Catastrophic failure - any hope of repair

Construction and repair of Classical Guitar and related instruments
printer2
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Re: Catastophic failure - any hope of repair

Post by printer2 » Fri Mar 08, 2019 2:21 pm

With the thought of the top being toast I would clean up the back of the bridge, the ripped out area of the top. Add individual backing plates on the underside of the top in between the lattice structure using wood jacks at each patch (the top and back of the body as a gobar deck). Put a patch over the bridge area, level and glue on the bridge. But then again my time is free and I have wasted it on lesser things.
Fred

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Beowulf
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Re: Catastophic failure - any hope of repair

Post by Beowulf » Fri Mar 08, 2019 2:44 pm

Looking carefully at the break, I suspect that a number of factors contributed to the bridge tearing off: thin top, scoring of the top (particularly at the front of the bridge), minimal lattice support in the central area of the bridge (which has the greatest pull from the strings) and inadequate gluing to the lattice braces. The fracture point is at the front of the bridge and is totally clean, which suggests that the scoring was much too deep in that area. Once that let go, the rest of the bridge simply tore away raggedly. Under string tension the bridge was pulled up slightly at the back and the weakened area from the scoring at the front acted like a hinge and...whap. If that "hinge" had not been present, one might see a slight hump behind the bridge and a slight hollow in front of the bridge under string tension. I would agree with James...incompetence.
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dougcalton
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Re: Catastophic failure - any hope of repair

Post by dougcalton » Fri Mar 08, 2019 3:51 pm

I understand the conclusion that diagonal scoring was responsible for the triangular sections, but can't imagine why anyone would do that? To make the bridge stick better to the top?
1989 Marin Montero
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Beowulf
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Re: Catastophic failure - any hope of repair

Post by Beowulf » Fri Mar 08, 2019 5:21 pm

It is possible that the triangular sections are a result of the actual "tearing path", rather than diagonal scoring. The bridge may have twisted as it tore off, rather than moving uniformly in the direction of the string tension. So, it started to tear off on one side and then ripped across to the other side as it broke free.
1971 Yamaha GC-10 (Hideyuki Ezaki)
2017 Yamaha GC82S (Akio Naniki/Naohiro Kawashima)

Alan Carruth
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Re: Catastophic failure - any hope of repair

Post by Alan Carruth » Fri Mar 08, 2019 5:34 pm

Those diagonal marks look to me like the places where the lattice braces were glued on. That's natural for that sort of failure. The clean break at the front of the bridge may not be due to deep scoring: I would almost expect that on a thin top anyway once the rear side of the bridge started to go. There's quite a large enough stress riser there to start a fold without scoring.

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James Lister
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Re: Catastophic failure - any hope of repair

Post by James Lister » Fri Mar 08, 2019 5:48 pm

Beowulf wrote:
Fri Mar 08, 2019 5:21 pm
It is possible that the triangular sections are a result of the actual "tearing path", rather than diagonal scoring.
I don't think that's likely - wood doesn't really tear in straight lines diagonally across the grain.
Alan Carruth wrote:
Fri Mar 08, 2019 5:34 pm
Those diagonal marks look to me like the places where the lattice braces were glued on.
If you look closely, the triangular sections of soundboard wood missing from the back edge of the bridge don't line up with the lattice braces.
You could be right about the front edge Alan, but I'd expect at least some splintering outside the bridge outline - and there's none.

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Steve Ganz
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Re: Catastophic failure - any hope of repair

Post by Steve Ganz » Fri Mar 08, 2019 6:25 pm

+1 for James interpretation of what happened. There was a knife or razor used on the top....
Sometimes guitar builders score or crosshatch the underside of the bridge in order to get it to grab the glue. Not on this bridge. Something may have gotten lost in translation and the builder crosshatched the top.
Some builders also finish the guitar then cut through the finish around the bridge with a razor, trying to just cut through the finish. Then scrap of the finish. I could believe this was the intent. (who knows?)
But not on a 1 mm thick top! [/i]
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Re: Catastophic failure - any hope of repair

Post by SteveL123 » Fri Mar 08, 2019 7:17 pm

I'd be interested in the top thickness at the bridge. It'd be easy to measure with the hole.

Make a caliper with a piece of wood by cutting a slot with a saw, widen the slot with a thin sanding board till it fits snug to the top. Measure the caliper gap with thickness gauges.

printer2
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Re: Catastophic failure - any hope of repair

Post by printer2 » Fri Mar 08, 2019 9:40 pm

But is it repairable?
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beanctr
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Re: Catastophic failure - any hope of repair

Post by beanctr » Fri Mar 08, 2019 9:49 pm

Anything is repairable but how much $$ do you want to put into it. New top could be $1,000 plus. R
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James Lister
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Re: Catastophic failure - any hope of repair

Post by James Lister » Fri Mar 08, 2019 11:06 pm

printer2 wrote:
Fri Mar 08, 2019 9:40 pm
But is it repairable?
Definitely not worth trying to repair the top, but maybe worth replacing the whole top. I have a method for doing this that avoids cutting through the fingerboard at the 12th fret. I think I charged about £750 to do this once, so probably worth doing on a $4k guitar, but of course it won't be the same guitar.

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hesson11
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Re: Catastophic failure - any hope of repair

Post by hesson11 » Sat Mar 09, 2019 12:13 am

Have you tried contacting Willie Nelson to see if he'd be interested in buying it? :-)

Seriously, I'm very sorry this happened to you. I've never seen anything quite that bad.
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Re: Catastophic failure - any hope of repair

Post by Philosopherguy » Sat Mar 09, 2019 6:00 am

If you decide it's not worth fixing properly, as an experiment I would be tempted to try to glue that bridge back on exactly as it tore out (not too much cleaning or removing of the wood under the bridge to keep correct height and material to bond to) and add some patches or cleats to the area around the braces underneath where the saddle to keep the top as one unit. You can still see where the braces were touching the top underneath the bridge. Clean that up a little so that glue will stick and clamp it all up with some titebond. Never know, it might survive and sound good again! If it fails again within a few years, you didn't lose much. I have done some crazy repairs to broken guitars that weren't worth fixing over the years that have worked surprisingly well for the cost of glue and some time clamping.

If you decide it's worth fixing correctly, I would just get it fixed instead of wasting time.

Just my opinion... Only you can decide what kind of worth you put on the guitar.

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Keith
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Re: Catastophic failure - any hope of repair

Post by Keith » Sat Mar 09, 2019 3:11 pm

Since the guitar was a lattice built, was the remainder of the guitar (sides and back) built in the style of Smallman (thick/stiff sides and back)? If so, then a question to pose: Would a new top, built in a non-lattice typical thickness, function differently given the thicker/stiffer sides and back? This might be an interesting experiment--half "Smallman" half "Torres" kind of guitar.
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dougcalton
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Re: Catastophic failure - any hope of repair

Post by dougcalton » Sat Mar 09, 2019 4:06 pm

Regarding top thickness, I felt a bit lazy, so used a clamp to rough measure the thickness. Looks to be 1mm.
The back was actually carved from maple (the shop mainly built violins, so that is what they knew). I assume the sides are double laminated, but don't know for sure. Pretty flame maple. Not sure about the experiment. I know a local luthier that would do a standard torres-based top, hopefully cheaper than shipping for a true lattice. Thinking about it. I am confident the bridge can't be glued on - the wood behind where the bridge was is pretty punky and distressed. I don't think there is any integrety left in the soundboard for that area.
1989 Marin Montero
2015 Slavko Mrdalj Lattice Top cedar, double back and sides indian rosewood

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