Catastrophic failure - any hope of repair

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

Post by Chris Sobel » Sun Mar 10, 2019 9:20 pm

Les Backshall wrote:
Fri Mar 08, 2019 12:41 pm
dougcalton wrote:
Fri Mar 08, 2019 11:49 am
I think I'll ask a local luthier to see if he can determine if the top was glued using hide glue. If not, discussion of replacing the top would be moot. Thanks for all the responses!
I've replaced a couple of tops that were glued with Titebond - it's not difficult. There are couple of videos on youtube showing how it's done.
Les
Agreed. I’ve also replaced tops with mystery glues that were more permanent than titebond. It’s just more of a chore. Hide glue isn’t a magic potion that makes things easy to repair... just easier than the alternatives!
CE Sobel Guitars

Stephen Faulk
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Re: Catastrophic failure - any hope of repair

Post by Stephen Faulk » Mon Mar 11, 2019 1:59 pm

Just for fun, have someone try gluing the bridge back on with cleats fit between the lattice. Put a light in side the guitar and trace the lattice pattern with the bridge laying on the hole.

Then have them fit patches of thin spruce into the squares of open top under the bridge and glue them in with a caul. Then glue the bridge to the new substrate under the bridge and try to consolidate all that loose wood and splinter under the bridge. It will be a shoemakers job, but you never know it might last another ten years if done well.

The diagonal scoring and scoring around the bridge looks like a major oversight on the part of the makers. Bridges don't need scoring on either the bridge or the top.
Patience at the bending iron pays in rounded dividends!

Alan Carruth
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Re: Catastrophic failure - any hope of repair

Post by Alan Carruth » Mon Mar 11, 2019 2:49 pm

It used to be thought that scoring or 'toothing' the surface to be glued made the joint stronger. Partly it was done to 'give the glue someplace to go' when the joint was clamped, and partly there was a belief that most of the strength of the glue line is mechanical, so having more glue in the joint made it stronger. It turns out that a major part of the strength of a glue line (and just how much is debated...) is chemical. In that model what you want is the thinnest possible glue line, with as much wood as close to touching across the joint as you can get. Toothing actually makes the joint weaker, since it reduces the close fitting area of of the glue line, and the thick glue in the groves is brittle. Once the glue at the back of the bridge, where the stress is highest, lets go, the joint becomes even weaker, and catastrophic failure is not far behind.

In addition (as if that's not enough) knife scoring the wood of the top introduces 'stress risers'; places where the stress in higher than it 'could' be. Once the joint starts to let go, the wood can simply peel up to the next scribe line, even if the actual glue line doesn't fail. This is not uncommon on cedar tops if the maker gets a little too zealous scoring around the back edge of the bridge to clean up the finish. Glue can't get into that narrow cut, so the wood is already 'broken' there.

As I say, there is not total agreement on this in the woodworking community, and I would expect some push-back. It's mostly a matter of balance; which mechanism you think is more important. There is no doubt that most of the volume of wood, and particularly softwood, is air. Filling in that air space with almost anything will make it stronger, so there is a role for mechanical strength. Most of the research I've seen says that tightly fitting smooth glue joints that have been freshly planed or scraped are significantly stronger than ones that have been sanded smooth, or left to oxidize for more than about 15 minutes. That research goes back to WW II, and was done in the US Dept. of Agriculture Forest Products lab, so it's public domain.

printer2
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Re: Catastrophic failure - any hope of repair

Post by printer2 » Tue Mar 12, 2019 12:00 am

Just spray the latice with Gorilla Glue filling the structure, slap on the bridge and clamp.



Kidding.
Fred

ernandez R
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Re: Catastrophic failure - any hope of repair

Post by ernandez R » Tue Mar 12, 2019 1:12 am

printer2 wrote:
Tue Mar 12, 2019 12:00 am
Just spray the latice with Gorilla Glue filling the structure, slap on the bridge and clamp.



Kidding.
Kidding?

I think you and I would have had this top trauma back to playability in a tenth of the time it took everyone up-thread to wring their purls.

I would have glued the bridge back on, an hour or two of prep, epoxy I suppose... Worth a try regardless but it will take skill. I've been glueing things together for fifty years and this doesn't seem too complicated. Of course it won't sound like it did but the only one who would notice was a someone who played it for two hrs a day for a couple months straight. By now even the owner won't recall 100 % what it sounded like exactly... I was 16 the first time I glued a bridge back on...

Knocking on wood I don't ever have to fix one of my builds ;)

A few days ago I was thinking how one could actually splice in a section on this ttop. I was thinking a purposely multi angled inlay somthing with odd lenthed points and mismatched angles to deflect, or rather distribute vibrational energy so the splice seam was sonicly invisible. Kind of like those agles you see on some stealth aircrft that deflect radar energy... Counting to ten for SF to shoot this down, come on brother give it your best ;)

HR
I hate sanding wood or anything else for that matter I just happen to be good at it...

ernandez R
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Re: Catastrophic failure - any hope of repair

Post by ernandez R » Tue Mar 12, 2019 1:29 am

Stephen Faulk wrote:
Mon Mar 11, 2019 1:59 pm
Just for fun, have someone try gluing the bridge back on with cleats fit between the lattice. Put a light in side the guitar and trace the lattice pattern with the bridge laying on the hole.

Then have them fit patches of thin spruce into the squares of open top under the bridge and glue them in with a caul. Then glue the bridge to the new substrate under the bridge and try to consolidate all that loose wood and splinter under the bridge. It will be a shoemakers job, but you never know it might last another ten years if done well.

The diagonal scoring and scoring around the bridge looks like a major oversight on the part of the makers. Bridges don't need scoring on either the bridge or the top.
Ha, I didn't see you had already suggested a repair scheme. Sounds doable. I was trying to incorporate some .006" solid lamanate uni CF in there to tie it back together, longatudanlly to give some stiffness back to the repair area. Like skinning a cat but more like tossing a cat at midnight in a graveyard. You might end up with worts.

HR
I hate sanding wood or anything else for that matter I just happen to be good at it...

Stephen Faulk
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Re: Catastrophic failure - any hope of repair

Post by Stephen Faulk » Tue Mar 12, 2019 1:52 am

ernandez R wrote:
Tue Mar 12, 2019 1:29 am
Stephen Faulk wrote:
Mon Mar 11, 2019 1:59 pm
Just for fun, have someone try gluing the bridge back on with cleats fit between the lattice. Put a light in side the guitar and trace the lattice pattern with the bridge laying on the hole.

Then have them fit patches of thin spruce into the squares of open top under the bridge and glue them in with a caul. Then glue the bridge to the new substrate under the bridge and try to consolidate all that loose wood and splinter under the bridge. It will be a shoemakers job, but you never know it might last another ten years if done well.

The diagonal scoring and scoring around the bridge looks like a major oversight on the part of the makers. Bridges don't need scoring on either the bridge or the top.
Ha, I didn't see you had already suggested a repair scheme. Sounds doable. I was trying to incorporate some .006" solid lamanate uni CF in there to tie it back together, longatudanlly to give some stiffness back to the repair area. Like skinning a cat but more like tossing a cat at midnight in a graveyard. You might end up with worts.

HR
Really more like the equivalent repair on a steel string guitar. It’s like fitting a very thin light ‘bridge plate’ between X braces. I’m pretty sure it would hold if skillfully executed. But it would stiffen the bridge area a bit, maybe add 5 to 6 grams at most- I would slip in three squares of spruce 1mm thick in between the braces under the bridge. Then clean the bridge and glue a patch cross grain over the thin plate cleats then glue the bridge back on.

I’m pretty sure it would hold, it you analyze the condition the braces are still intact, the problem is the scoring allowed the thin top to break away from the braces. A carefully made cross laminated structure glued to the top and braces would work, the sound would shift a little more bit because the area is stiffer- who knows it could improve it.

If it were in my neighborhood I’d attempt it because otherwise the top is totaled anyway- it’s a possibility in a no win situation.
Patience at the bending iron pays in rounded dividends!

Stephen Faulk
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Re: Catastrophic failure - any hope of repair

Post by Stephen Faulk » Tue Mar 12, 2019 2:07 am

To answer OP’s original question, I’d venture this repair.
DF39DEB8-2DD7-4C7B-BB2D-ECD32752DEAB.jpeg
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printer2
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Re: Catastrophic failure - any hope of repair

Post by printer2 » Tue Mar 12, 2019 10:57 am

Stephen Faulk wrote:
Tue Mar 12, 2019 2:07 am
To answer OP’s original question, I’d venture this repair. DF39DEB8-2DD7-4C7B-BB2D-ECD32752DEAB.jpeg
What I would try, minus the Gorilla Glue.
Fred

Stephen Faulk
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Re: Catastrophic failure - any hope of repair

Post by Stephen Faulk » Tue Mar 12, 2019 11:49 am

printer2 wrote:
Tue Mar 12, 2019 10:57 am
Stephen Faulk wrote:
Tue Mar 12, 2019 2:07 am
To answer OP’s original question, I’d venture this repair. DF39DEB8-2DD7-4C7B-BB2D-ECD32752DEAB.jpeg
What I would try, minus the Gorilla Glue.
I noticed after I wrote that that up thread you described something similar.
Patience at the bending iron pays in rounded dividends!

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Ken Whisler
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Re: Catastrophic failure - any hope of repair

Post by Ken Whisler » Tue Mar 12, 2019 10:27 pm

On a related side note, there was a Hauser II in my locale that Yuris Zeltsin (sp?) replaced the original bridge, which stayed in the case compartment. There was clearly a cross hatch pattern scored in the underside of the original bridge. Long before the days of smartphones and I did not have a camera on hand.
Ken Whisler, guitarist and luthier

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Arash Ahmadi
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Re: Catastrophic failure - any hope of repair

Post by Arash Ahmadi » Tue Mar 12, 2019 10:44 pm

Good thing it didn't happen as you were playing it... it could hurt you too... something must have been wrong with its construction, right?
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Peter_T
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Re: Catastrophic failure - any hope of repair

Post by Peter_T » Wed Mar 13, 2019 5:33 am

I may have missed it, but @dougcalton did you contact the luthier about this? I'm unclear why you'd entertain fixes from anyone else, when the break is quite clearly a build issue.

dougcalton
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Re: Catastrophic failure - any hope of repair

Post by dougcalton » Fri Mar 15, 2019 10:34 am

Luthier was a chinese violin shop. Not considering shipping to China, also the person that commissioned their work had a falling out with them over other business issues and had not been in contact with them for several years. Just didn't make sense to pursue further. Besides, my wife told me to buy a new guitar, so - well, you know.....
1989 Marin Montero
2015 Slavko Mrdalj Lattice Top cedar, double back and sides indian rosewood

Stephen Faulk
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Re: Catastrophic failure - any hope of repair

Post by Stephen Faulk » Sat Mar 16, 2019 7:18 am

So where is the broken guitar?
Patience at the bending iron pays in rounded dividends!

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