Official Luthiers Forum!

I do have some interesting news that is upcoming, but first... my question:

As a result of shipping a solidbody electric guitar, have you every seen any kind of joint separation or finish imperfection? I have a project running at work related to this, and I've always appreciated input from this group. The client is worried about Titebond Original joints holding up less well than those assembled with Titebond 50, because the latter has better thermal resistance at elevated temperatures. I have a test series planned out, and my office sure is going to look cool full of guitar bodies for a little while... Aside from the top of a D-45 I have on my wall signed for me by CF Martin IV! Any input is appreciated, and I already have the lab testing lined up (yes, I love my job although I would love to eventually move over to R&D in the guitar industry.)

Now... The fun stuff. I've been collaborating on some acoustical studies, and plans are in place to start learning the truth about how much dampening is caused by adhesives. Most of this shouldn't be earth shattering because our ears don't often lie. However, some of the existing wisdom about wood selection appears it could be turned on its' head from preliminary results. When the report is done it will be publicly available and I will make sure to share it with everyone here.

As always, feel free to contact me with adhesives questions. For my typical full disclosure, I am a technical specialist with Franklin International (the makers of Titebond.) Most posts here are outside of my official capacity, but I'm always happy to help and love talking about and working on guitars!

Thanks for your input!

I always told my clients that the wood used to be alive, and it's still trying to react to humidity and the rest of the environment just like it did when it was still a tree. It's breathes, expands, contracts, stretches, warps, etc..... it's to be expected.

If you wanted something stable buy a Steinberger.

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

Hey, how exactly does Titebond 2 work, on a molecular level, and exactly how much glue is really necessary?
I have my ideas but it seems you might really know.

_________________
Old growth, shmold growth!

I've not seen any joint separation, per se. That would imply exposure to some pretty high temperatures, very high humidity, or both). However, sinkage of the finish over glue joints is quite common, as are "steps" in the finish at glue lines resulting from component slabs of wood moving differently. In my experience, these rarely crack the finish, but with highly polished surfaces they are quite easy to see. I doubt if a move to Titebond 50 would make any difference.

RE: your acoustic tests, if I can help, please let me know!

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

http://www.goreguitars.com.au

Hugh -

I've not seen you here before, but you seem someone I would be much interested in communicating with - I'd be happy to share what I know in exchange for what you know.

As to your first question, of course there are a lot of specifics these things could depend on. Typically, no, if an instrument is well packed it is rather uncommon to see joint failures and very uncommon to see finish imperfections directly related to the shipping.

As to joint failures, that sounds like more of your area of expertise than mine, but I would offer these ideas (which I'm sure you're already aware of). First, "shipping" is best thought of as a time frame in the instrument's life rather than an event. When troubleshooting problems, you of course have to speculate on what particular event or circumstances it may have been subjected to during that time which could have possibly caused (or at least catalyzed) such failures.

The most likely conditions leading to glue joint failure during shipping would be shock or heat. The type of failure between the two would of course be obviously different, so I guess that all I could say is that we would need a bit more information about the type of joint and in what way it failed to offer much help. In general though, no. If a guitar were well packed and not shipped during extreme heat conditions, glue joint failure is quite rare. Wood fracture is much more common due to extreme shock and/or poor packaging than glue joint failure is.

As to finish imperfections, again, more details about the imperfections and shipping time/environment could be helpful. Finish cracks (from stress), checking/crazing (from cold), blushing (from moisture/humidity), dents/dings (impact, poor packing), softening/impressions (incomplete curing, contact with incompatible plastics/vinyls)? Lots of things could happen to a finish, but without more details it's difficult to suggest which primary suspects first deserve investigation.

As to the acoustical studies, I'm all ears. You may be acting kind by saying what you have, but I would suggest a few other things. First, -


Let's face it - our ears do lie to us. They lie like crazy. Hearing is a sense, and just like sight, taste, smell, our mind can process what we hear in some ways that perform incredible tricks with our perception. Penn and Teller could have just as much fun with auditory tricks as they do with visual ones if they wanted to, because our ears do lie. Hence the importance of well controlled blind testing.

Second -


Much of the existing wisdom about wood selection is well earned, vetted, and proven reliable. On the other hand, much of it is also old wives tales and Ptolemaic astronomy, conclusions drawn over years of correlation, though without much reliable evidence for direct cause and effect, and therefore undoubtedly riddled with errors. This old knowledge is valuable, but no doubt stands much room for advancement in understanding.

Of course I would advise you to be careful in your conclusions to consider the controlled limitations of whatever tests you may perform. You may find damping or transmission properties to be different than what was previously believed, but this alone may not directly lead to conclusions of better or worse for an application. Perhaps some have claimed to prefer one wood or adhesive over another, and incorrectly attributed this preference to lower damping. Your tests may show the change to actually provide for higher damping. This may do little to change preferences of what ultimately sounds "better" though, but rather simply expose the inaccuracies of prior explanation attempts at what the underlying causes of differences were.

Sorry for the long winded post, but your studies intrigue me, and I am very interested in keeping in touch and up to date with what you are exploring. I have many industry specific suggestions for testing properties for which I have not been able to find data, and also been unable to conduct controlled enough experiments on my own to satisfy. I've spent many years studying and experimenting with adhesives, reading textbooks and publications, experimenting with many natural collagens and additives as time allows, but this time is of course limited to a hobby. Having the ear of an insider such as yourself, with hopes of gaining some knowledge, sharing ideas, and perhaps even influencing possible tests - I have to be honest that the idea of continued communication excites me a bit.

Please keep in touch, please share what you can, and I greatly look forward to reviewing the results of your research.

_________________
Eschew obfuscation, espouse elucidation.

Yep, I know everything from its' mechanism to its' formulation! You're right on the edge of asking for trade secrets too. Titebond II is a catalyzed (cross-linking) PVA, which means that aside from simply drying to build strength it also undergoes a reaction catalyzed by aluminum chloride. This effectively makes the dry polymer into a web like structure containing countless irreversible bonds which impart water resistance. I seldom recommend using Titebond II on guitars except under very special circumstances because ANSI/HPVA type II water resistance should never be needed by a musical instrument. In order to formulate a one part cross linking PVA, tradeoffs are made in other areas of performance such as thermal and creep resistance, which are among the last properties one should sacrifice on an instrument. If you absolutely must use Titebond II because you have a big factory and use RF to accelerate your process (and there are a few major companies I know who do this) at least use Titebond II instead. It contains some wood flour filler that makes up for the losses and then some, and you pick up a big increase in working time

Let me know if my answer was too technical and I can explain it another way.

Trevor-

I agree with your assessment. The only risk comes from moisture problems that will create internal stresses in the wood to begin with. Combine this with high enough temperatures and something could happen, but it's extremely unlikely. The testing I have scheduled should prove the point nicely that under these circumstances a joint assembled with Original is no more likely to have problems than one assembled with 50. My main question is if anyone has ever even seen it happen in real life. Actually, even steps are a result of moisture.

I have several wonderful PDFs on acoustics studies for which I am seeking permission to distribute by the author. The method being used turns the guitar top into a speaker cone. I have ideas to perfect it for lab use and any information along these lines will be shared. Also, if anyone ends up deciding they have sufficient time and resources to conduct tests, I will be happy to provide adhesives for testing.

I'm a pretty big fan of research over speculation, so count me in as excited for the results.

As a semi-related question, have you guys ever done any exhaustive testing on clamping pressure to determine what 'enough' is and what, if it exists, 'too much' is? I'd be interested in seeing the results and methods for sure, or even hearing what your 'standard' is for measuring the joint strength so I can use a similar setup in my own tests.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I don't understand this sentence. Which Titebond should I use (if forced to) for instrument applications? Does Franklin make a better glue for instruments?

Also, how thin can I coat the surface and still get a good bond? Should the wood surface just glisten, should it be opaque? What is the bare minimum amount of glue I can use and get away with it?

_________________
Old growth, shmold growth!

I've had some one leave a bass I built in a car all day at an out door gig. I repeatedly told her not to do it but she did anyway. I was surprised to see no damage and it was built with all Titebond original. Maybe if it was left in the trunk with no air flow through windos it would have completely melted. I've definitely seen the results of that in my repair shop. But suffice to say I think under normal situations TB is good stuff just don't cook with it.

Would love to see the results and methods of your experiment too.

Yes we have, and what we learned is that it is impossible to create a starved joint using PVA wood glues. Starved joints are easy to create using hide glue, so concern over this topic carried over as PVAs gained widespread acceptance in the woodworking world. We have tested clamping pressures in excess of 425 PSI, which produced a perfect joint. The only limit for clamping pressure is the compressive strength of the wood. Once you start crushing wood fiber too much pressure is being applied. Depending on the modulus (similar to rigidity) and thickness of the wood, some species can take tremendous pressure. Clamping has everything to do with bringing the bonding surfaces as close together as possible, so if the surfaces are perfectly mated to being with it is more likely that optimal strength will be achieved even with less pressure.

We measure bond strength using two Instron universal testing machines that are rated to 20 tons each. These run about $85k each, and you really don't need anything close to this for testing joints at home. A good glue joint will be stronger than the surrounding wood, so even hitting a joint with a chisel and hammer can tell you everything you need to know as long as the wood fails. I have some ASTM D905 tests coming up soon, which is our standard shear strength test. If there's interest I can take a few pictures.

Whoops, I meant to say Titebond II Extend (corrected above.) The two best products generally speaking for guitars in our product line are Titebond Original and Titebond Extend Original. I use Titebond Extend Original for all of my guitar work because it has a slower speed of set (more working time) and otherwise has the best performance characteristics of any PVA in our line aside from its' lack of water resistance. Even at 150°F it can lose as little as 15% of its' strength. That ends of translating to excellent creep performance. Since it contains some wood flour as filler, there's even wood material inside of the joint which is a big part of why it performs so well. It's one of my personal favorite products for very good reasons.

David-

Thanks for the input, what I will be testing is effectively a non-issue in my mind but when clients start talking about millions of dollars in product tests are in order! I was curious if anyone has ever actually seen a solid body fail in any way from heat encountered during shipping, or even in the trunk of a car.

Many of our ears are pretty accurate, it's our interpretation of what they tell us that tends to be questionable. I am seeking approval from an author to share the information he has shared with me (he'll probably be cool with it.) However, I agree that there is much to learn. Since development isn't technically in my job description I'm actually developing a new class of adhesives at home with my own resources, which I anticipate could offer ideal characteristics for many applications. Finally measuring the acoustical dampening imparted by adhesives will be groundbreaking information for the guitar world. I think there's a lot of room left for science in this particular art.

We'll certainly be in touch.

Thanx!

_________________
Old growth, shmold growth!

I've seen plenty of heat related joint failures from instruments left in cars on sunny days - Just the other day I had to replace a bridge on a Guild that slid nearly 1/8" forward (sheared off the pickup wire) from being left in a storage unit that got too hot. I don't recall seeing any such damage during shipping though. I'm sure it can happen, but this is one of the reasons I always recommend shipping on Mondays, so they don't run the risk of sitting in storage over long weekends.

I agree that there's a lot of room left for science in this art, but you'll be meeting a rather tough crowd when challenging "conventional wisdom". Of course quantified tests of damping properties is the easy part. Qualified testing is where it gets tricky. True blind testing is imperative here, and of course good practice in controls and record keeping. Avoid jumping toward descriptive qualities or preferential (subjective) judgements, and start just by identifying what change is required to establish a difference limen, or minimally noticeable effect.

My favorite method for such listening tests is simply the "odd one out" method. Take a number of samples, several set up identical to each other, one with a singular alteration (different adhesive in your case). If you have three samples with hide glue and one with PVA, with consistent signals being transmitted to/through each, the listener's goal would be simply to identify the odd one out (preferably being able to listen to the different samples consecutively in real time). Randomly rearrange the order of the samples and repeat the test even just a few times, compare the survey results against statistical random odds, and it's not too difficult to establish whether any difference can or cannot be reliably heard.

The beauty of this simple method is the absence of metaphorical descriptions of tone (words for which listeners can assign quite different qualities), and refraining from asking for a preferential judgement of better or worse. Those polls can follow later, but first you must establish what amount of change is required for any difference to be noticeable at all.

I'm probably spewing out things you already know about, and I'm sure you already have some well planned tests in the works, but forgive me if I do that a lot. Howard Wright has an excellent chapter on testing procedures for listening tests in his dissertation "Acoustics and Psychoacoustics of the Guitar", which I believe he has made freely downloadable online.

I look forward to reading your colleague's article if you can make it available. Has it been published anywhere else yet? I've read some articles related to damping or vibration fatigue related to adhesives, but they are often focused on materials, frequencies, and forces well outside our direct areas of interest, such as architectural, automotive, or other more industrial interests.

_________________
Eschew obfuscation, espouse elucidation.

If I may butt in with one more thought - I have never assumed a great deal of credit toward tonal effect on damping properties of adhesives, so long as the joints themselves are well fit. Of course if you glue your bridge on to a shelf of finish around the edge as most makers do, leaving a nice 4-6mil pad of glue between the bridge and top then of course it may have more effect (both tonally and structurally given the lack of gap filling strength of most adhesives used here). If you fit the joints properly though, well mated wood to wood joints, I have always held doubts that the type of adhesive could create a very noticeable difference in tone.

Of course these conclusions are surmised only from seemingly sound reasoning, but still admittedly conjecture to some extent, and lacking in any proper testing to back them up.

My priorities lie much more with issues such as durability, fatigue resistance through cyclical changes under load, and of course serviceability in the future, compatibility with re-adhering separated joints without having to remove all material saturated with adhesives in the past. If saturating a surface with an adhesive which once cured will not bond well with subsequent reglues, then this does not bode well for preservation of heirloom instruments over many centuries of inevitable service.

I've played around a lot with collagen adhesives for this reason, like of course hide and rabbit skin glues, adding fish glues and fish collagens, playing with propolis as both a tackifier and antimicrobial additive (it seems to work exceptional for this), things like alum and formaldehyde for moisture resistance, of course urea additives and so on, but it's only been a casual hobby and I've not dabbled much in synthetics (aside from playing with a polyvinyl alcohol mix with collagens, for reasons I honestly can't recall now).

The ability to reactivate prior adhesives and form suitable bonds on repetitively serviced joints however is a very key factor in my interests. I'm sure this topic is but one among many which are quite different from your current research interests, but I'll keep throwing them out there anyway. The next big test I'm hoping for is of fatigue under load through repetitive cyclical changes. I'll probably use the bridge scenario - resinous hardwood bar glued with growth rings perpendicular to those of a spruce top, under constant load, subject to repeated 48-72 hour cycles of extreme low and high humidity (maybe I'll play with temperature after this). Forced failure of fresh glue joints doesn't always tell the whole story of how they may respond under real world conditions. I'm still looking for the right sized environmental chamber (they come up for sale from the University up the road all the time) to conduct these tests in, but I do hope to get to it one of these days.

_________________
Eschew obfuscation, espouse elucidation.

And epoxies! (don't ask how I know... )

_________________
Eschew obfuscation, espouse elucidation.

Can you give us any insight into what property of hide glue makes it prone to glue starvation? I think of glue starvation being more of a joint geometry problem (and maybe a glue viscosity problem), than a clamping pressure issue. Tenon joints, for instance, will do a good job of wiping all the adhesive off the gluing surface if the joint is nicely made.

To your original question: you asked about finish damage in shipping. I don't think you'd be interested in stories about the French polish finishes I've seen damaged by heat. Still not an adhesives issue, but I refinished a poly coated guitar that got lost for two weeks in a New Jersey cold snap during shipping. Large (3x4") flakes of finish were lying in the case near the corresponding bare wood patches on the guitar when the case was opened. Big name American manufacturer, but it was clearly the shipper's fault, not the builder's.

One last question (and a plug for your products): I've repaired a lot of bone tie-block caps that came loose from the bridge. The standard narrow strips are pretty well supported, but the one piece caps like Torres used can shear off the rosewood under string tension. I talked with the builder about surface preparation, and he tried scraping new surfaces, as well as acetone wipes, and soaks. Cyanoacrylates failed, and PVAs failed. I did some tests, and was surprised to find that Franklin liquid hide glue worked better than everything else I tested. (Yes, the glue that luthiers will only use for labels, and yes, much better than hide glue. Okay, I didn't try fish glue.) He switched to liquid hide glue, and has had no further failures. Any pointers on glues for this application?

I did some tests to determine the proper amount of pressure required to minimize the glue lines between the laminated plates of my electric bodies. If you recall, my bodies have carved tops which cuts through a facing layer to reveal a contoured band of the sub layer. Since the carving has such a shallow angle (5 degree) in some places, the glue line must be minimal or the shallow angle will accentuate it.

The tests were based upon a series of small, laminted test panels that were clamped into a Kurt vice. Those vices have published clamping force data given at specific torque settings. I determined the ideal amount of pressure was 250 p.s.i. ....quite a bit really. Once that was determined I had an engineer do a stress analysis on various thicknesses of aluminum plate to determine the right thickness to use for a hyrdraulic press that I built to clamp these plates. I get a very consistent result with that glue line now.

Imo...there's no such thing as too much pressure unless it exceeds the compression strength of the wood.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

That's been my experience as well, and I also did tests in a Kurt vise. I made some tall jaws to use it more effectively as a clamp. You go about most of your work in a very similar way to how I do things, though I haven't had time to share much here. Probably a result of having machining and composites backgrounds, I suppose. I've done tests with CA, fish glue, and PVA in the vise and also a hydraulic press with no failures, but I'm hoping I'll get around to doing some more methodological tests. I'll get around to doing some tests with hide, I just didn't happen to have a batch mixed up when I was doing the tests.

I think Eric is correct on the cause of most, if not all, 'glue starved' joints. It's much easier than most people think to have the clamping pressure in a joint go up and then back down as clamps and cauls are being applied, which first squeezes out the glue and then opens the joint back up in that area. There's insufficient glue in the joint, or glue curing too soon, which can both happen easily with hide or CA, but those are pre-joining errors.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I probably should add that I use epoxy in any situation where the joint is critical in terms of time. Given the long open and cure time of epoxy, relative to other glues, there is ample time for pressure to evacuate all excess glue before a set begins. I couldn't possibly control the glue line between these panels with any other kind of glue.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

The theory isn't perfectly established regarding why some adhesive types are more prone to starvation than others. I can go into some depth on theory but adhesives are largely understood through trial and error testing. Much of what causes joint starvation is related to pressure and the rest is how the adhesive behaves during strength development (reaction, protein folding, etc.) Most of what I can offer is still conjecture at best. When it comes to starved joints the two biggies have already been hit on: hide glue and epoxy.

BTW, as long as it's fresh TB Liquid Hide Glue is much more capable than most people give it credit for. It's a room temperature stabilized 250 gram strength hide glue with better creep resistance than any PVA. Hide glues are at least as capable as modern PVAs aside from moisture resistance.

So somehow this post re-emerged in my head the other day - I just bought a vacuum pump for vac fixtures on my router but, I figured I could use it down the road for other things such as bagging and stuff.

250psi is a lot more than the 13 or 14psi you get with a vac setup....does this mean we can pretty much forget about bagging to join parts with PVA, or just that we'll have a big glue line?

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Personally, I'm pacing the floor impatiently on this one. Titebond Original is my "go to" adhesive, and I'm anxious to learn what testing will reveal about its sound dampening qualities.

_________________
David Morris

I'm a little more concerned with cold creep, lately.

Hey Hugh, what say you? Does Titebond Original Extend creep? For that matter, how serious an issue is cold creep with regular Titebond, especially when compared with your hide glue?

_________________
Old growth, shmold growth!