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Weird. Any speculation as to what went wrong? Just a sour batch of glue?

Along with the hole for the UST, I see two other holes that look to have been filled with glue or some other white substance. I would guess for alignment pins during glue up
But I would expect them to be u dee the saddle. What is going on there?

Any guess as to what caused this? It is hard to tell from the picture on my little phone screen. It looks like mostly glue on the bridge with some wood failure but mostly glue failure. Is that right? I would suspect thick glue line from bad mating surfaces or substandard clamping but the nicely selected top makes me guess the maker would have bridge glueing down pretty well. I don't suppose the owner fessed up to any poor treatment that might provide a clue.

Edit: just zoomed in more on the pic. A lot more wood than I thought. I'm guessing sharp impact to the back of the bridge. I'll be following this thread closely; my curiosity is piqued.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I have seen several bridges like that, Todd. Sometimes a reason for failure just can't be ascertained. Just clean it up, reglue, and send it back is all you can do.

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"Act your age, not your shoe size" - Prince

So did the locating pin just shear off? It sounds like it could have been a warranty repair.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Chris, I'm sure you are right but as a guy who is still learning, it sure would be nice to know how these things happen. None of the (small number of) bridges I have glued have come loose but I can't help but worry when it happens to experienced makers. I'd sure like to learn from other's mistakes, I don't have time to make them all myself.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Nice pic. So, is this mainly a wood failure rather than a glue failure?

Bryan, I'd guess the pin holes were used for locating the bridge during CNCing, then reused with short plastic pins for locating to the top. I think that's how Taylor does it.

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David Malicky

Huh, that is a stumper. Maybe a really good, near-zero runout top, but someone scored around the bridge with a razor before scraping/routing the finish off, and the score line cut through the top layer of wood fibers? That's more of an issue with cedar and redwood since their splitting strength is so low, but I suppose it could happen on spruce as well.

Totally unexpected!!! Wood failing, glue holding? How much force would it take to do that?

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Joe Beaver
Maker of Sawdust

I think it could be a problem with medullary rays. That top has a lot of them. The medium strings don't help. I agree that scoring the finish might also be a problem.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

could this be an effect of sanding the bridge footprint too finely at glue up? not enough "tooth"?

Glue does not need an anchor. The best glue joints are done with a jointer which leaves a surface that is very smooth. It could have simply been a bit of dust on the surface when it was glued up.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

But then the bridge would have peeled off without tearing any wood.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Todd,
What are the weird stains on the top, by bridge and on rosette ? Looks like water damage to me.

Could be the residue from the heat used to release the bridge?

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Todd:
Too deep when cutting outline of bridge, especially at the back. Once peeling starts, it's game over. That's my best guess. Looks like the glue did a super job of holding the bridge. But..................
Tom

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A person who has never made a mistake has never made anything!!!

I never considered that.. but the soundboard would have to have such perfect runout in order to do that...

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

It seems like some varieties of spruce absorb more glue than others. I had a couple of early Lutz failures when I was in kind of a stingy glue era. I didn't want to have gobs of squeeze out to deal with.
The Lutz definitely soaked more up.

The technique by Collings looks impeccable. It does look like there is a ledge routed in the bridge. Road guitar, lots of top movement from temp and humidity changes, just bad luck I guess. Sounds like it's fixed right now. Interesting post Todd, thanks.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Medullary rays run perpendicular to the other fibers and introduce some narrow strands of runnout between the other fibers. They usually don't pose a problem and are a sign of a nice well-quartered top. In this case there might be enough of the rays to line up and affect the structural integrity of the other fibers especially in a top that has no runnout in the long fibers.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

That's what I was thinking. Perhaps the wood "split" on a plane that is coplanar with the rays.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

When I look at the photo, I see spruce pulled up in some areas but only see glue on the bridge in others. Looks about 50/50 to me from here. That is what you would expect from typical shop dust contamination. It would not be like there was a coating of dust over the entire surface. That would've been noticed and brushed away. It would have been a bit of dust here and there, perhaps from dusty fingerprints.....or a dozen other ways. Shops are dusty and if enough of your joint is contaminated it will fail. Especially in a high stress situation like this.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

...i still can't figure out why wooden dowels/pins aren't commonly used to hold down acoustic guitar bridges

Wow, I just now got a chance to look at this picture on a bigger screen. I couldn't tell that it was almost all wood. It looked like half glue and half wood before. I don't suppose there is much the maker could have done wrong here. The wood just failed.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

That is a serious eyebrow archer. Could the bridge have been dinged with the force parallel to the top somehow?

I think it could be related to the rabbet cut into the edge of the bridge to allow it to overlap the top. I know a lot of folks do this successfully, but I have always been afraid that the stress riser at the back of the bridge could allow the edge of bridge joint to pull free. And if it starts, this delamination would continue across the joint in a situation like this with somewhat perfectly parallel grain on the top. Just a theory.

Actual spruce fibers? or spruce dust stuck at the bottom of the glue?.....I blow the photo up until the resolution pixelates and I cant tell from here. But I do know that dust contamination will cause failures in other applications that look very similar. Another thing I see is that I can follow the tool path quite clearly, especially on the spruce. Every little edge left by the tooling is just like a little cut in the surface of the spruce. That is the main reason I only routed the finish off of two or three guitars and went back to scraping. Those tool path marks concerned me on my own work even though I know major manufacturers get by with it quite well. But if you look closely at those tool paths in the spruce It appears that there are fairly good sections that show no fuzz as one would expect when the wood fibers pulled up, especially to the wing side of the bass E peg hole. I'm staying with contamination of the joint, most likely dust, based on what I can see without a hands on inspection.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/