Testing hot hide glue strength - FRETS.NET2024-03-28T20:17:34Zhttps://fretsnet.ning.com/forum/topics/testing-hot-hide-glue-strength?commentId=2177249%3AComment%3A138619&x=1&feed=yes&xn_auth=noForgive me please in so much…tag:fretsnet.ning.com,2014-10-18:2177249:Comment:1386192014-10-18T15:37:15.476ZHesh Breakstonehttps://fretsnet.ning.com/profile/HeshBreakstone
<p>Forgive me please in so much as I have not read every reply in this thread so I may be redundant at times....</p>
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<p>First the overall impression that I received reading the first page of this thread was that some folks, not all... are making this WAY more complicated than it needs to be...</p>
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<p>Picture this: A factory back 40 years ago in Kalamazoo, Michigan where the workers, Gibson folks, had hot pots running all day (and likely all night too forgetting to pull…</p>
<p>Forgive me please in so much as I have not read every reply in this thread so I may be redundant at times....</p>
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<p>First the overall impression that I received reading the first page of this thread was that some folks, not all... are making this WAY more complicated than it needs to be...</p>
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<p>Picture this: A factory back 40 years ago in Kalamazoo, Michigan where the workers, Gibson folks, had hot pots running all day (and likely all night too forgetting to pull plugs...) with a mass of HHG in them, a couple of brushes, and the "limited" knowledge that it actually takes to use HHG properly.</p>
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<p>They would prepare a joint (and not always well either...) and "slather" it on say the bottom of a brace, position and clamp endeavoring to do so quickly.</p>
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<p>The primary concern when using HHG and I am speaking of the real deal stuff say from M&H and never that awful Franklin bottled rasta imposta stuff is the very short open time.</p>
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<p>As such one needs to have things set in place, parts, clamps, etc. in approximately 15 seconds or less. Any more time and with out using one of the methods to extend "open" time one risks a compromised joint.</p>
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<p>With this in mind consideration needs to be given to where to use HHG as well as how to use it and again none of this is difficult to understand once you work with the stuff every single day and have success in doing so. A great example of where to use HHG in my opinion is any joint that needs to perhaps be "serviceable" in time such as gluing on a bridge. Personally I'm hip to the very thin, microscopic glue line resulting AND the very hard, crystalline nature of dried HHG believing as I do, for now... that it's sonically superior in applications that have sonic impact.</p>
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<p>With bridge gluing we also have to observe the shortcomings of HHG meaning that our bridges need to be excellent fits with no unnatural acts required with the clamping, positioned in place quickly and the clamps snugged up before the stuff starts to jell.</p>
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<p>Dry runs are your friend with HHG or any glue for that matter....</p>
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<p>For me it makes perfect sense believing in the qualities I've mentioned so far to use HHG for all braces, bridge plates, bridges, etc. where we want the tone woods to interact well with as little dampening as possible.</p>
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<p>The violin maker was "sizing the joint" as per the OP's post which although I see no harm in it is not at all necessary with HHG AND not how the vast majority of HHG users (dead or alive) use or used it.</p>
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<p>Again the beauty is that if your chops are down, your parts fit, your methods sound, your experience positive, and you are mindful of working time you simply slather it on, clamp and Bob's your uncle. Man that Bob guy gets around...</p>
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<p>Regarding viscosity I disagree with one comment that I read here that indicated that it does not matter. Typically viscosity does not matter all that much unless one is seeking a creative way to extend open time for an application that requires more open time no matter how good your chops are. For example gluing on a back plate on a new build in a go-bar deck. For me I am positioning 30 plus go-bars (and trying hard to not get hit in the face if one slips...) as well as some clamping cauls to protect the plate from the go-bars. Although it's arguable if HHG has an advantage in this application we HHG snobs nonetheless endeavor to use HHG in this application for the same reasons that man (or woman) climbs that mountain. And no it's not because we are stupid... although that can be true... it's because HHG is what we may have handy and ready, something we are comfortable with, it's tradition in guitar building, and some believe that for gluing on a back plate it' sonically superior. </p>
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<p>For this application a higher gram strength has the added draw back of jelling even quicker so why would one use a higher gram strength for gluing on a back plate in a go-bar deck? Because according to Mario P. aka Grumpy and tested and confirmed by me as well you can lay down a thick bead on the rim that remains a bead and does not flatten out as quickly as regular strength HHG. The bead becomes self insulating to a degree with the most exposed walls of the bead starting to jell but also protecting the runny liquid HHG inside the bead from jelling. Position the plate, the go bars, etc. and you just extended the open time and applications for HHG. Some preheating of the rim is advisable too. When the clamps are positioned that bead is smashed and the runny, still hot HHG spreads out. This is a rather brilliant trick that many of us learned from Mario/Grumpy.</p>
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<p>For bridges we have a method that can have all of the clamps in place in under 15 seconds. But if I am feeling pokey, and I often am..., I might pop the bridge in a microwave for 15 seconds so that the warm bridge will also extend the open time of the HHG.</p>
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<p>HHG is easy to use, easy to understand but it does have limitations and if you don't pay attention to things such as open time it will bite you.</p>
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<p>Regarding joints - recently I read on another forum a post by a member who insisted that HHG had great gap filling capabilities. WRONG..... Buzzzz..... resubmit in 30 days and try again....</p>
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<p>HHG sucks at gap filling and IMO is not even as good as Titebond original which is a fine glue by the way too but also not billed as a gap filler!</p>
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<p>HHG joints require superior joinery and attention should be paid to one's joints if using HHG. Again that microscopically thin, molecular level bond also comes with the price tag that it is no substitute for poor joinery and workmanship.</p>
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<p>Regarding a sanded joint vs a freshly scraped joint the thinking is that sanding creates dust and contamination that interferes, at the microscopic level with a complete wood-to-wood bond. As such it's believed that a freshly scraped joint has more "joint energy" for lack of a better descriptive term.</p>
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<p>So again picture that nasty old glue pot that has not been cleaned in ages because no one wants to do it, a couple of brushes sticking out of the pot, craftsman and women slathering it on to well fitted braces, clamping and moving on. And never, never, never forget the idea and need for serviceability so that your creations can be easily serviced in the future should Mr. or Mrs. Customer screw up and sit on the thing.... because they will and do.... often....</p>
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<p>By the way there are examples of Egyptian furniture assembled with HHG that are 2,000 years old that are still doing fine. It's great stuff and part of the greatness is the ease of use within the stated limitations of course.</p>
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<p>Lastly wouldn't it be great if there was a glue that for applications such as a loose brace in say a mando where we can't get an arm in there to clean out the failed glue that some new glue and the ability to reflow the old glue would get the job done? This is yet another attribute of HHG, it can be reflowed in time. Great stuff.</p> Rusty,
Appreciate your though…tag:fretsnet.ning.com,2014-10-18:2177249:Comment:1385382014-10-18T12:05:16.738Zjbbancrofthttps://fretsnet.ning.com/profile/JamesBBancroft
<p>Rusty,</p>
<p>Appreciate your thoughts. But, how to use HHG is not a big secret nor do you need a whole lot of training.</p>
<p>Of course violins and guitars are different, but they are both made out of wood and held together with glue. As far as mixing HHG, applying, and clamping, they are the same for whatever instrument they are use on. Besides you strive for the most solid joint no matter what the instrument, that's my plan anyway.</p>
<p>This idea of using different glue/water ratios…</p>
<p>Rusty,</p>
<p>Appreciate your thoughts. But, how to use HHG is not a big secret nor do you need a whole lot of training.</p>
<p>Of course violins and guitars are different, but they are both made out of wood and held together with glue. As far as mixing HHG, applying, and clamping, they are the same for whatever instrument they are use on. Besides you strive for the most solid joint no matter what the instrument, that's my plan anyway.</p>
<p>This idea of using different glue/water ratios for different applications I've found not to be true. I use the same glue/water mixes for all joints. That is why I mix it, "water thin".</p>
<p>Now if your going to do surgery on the human body, you need extensive training. Some things are much simpler to learn and do right, and using glue is one of them.</p>
<p>My occupation was a Wild land Fire fighter for the state DNR, Forest Management Div. All my fire training was on the job, and I had no college degree. When the state needed more people to do timber inventory, I had OJT for that too, and did that job satisfactory, where generally you needed a forestry degree.</p>
<p>So, it boils down to the fact there are many things you can learn and do without extensive training or a college degree.</p>
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<p>Jim </p> Hi Jim,
It's axiomatic that…tag:fretsnet.ning.com,2014-10-18:2177249:Comment:1384572014-10-18T06:06:07.065ZRussell Vancehttps://fretsnet.ning.com/profile/RussellVance
<p>Hi Jim, </p>
<p>It's axiomatic that doing stuff right from the beginning and understanding why you do what you do is important to both tradesmen and artisans alike. If everyone could use glue successfully we wouldn't be using time pointing out the correct way to go about it and the things that affect it. Nor would Frank have to do tutorials on it's use. </p>
<p>You are obviously entitled to have your opinion about those who strive for perfection or who have a tertiary qualification or a…</p>
<p>Hi Jim, </p>
<p>It's axiomatic that doing stuff right from the beginning and understanding why you do what you do is important to both tradesmen and artisans alike. If everyone could use glue successfully we wouldn't be using time pointing out the correct way to go about it and the things that affect it. Nor would Frank have to do tutorials on it's use. </p>
<p>You are obviously entitled to have your opinion about those who strive for perfection or who have a tertiary qualification or a background in science or engineering or luthiery but I don't see that as being any "big deal" - it's simply a way to establish ones credentials in the various areas we discuss here. </p>
<p>Similarly, Violins are to guitars as apples are to oranges - over-engineered, short scale, low tension joints in violins are not under the same stress as modern long scale 6, 7 and 8 string instruments with steel stings and skinny neck sections etc. Hot hide glue is all violin makers and repairers use because it is traditional and all they need to use. Not to say they are Luddites, they simply don't need high performance adhesives or practices in their repertoire.</p>
<p>HHG is alway good for a host of posts.</p>
<p>Rusty.</p>
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<p> </p> You want to know and learn a…tag:fretsnet.ning.com,2014-10-18:2177249:Comment:1383782014-10-18T01:47:27.685Zjbbancrofthttps://fretsnet.ning.com/profile/JamesBBancroft
<p>You want to know and learn a few things about hot hide glue, talk to some good violin repair people. Hot hide glue is all they use.</p>
<p>The truth be known it's not that difficult to learn to use successfully. I've always mixed it water thin no matter what the application, too thick is a major problem in my opinion, it just needs to be slippery between your fingers. Warm the parts to be glued and you will have good success with it.</p>
<p>I've never experimented with gluing a joint and…</p>
<p>You want to know and learn a few things about hot hide glue, talk to some good violin repair people. Hot hide glue is all they use.</p>
<p>The truth be known it's not that difficult to learn to use successfully. I've always mixed it water thin no matter what the application, too thick is a major problem in my opinion, it just needs to be slippery between your fingers. Warm the parts to be glued and you will have good success with it.</p>
<p>I've never experimented with gluing a joint and trying to break it once cured, but I have glued just about any joint you can think of, and had very few failures in over 40 years of using this glue.</p>
<p>After reading a few other replies, it seem people make a big deal out of the glue/water ratio and having everything just perfect and having a masters degree in it's use. Anyone can use this glue successfully.</p>
<p>If I was to stress one point, it would be to mix the glue water thin, too thick you will always have problems.</p>
<p>The consistency of thin maple syrup is best, or slippery between your fingers.</p>
<p>Jim</p>
<p></p> When I first tried to use HHG…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1385002014-10-14T22:56:36.563ZNed Knepphttps://fretsnet.ning.com/profile/NedKnepp
<p>When I first tried to use HHG, I didn't know anyone that used it and didn't have access to any advice on the subject. What I had was a can of granulated glue bits that smelled funny. The can it came in included instruction for preparing it for use. (Note that I placed a "full stop" at the end of that sentence.There was nothing about how to actually use it.) Following the instructions, I made it up a batch and the results were OK when I used it for the first time. After that it didn't work…</p>
<p>When I first tried to use HHG, I didn't know anyone that used it and didn't have access to any advice on the subject. What I had was a can of granulated glue bits that smelled funny. The can it came in included instruction for preparing it for use. (Note that I placed a "full stop" at the end of that sentence.There was nothing about how to actually use it.) Following the instructions, I made it up a batch and the results were OK when I used it for the first time. After that it didn't work so well anymore. ( BTW, it's not particularly funny or cool when the chair you fixed falls apart with your mother on it.,, even if you think it is. Just take my word for it.)</p>
<p>It took a while but I started figuring out how to work with it. Although I did learned how to cook it and work with it the whole thing was pretty frustrating and not nearly as linear as I'm making it sound here. The result is that I think I have a better understanding of how to use it than I would have otherwise.</p>
<p>I'm not saying to ignore all the information available now. I'm saying that experiences vary just like the working environment varies from person to person. The information that's out there can save you a lot of time and trouble but what's important is to learn how it works when YOU use it. Experimenting with blocks isn't a bad place to start if you're concerned about basic handling but it's probably not going to tell you all that much about how things work when the glue surfaces are not straight and flat or how to get a clamp into place on a curved/rounded part. My personal opinions is that you will learn more quickly if you got a junker guitar from somewhere to take apart and put it back together using HHG. Doesn't matter if it holds up or not if you learn how to use the glue in the process. You may even be able to get more experience if you want to return to what failed to hold up and repair it again once you get the hang of using HHG. The point is for you to learn how to work with the glue. </p>
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<p>One of the opinions that I've developed is that HHG is actually somewhat more forgiving then most of the information we read indicates. If I want the joint to be as strong as possible, I do think that follow the rules closely will insure that. Heat the glue surfaces and have the clamp up material ready and waiting. ....the results will be a very strong joint.</p>
<p>But my reality is that I'm cooking my glue in a pot in my garage. The RH is something I check on the weather channel and my technique for controlling it boils down to a "work today or not " decision. There are a lot more issue in my work than if I'm optimizing the glue joint in every instance. I would probably be better off using something more modern but most of the instruments I work on were made with HHG and I have just enough ego to think that some of my work will last long enough that some future hobbyist might want keep it going. If that happens, I'd really like to have them think kindly of me so I try to avoid introducing too many "gotcha's" in what I deliver to them, thus HHG . Besides, I actually like working with it now.</p>
<p>I suppose I'm saying is that we should probably consider that every glue has an a set of optimum working parameters. Holding to those as closely as possible is desirable IF you have the wherewithal to do so to. Fortunately for me, most glues we use today will actually work at a high percentage of their max performance even if I miss their strike zone by a bit. Some of what I glue with HHG is not as critical or as stressed as other parts. I'm really not nearly as concerned about the splints/braces that I add to the sides of the old guitars I restore as I am the bridge or neck joint. Most of these instruments didn't have any support/crack control to begin with and the addition I make is just a bit of insurance for an old dry guitar side. I'm not likely to heat the parts before gluing and I may not have a clamp waiting in the "almost" position. If I take slightly longer to get a clamp in place and the glue is starting to gel just a bit when I get it on, I'm not going to loose sleep. It's not the strongest bond but it's enough for the job. Some glue joints are just more important then others The line may not be wide but there;s a bit more room for error on that joints that aren't so critical/stressed. That little bit of room can make it a lot easier to work with the glue in some instances.</p>
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<p>It is important to learn how to use HHG. It's an archaic form of glue by today's standards and it's not as forgiving as modern glue but I honestly don't believe it's as unforgiving as we often think. It's been in use for a very long time and I don't believe that all of those joints and veneers were done with perfectly prepared glue used under ideal conditions. The glue is still around and in fairly common use today because it works well AND because it's not impossibly hard to use. You just need to learn it's "particulars" and using it on something "real world" will teach you faster than anything else. </p>
<p>( Please Note; No animals were harmed within sight of the poster, during the production of this post. The poster is in no way responsible for what may have happened beyond the confines of his "sight". All opinions are subject to review even if there is not possibility of change. Any resemblance to or reference of real people, living of dead, is possibly coincidental and, probably inadvertent, with the exception of the poster's reference to his Mother. In that particular instance, She was very real and VERY "advertent".) </p> Just some thoughts.
Hide glu…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1383372014-10-14T15:49:52.961ZDavid Farmerhttps://fretsnet.ning.com/profile/DavidFarmer
<p>Just some thoughts.</p>
<p>Hide glue in dry form is very stable. As long as it's been kept dry and relatively cool, it's likely just as it was when it was made. Probably more so than Titebond. If it's not clumped together, it is almost certainly fine.</p>
<p>I think the ,"testing" you need, is for your methods of using it. Experiments that will give you experience and a feel for how to work with it as quickly as possible. To that end, I would try some scrap tests of the extremes of…</p>
<p>Just some thoughts.</p>
<p>Hide glue in dry form is very stable. As long as it's been kept dry and relatively cool, it's likely just as it was when it was made. Probably more so than Titebond. If it's not clumped together, it is almost certainly fine.</p>
<p>I think the ,"testing" you need, is for your methods of using it. Experiments that will give you experience and a feel for how to work with it as quickly as possible. To that end, I would try some scrap tests of the extremes of use.</p>
<p>Make a bunch of pieces. Glue some together with the glue deliberately too thin, too thick, too hot, to cold, clamped together quickly, after 30 seconds, a minute, two, three, surfaces very rough, Just planed, etc.</p>
<p>These tests will give you more of what I think you need for confidence. Not confidence in Hide glue's strength, but in your ability to use it well. Doing things wrong deliberately, is often more illuminating.</p>
<p>One last thing. Don't be seduced by a thermometers digital display or lots of decimal places on it. If it is a cheep one, get another, or two, and see if they agree. Boiling water is 212 degrees at sea level, about -2 degrees for every 1000' of elevation above that. It's a quick test to make sure a thermometer is not way out of whack.</p> Thanks David, that's a really…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1380772014-10-14T14:57:12.324Zeliyahttps://fretsnet.ning.com/profile/eliya
<p>Thanks David, that's a really informative reply. However, this isn't what I'm asking. I'm not trying to test the strength of hhg to determine whether or not it's good enough for my application. No, I trust the research and professional experience.</p>
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<p>See, the difference between my Titebond original and freshly made Titebond that's still in the factory is very small. I trust that they have high quality control and test batches of glues before they pack them in bottle to ship out.…</p>
<p>Thanks David, that's a really informative reply. However, this isn't what I'm asking. I'm not trying to test the strength of hhg to determine whether or not it's good enough for my application. No, I trust the research and professional experience.</p>
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<p>See, the difference between my Titebond original and freshly made Titebond that's still in the factory is very small. I trust that they have high quality control and test batches of glues before they pack them in bottle to ship out. The glue in the bottle of Titebond that I have is nearly identical to what's in the factory right now. The only significant difference is that mine is older/spent more time on a shelf. Moreover, Titebond (and superglue and epoxy) is very easy to apply. It's idiot-proof - you brush it on, you clamp it up, and you go about your day. There's no mystery to it.</p>
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<p>Neither of these things are the case with hot hide glue. The glue I'm about to brush on a piece of wood is very different from the glue that's currently being manufactured. I'm sure they have their own strict QC and they test batches, but the fact still remains that I introduce a lot of errors. I cook the granules, and while cooking it isn't rocket science, it still introduces possible errors, whether they're human errors or equipment errors (like a bad thermometer). But not only that, the application of the glue isn't as easy as with Titebond. It gels quickly, and if the clamps don't go on before it gels, or if the piece move around as you clamp, then the joint could be compromised. These are the things I'm testing. My cooking of the glue and the way I apply it. What I'm <em>not</em> testing is whether or not the glue is suitable for gluing guitars.</p>
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<p>Russell answered my question. If I glue things correctly, when I break the joint, the % of wood tear should correspond to what's given in the paper he attached (%59.82). This test is good enough for me.</p> Good article - I love tests w…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1383992014-10-14T11:57:30.750ZRobbie Collinshttps://fretsnet.ning.com/profile/RobbieCollins
<p>Good article - I love tests with <em>p</em>-values! One unmentioned factor is shelf life, both for bottled hide glue and pre-prepared HHG (refrigerated cubes, etc). I assume that, if Winterthur is this methodical, they also have protocols for labeling, shelf-life, and disposal.</p>
<p>Good article - I love tests with <em>p</em>-values! One unmentioned factor is shelf life, both for bottled hide glue and pre-prepared HHG (refrigerated cubes, etc). I assume that, if Winterthur is this methodical, they also have protocols for labeling, shelf-life, and disposal.</p> Thanks David,
I flew test and…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1383342014-10-14T05:39:03.350ZRussell Vancehttps://fretsnet.ning.com/profile/RussellVance
<p>Thanks David,</p>
<p>I flew test and evaluation in the military for part of my service (30 years, 5000 hours total P3B/C) and have experience in failure mechanism both in mechanical bonding and adhesive bonding - particularly long term high cycle/high stress fatigue fails (accumulated "micro fails"are part of this, and you refer to them specifically). This is not to show-off knowledge - it's just to establish my rights to speak to the subject. </p>
<p>Thanks for words on the subject to all…</p>
<p>Thanks David,</p>
<p>I flew test and evaluation in the military for part of my service (30 years, 5000 hours total P3B/C) and have experience in failure mechanism both in mechanical bonding and adhesive bonding - particularly long term high cycle/high stress fatigue fails (accumulated "micro fails"are part of this, and you refer to them specifically). This is not to show-off knowledge - it's just to establish my rights to speak to the subject. </p>
<p>Thanks for words on the subject to all concerned: I was copping a hiding for trying to explain just how complex this subject is or can be. My glue testing regime presented was a 101 attempt to at least get the the subject somewhere near useful for a inexperienced starter.</p>
<p>We build guitars for the commercial marketplace and our reputation depends on our performance and build quality. We do not test the glues we use - we rely on outside agencies or the maker to do this. </p>
<p>Thanks bloke,</p>
<p>Rusty. </p> Testing glue joints like this…tag:fretsnet.ning.com,2014-10-14:2177249:Comment:1383872014-10-14T04:52:39.978ZDavid Collinshttps://fretsnet.ning.com/profile/DavidCollins
Testing glue joints like this is a noble effort, but when looking at the big picture of how it will perform in application, should be taken with a grain of salt.<br></br>
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It's an inconvenient fact that forcing a test joint to complete failure often does a very little to appraise properties over long term use. Testing to failure under temperature or humidity extremes may offer a bit more insight, but still neglect the critical real world factors of cyclical stresses over time (time is a…
Testing glue joints like this is a noble effort, but when looking at the big picture of how it will perform in application, should be taken with a grain of salt.<br/>
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It's an inconvenient fact that forcing a test joint to complete failure often does a very little to appraise properties over long term use. Testing to failure under temperature or humidity extremes may offer a bit more insight, but still neglect the critical real world factors of cyclical stresses over time (time is a critical factor with direct influence which is too often forgotten).<br/>
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I can glue up several identical test pieces with hide glue, PVA, epoxies, superglues, and all sorts of others, and when forced to immediate rupture get surprisingly similar failures depending on the type of test. Glue up a piece of ebony cross grain to spruce, then put it under near continuous high stress for 20-30 years of cyclical temperature changes with occasional extremes, repeatedly cycling through different expansions and contractions as it goes through constant humidity fluctuations. Subject it to millions of vibrations and flexing of the plates, cycle the load up and down over and over, give the occasional moderate shock now and then, and in the real world the strengths and weaknesses can be appraised in ways no simple test can consider.<br/>
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The adhesives will weather these conditions and cyclical changes much differently. Some that are too rigid and brittle may fatigue under cyclical stresses and fail much more quickly. Others with just a bit of elasticity may see less fatigue to a point, by too much and they could exhibit creep over the decades (even though this would never show up accurately in immediate failure tests where time was not tested equally to force). Some may fair well in brief periods of temperature or humidity extremes but suffer in repeated cycles of shifting between more moderate changes. The list of course goes on and on as to what is beyond the scope of simple abrupt failure tests, so while insightful to a point, they should not be taken as any final word.<br/>
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Then of course when you take the view of long term preservation, it must be accepted that all joints will eventually fail. Some may take a few decades, others a few generations, but sooner or later every joint under stress will give. If you are concerned with preservation of what could become heirloom artifacts, then it is worth considering the serviceability of these joints when they do.<br/>
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This (along with many other properties) is where hide glue has a distinct advantage. When a non- natural adhesive such as Titebond fails, the saturation layers left on each face of the joint are spent - all the hydrogen bonds the glue uses to create a proper joint are taken up with an essentially inert dried polymer, and new glue applied to these contaminated surfaces will never form a bond comparable to fresh clean wood. When reglued then, material removal is inevitably required to get past the contaminated saturated layer down to fresh fibers. How deep the saturation goes, and how frequently the joint needs to be serviced (bridge joints reasonably expected a few times each century) will factor in to the usable life of the instrument.<br/>
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Protein glues like hide glue however, are more friendly to less invasive service. Although the saturated areas will contain a lot of broken strands of collagens (kind of like a lower gram strength hide glue), they will still retain the ability to rebond with new glue in a serviced joint. Therefore unlike PVA glue, you can still achieve a very good bond without having to fully remove the saturated layer of fibers, and prolong the life of the instrument by allowing periodic service to be performed without removing significant material each time.<br/>
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Glues are indeed complicated, and testing them perhaps even more so. Not trying to persuade what you should use or even to explain the pros and cons of the varieties. Just saying it's more complicated than what a simple catasrophic failure test can reveal, and they don't tell the whole story of how performance will compare in the field.