bridge (although I just checked and it looks like that one's actually more like 7mm at the moment... it can be varied by adjusting how the strings are tied). The top is engelmann, about 1.7-1.8mm thick if I recall, but down to 1.5mm in one spot. Braced like this:

And using Aquila Ambra 800 strings, which are lighter tension than normal, although I had it strung with regular Ambras for several months and it was about the same deflection. As you can see it certainly isn't flat, but it'll have to go quite a bit further to cause any trouble. The top is quite plush if I push on the bridge.

The fingerboard on yours certainly does look too thick... and it looks like the fret slots are shallow by that shot of the fingerboard end at the soundhole. Didn't I tell you to cut them almost all the way through so you can plane it as needed? And then I did the same thing on my harp guitar and now need to buy the refretting saw from StewMac to deepen the slots so I can thin the board

Oh well, at least now you have a data point in your mental database of what a top feels like when it's too flexible for that much tension at that much height on that long of a span. If I were you, I'd pull the frets and then either get the refretting saw (hey, you could buy one, use it, and then sell it to me ), or just saw through the binding to deepen the slots. Then plane down the fingerboard, possibly tapering the thickness depending on what the neck angle is like, and get that bridge height down. Although if it's only 10mm right now, cutting it to 8 probably isn't going to be a make-it-or-break-it difference, so you might need to go even lower.

Option 2 is to pull the fingerboard, thin it from the back, pull the top, make a new and slightly thicker top, and then put it all back together. That would also give you another chance to flex the current top with your fingers to memorize the stiffness.

But like I said, I'm surprised it would die... with that bracing and that bridge width at such small size, I would have expected it to be too stiff. Has the humidity dropped significantly in the past few days? Does it spring back flat if you take the tension off?

So I have a new plan, sort of. I want to try and keep the top that's on it by fixing the crack and adding another brace or two on the inside for extra support. Then I'll calculate how much to sand off the fretboard to have the same action it has now with a 7.5mm saddle height. Then its off with the fretboard for sanding. Has anyone done this without removing frets? I feel like I'm probably gonna have to take them out unless there's some genius way to keep them in.

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It did spend a couple days in a hot house without ac. And after slacking the strings it does seem to spring back quite a bit. I was hoping to take the fretboard off and sand from the back but now I like the idea of keeping it on and sanding it down from the top since I'll have to take the frets out either way. Do you think I should try lower for the bridge? Maybe 6mm?

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Ok here's the pictures, finally. They're pretty crappy but I was in a hurry. This is with full string tension. They are slackened right now.


DSC_0007 by markpotato, on Flickr


DSC_0006 by markpotato, on Flickr


DSC_0005 by markpotato, on Flickr


DSC_0004 by markpotato, on Flickr

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That definitely does look like over-torque. And indeed way more than I would expect. How much of the bridge area has come unglued? Just the area right by the crack, or can you get a piece of paper under that bass side wing anywhere else? And I assume there's a fan brace under the crack area? Looks like the brace is holding steady, but the bridge wasn't glued to the top wood over it, and the top wood wasn't strong enough to transfer the stress to the brace.

Here's a good test to run... string it up without a saddle and see what happens. If it still over-rotates at that height, you'll definitely need a new top. But if it's ok, then there's hope. Also could make a 7.5mm saddle to test it at that height (even if it's not playable due to the fingerboard)

Hot house without AC doesn't indicate much about RH... could be dry, or could be like here lately, 90 degrees and 60%. But that doesn't look like a humidity crack anyway, being short and peeled open instead of a long, fine line.

More than anything this makes me question why my guitars are still alive. I've been thinking the torque on the bridge was entirely defined by the string height x tension, but maybe the break angle of the strings over the saddle really does increase it, and the lute style tie bridge on mine is what makes the difference. I'll have to ponder some more on that.

Actually, I was expecting a lute style bridge after looking at the pictures on wikipedia, although looking on google image search it does seem like more use a saddle than don't. But since you'll probably need to reglue the bridge anyway due to the area that caused the crack, switching to a saddle-less bridge is an option. It is tricky to get the intonation right, though, due to the string looping under itself making the actual end point of the string a couple mm or so in front of the bridge.

Best of luck with the fixing. Not much fun, but very useful learning experience, not only getting repair practice, but also records of what is "too far". At least IME, the style of "building on the cusp of disaster" really does result in the best sounding instruments, so the more disasters you cause and resolve, the more accurately you can approach the line without stepping over

Only that little spot where the crack is is where the glue didn't hold. Everywhere else looks like it was glued very well, and I don't want to reglue it because I don't think I can get a better joint than I have right now. I have read before that the string break angle is crucial in both structural stability as well as volume, and i have heard that if the angle is too great, you will have issues like this. So i want to fix the top from the inside and add a little support. I dont want to unglue anything unless i really have to.

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