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To be on the safe side, I try to leave Titebond and LMI clamped for 30 minutes, then I'm carving. Never had a problem. HHG maybe an hour although, I'm a little unsure of it, and wouldn't be flexing on it for a couple hours.

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Pat

Michael the relevence of grain orrientation is important in so much as the expansion and contraction of the various glued elements will expand and contract at different rates depending on grain orrientation. It's the "real world" of how a guitar is made if you will with a bridge being a perfect example.

Not trying to drag on a debate on the virtues of fish glue (or not....) and I also want to apologize to the OP for the likely unwanted distraction from what they asked about.

However if you want your test to have any value at all to those of us in the insdustry who reglue bridges more often than we care to the test has to address a more realistic view of the real world life of a wooden musical instrument. Again my hat's off to you for doing testing!

I think bridges coming unglued has little to do with the glue used, other than the fact that hide glue breaks apart easier, and fish glue seems to let go in high RH according to reports, I've never used it.

Most bridges are glued on flat or pretty close to the top dome. Over time the top distorts, but the relatively thick and stiff bridge has a hard time conformng to the new geometry and resists contorting, which is part of how it does it's job. Eventually the stress becomes too great and the shape of the top forces the bridge to separate at a weak spot, usually behind the bridge where the distortion is roundest.

In that case, a relatively weak glue like Hide can simply fail and pop the bridge off, not necesarily a bad thing, considering that a stronger glue like Titebond can pull bridge fibers off along with it, or cause other damage, or partially separate and be tough (for some people) to remove. For that reason I consider hide the best glue for bridges, because they will eventually need to come off and be reshaped anyway.

BTW hide glue is not really "Crystaline" as it has been described. It's an organic polymer called Collagen, not a crystal. It cracks apart easily and can be ground into powder because of the weak bond between the monomers. Scientifically, animals glues are thermoplastics just like titebond but weaker and therefore exhibits different properties, but it's also subject to thermoplastic creep as a result of being thermoplastic.

Here's more information on Collagen: http://en.wikipedia.org/wiki/Collagen

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Old growth, shmold growth!

Bridges pop off for all sorts of reasons. I've seen plenty of bridges glued with HHG that show a lot of wood fibres. I'm also pretty certain that sizing a joint gives a stronger bond as far as HHG is concerned. So a re-glued bridge may well give a stronger joint.
Fish glue may need a slightly different technique. I have a slight suspicion that it gives a thicker glue line than HHG if it isn't handled in a different way. That suspicion comes from planing off a fretboard that had been glued with Fish glue. The film seemed to be much thicker than the equivalent HHG joints. I've also noticed it with a Spruce centre joint that I've done. Perhaps applying the glue, allowing it to sink in and then rubbing the joint to remove excess (clamp after) might give better results. Of course that's a lot of supposition on my part. I use Fish glue for gluing in frets and laminated Backs, so I have little experience of it on other joints of the Guitar. The rest is all HHG, of which I have over 20 years experience.

I'm of the school that says it's not so much about the glue as about how you use it. But putting that aside for the moment, Chuck raises some interesting points.

Having never seen a published comparative creep test between Titebond and HHG, would you be of the view that HHG joints are not observed to creep because they fail prior at a lower stress than Titebond will withstand?

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Just out of curiosity, what are we taking as evidence of "creep"?

Having worked on several thousand acoustics from many different eras, I'm not convinced I've seen significant differences in aging patterns between hide glue guitars and modern glue guitars.

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Old growth, shmold growth!

One form I've seen is bare wood behind the bridge and rucked up finish in front of the bridge. It's possible that this example suffered heat stress, too. Also likely that this was a "cheap and nasty" white PVA glue rather than one of the better quality ones.
I don't do much by way of repair work, but I do see a lot of guitars and I'm inclined to agree.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Put me down as another in the 30 minute camp. I have done some of the testing and found that if you hit to shear 2 pieces that were clamped for 30 minutes right out of the clamps, it is pretty easy to get them apart. But the same piece clamped for 30 minutes tested after 24 hours - same as clamping for 24 hours. So just donut stress it too much in the early stages.

I heard someone on another forum say they glued a bridge with TB and strung it up after 6 hours with no problem.

I don't think that I would agree that Titebond makes a superior bond to HHG.

HHG is less forgiving with the joinery that's for sure but both HHG and Titebond are capable of being stronger than the wood in break tests. What more is there than that in respect to bond strength... irrespective of sheer, etc.

I've never observed any creep with HHG but we have seen it a number of times with Titebond. I have had one of my own guitars when it reached 7 years old have the Titebond glued bridge creep forward plowing finish and exposing the glue line on the back edge of the bridge. This early guitar for me has lived in a climate controlled environment the entire time - my man cave.

Regarding top distortion and bridges many of the bridges that we remove on older Martins and Gibsons are very distorted and have conformed as best that they can to the top distortion until, of course, deciding to lift.

On 1920 and older Martins with smaller bodies the bridges are often very small and thin and these often, most of the time, show great deformation so much so that they may not be usable and a replacement may be made. On a highly distorted bridge once you get it back to flat there may not be much left and of course there is also the neck angle issue too.

I agree with Trev about how one uses glue being likely as important as the choice of glue. Now if we could just get f*ctories to clean up more finish under bridges which in some cases can expand the wood-to-wood contact area by as much as 40%.... folks would likely have better built guitars as well with fewer bridge failures.

For Chuck I was interested in why you think that HHG is relatively weak? That's not my experience. I have to add to be clear that we are speaking of the same thing and you do not mean that awful Franklin bottled hide glue rasta imposta do you?

For Michael earlier you said that for what you call HHG you use a combination of what we call Pearl glue and what we call HHG. Pearl glue is made from other animal parts and is not the same thing as HHG. It also smells terrible... Not being critical but I am trying to harmonize our collective terminology here so that we can have an intelligent conversation and be sure that we are speaking of the very same things.

Ain't it great to have a good ole glue discussion...

I've actually seen this A LOT.

The reason that I'm inclined to agree with you on the notion that the instruments are suffering heat damage is because I see it most often on brand new guitars straight out of the factory, being unwrapped and inspected in the back of the shop.

The guitars weren't old, and I'm sure they weren't like that AT the factory. The finish being rucked up is another clue. The guitars must have sat for a pretty decent amount of time in a hot truck somewhere.

It doesn't help that most of them were Gibsons either. (Oops, can I say that?) They may have simply been doomed from the start by circumstance of factory.

Then there's Hesh's guitar, a whole other set of circumstances, to which only he can truly comment.

When discussing creep, this seems to me to be the most common situation that people describe to confirm the existence of the phenomenon.

Any other examples?

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Old growth, shmold growth!

Chuck the next time we get one in that has plowed finish in front of the bridge and exposed the glue line behind the bridge I'll take some photos and post them here.

Also you are IIRC correctly down south correct? A hotter climate although these days all bets on that one are perhaps a bit off...

I remember a couple of summers ago when it was stinkin hot here in Michigan how in the morning b*tch sessions that we used to have when the music store was still there and before opening noticing lifted bridges on instruments, new ones.... hanging on the walls. So heat can have a negative impact that's for sure...

I know this thread was originally about brace clamping, but since we've been talking a lot about glue, I have another question. I went to LMI's website to read about their granular hide glue and saw this:

"Hide glue is transparent and can be used as a pore filler by mixing with pigments or sawdust (as do many of the Granada makers); and it sands easily."

Have any of you HHG fans used it for pore filling? I have seen a lot of people pore filling with pastes, and can't help but wonder about the dampening effects of something like that vs something like HHG that is supposed to transfer vibration better than other adhesives.

I know the paste pore fillers are mostly sanded away, but some of it has to be in there.


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You can use it but it's both messy and it shrinks a lot. Tried it.
Hesh. My glue is a mixture of high clarity Hide and Pearl (bone) glue. Nope, it doesn't smell like the cheap dark bone glue that was sold for many years.

Justin what Michael said about using HHG for pore filling, it can work fine but IMHO there are better alternatives. Keep in mind too that often when we review say a historic and/or iconic instrument where HHG was used for seemingly everything the rational behind this was not necessarily best practices/materials but more over what they had available to them at that time. When you see copious amounts of HHG slathered inside guitars with Gibsons being a good example I doubt that there was a lot of thought given to vibrational transfer, very hard glue lines etc. but more likely "hey use this stuff, it works and it's all we have...." Seriously...

I also suspect, highly, that had they had Titebone original that may have been the glue of choice just as similar glues have become the glue of choice these days for many f*ctories.

Michael, bone glue, that's what I was looking for. Anyway that's my point, your HHG and my HHG are not exactly the same thing and that can devalue a discussion a great deal in so much as we are not speaking of the same things here when considering HHG.

Anyway back to fish. Fish is a collagen glue too and although I have not tested it I suspect that it has a very thin glue layer much like HHG. That was part of the great promise for me personally of fish when I first started using it, HHG like characteristics without the short open time. I'm not against fish usage mind you and have a bottle in front of me at the moment in my home shop. I am simply indicating that in our experience, which is considerable and over time with many instruments not just our own builds living the lives for better or worse of how instruments are treated we have had a good number of fish failures all on bridges, all on steel strings, and all occurring 1 - 6 years out after cyclical changes in climate and season. We are not in a high RH climate or an excessively hot one either (I may eat these words this summer...).

David Collins has brought this up before on forums sharing our negative experience with others. On the OLF alone there have been reports of the very same thing from various builders.

I could go on and on here including the fact that steel strings have roughly twice the tension of classicals and I could even make an argument that generally speaking classicals are less likely to be abused since the target market tends to be more mature individuals who may not get off on heavy metal vomit music... etc.

If fish works for you and what you build great! Fish does not work for us in a busy, high-volume three Luthier repair shop in a midwestern US climate where we stand behind our work at times years later as well. When I use a glue that fails it's a huge "shame on me", it costs the business greatly, inconveniences the client and requires that we have their instrument once again to repair it properly, and generally everyone loses. This is NOT the experience that I want for my very valued clients and I don't have to have it repeated over and over to cause me to move swiftly to eliminate the issue. Our solution was no fish for bridges and since we switched back to HHG no failures with likely hundreds of bridge reglues.

Well that's part of the reason for the test. The 'rumour' was that it gave way at relatively low humidity conditions, hence the test at 75% and 85% RH. IF the glue does not show signs of softening at those humidity levels then I suspect it will be fine under the conditions in which I am testing it. The next test will be to increase the temperature and see how the glue reacts to those particular conditions. You can tell a great deal by the glue squeeze out. If it remains glass hard there's more than a fair chance it will be the same in the joint. But there is no doubt in my mind that the Guitars that Alex linked to did not fail because of weak glue or because of stress due to opposite wood grain direction. They failed because the Glue reconstituted at some point. That can only explain the glue 'strings' that he mentions. In fact they can be seen in the photo that shows the fretboard.
From this it is quite evident that Fish glue becomes soft at a certain RH level, that RH level seems to be below the RH level that HHG reconstitutes.

Nothing like a good old glue fight on the internet...

Back to the original question

I use hot hide glue (the Milligan & Higgins 192 gram strength, high clarity 'odorless' variety) for braces. I haven't tested to see exactly how short clamping time you can get away with, but I'm pretty that you could unclamp and start carving after a few minutes, in a pinch. If you have tried to take two pieces that were glued with this glue apart after about 15-20 minutes, you know that it sticks pretty darn well by then. I usually leave braces clamped a couple of hours at a minimum though, I'm normally not in that much of a rush. I use a go bar deck, and my procedure for gluing braces involves two operations for each plate. Back: First, center seam reinforcement, next all braces. Top: Large braces first (X-braces, tone bars, sound hole reinforcement, upper transverse brace). Next, smaller braces, bridge plate, X brace reinforcement. I guess you could cram everything on in one go, but it would be quite crowded, and not necessarily all that practical.

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Rian Gitar og Mandolin

I should amend my post. Gluing braces with TB, LMI, or HHG, I do start carving after 20 minutes clamp time sometimes, but I wouldn't do any vigorous flexing for a couple hours.

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Pat

Well for one thing, you can crack a violin apart pretty quickly and easily with just a palette knife slipped around the perimeter, no heating. Try that with Titebond.

Also it seems to me in literature that I've read that HHG routinely comes in last in various "Glue Shootouts!" that I've seen in magazines over the years.

That being said, we know that it can be used in instrument building without a doubt. I'm just saying that some of the properties we are observing are likely due to the weaker bonds between monomers VS some kind of mythical "CRYSTALINE" molecular arrangement. HHG is an organic thermoplastic polymer.

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Old growth, shmold growth!

Violins are intended to be broken open easily. They deliberately put on a very watery weak glue. Just as well too, they aren't fools.
Those magazines should let me do their HHG joints. They just might get a different result!

Maybe, but those guys doing the tests I'm pretty sure know what they're doing.

They are typically performed in facilities that specialize in that sort of thing and research the optimal application technique according to the manufacturers.

It's not controversial though, or at least it shouldn't be. HHG glue is PLENTY strong for all guitar and other stringed instrument related applications without question.

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Old growth, shmold growth!

A lot is made of the extra tension steel strings have over nylon strings.

But consider that for a TRADITIONALLY made steel string, Most or all of the tension is taken up by the truss rod, neck joint, and internal bracing, I would say most of it is on the neck.

The strings are anchored to the tuning machines on one end and pinned through the bridge and anchored against the bridge patch internally on the other end. The glue joint for the bridge desn't really have to resist direct string pull, and instead is stressed mainly by resisting the top torsioning and trying to deform. Most of THAT stress is taken up by the internal braces, although over time the top distortions can become quite great. theres also some leveraging of the strings pressing forward on the saddle, so there's so shear and rotational stresses. The ball ends of the string being anchored internally though transfers most of the worst string tension stress directly to the top of the guitar.

Contrast that with the classical bridge which has the strings tied on to the actually bridge itself so that all of the tension is pulling directly on the bridge glue joint.

There's also the alternate string-through steel string bridge in the same situation, but I myself have seen enough broken bridges where the wood has failed to stay away from that style of bridge myself. It should be noted that even in those situations it was the WOOD that failed, not the glue, although most of the ones I've seen have been glued with modern synthetic polymers. When those start to let go, they can fail pretty quickly and take the top out with it.

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Old growth, shmold growth!

They may well know what they are doing but if I wanted the strongest HHG joint I would certainly size the wood first. It's something I came to realise over many years of using Hide glue. The strongest joints seem to be when they have been reglued.
Probably the instrument to look at when considering how strong HHG is at gluing bridges is the Vihuela. Low tension instrument at around 35 Kg total string pull (circa 40 Kg for a Classical), but not only are the strings tied directly to the bridge but that very bridge has an extremely small footprint. It's gluing surface is probably less than one fifth of that of a modern Classical Guitar bridge. So it's only 5 Kg less than a Classical but a mere fraction of the gluing surface.
Do they pop off? Occasionally but they can go decades without doing so.

Good thread, guess I'll cut down my clamping time a little on braces. Thanks.

I do notice that when I glue bridges with hide and clamp overnight that when drilling out the pin holes the column of built up glue can still be a little rubbery and clog the bit. If I wait another 6-8 hrs after unclamping it has become hard. I cover the pin holes with clear packing tape under the caul if that means anything.

I'm still going to clamp bridges overnight and wait another day before stringing up.

Hey Hesh,
If you guys are regluing say a Martin bridge that was originally glued with Tightbond do you use hide for the reglue?

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

Hide glue is thermoplastic, it likely became rubbery on the drill bit as the bit was likely hot from friction.

I notice the same thing with Titebond and other polymers.

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Old growth, shmold growth!

That's a good thought but actually the glue was rubbery before I drilled it, I could tease it out with a dental probe.
I'm pretty generous with hide on bridges so it wells up in the holes a bit. I thought the tape covering the pin holes and lack of air might have done it as it hardened up within 6-8hrs after the clamps were off. Once hard it drilled fine.

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