Stephen Birkett wrote: > > Del wrote: > > Wood does not creep? Of course it does. Check the WOOD HANDBOOK, Wood > > as an Engineering Material; US Department of Agriculture Handbook #72, > > Chapter 4; The Mechanical Properties of Wood, Pages 4-4 and 4-36 through > > 4-41. > > Also UNDERSTANDING WOOD by R. Bruce Hoadly; Chapter 6, Strength > > of Wood. > > Also just about any text on the structure of wood or wood > > technology that you can find. Wood does indeed creep under load. > > > Steve wrote: > We are no doubt talking about different things here...I lent my copy of > Hoadley so I can't check what you are referring to by this. Obviously wood > does experience an effect from sustained stress, but I wouldn't call that > creep, at least not in the same sense creep is used with respect to > aliphatic glue joints... I've seen harpsichords (less than a tonne of string > tension) literally fallen apart over time due to aliphatic creep (modern > ones of course), wrestplanks moved forward into the gap etc....to be fair, > these were the older aliphatics, and Titebond is clearly much better in > this respect. But I've not seen any evidence that Titebond creep is ZERO, > as is creep for hide glue. I would have no confidence using Titebond on a > big romantic piano, that sustains up to 6 tonnes string tension, held > together entirely by the glue. I know that hide glue works in this > application. Creep is creep. When any structural material is first loaded—whether it be a wood beam or a glue joint—there will be some, albeit in the case of animal hide glue, very slight, elastic deformation. If the load is maintained for a period of time there will be some additional time-dependent deformation. That is creep. And it doesn’t matter if it occurs is a wood beam, a soundboard panel or a glue joint. Actions, whether ancient or modern, are subjected to stress loads of such short duration that they are essentially unaffected by creep. But the evidences of creep have been visible to some extent in every wood framed fortepiano or harpsichord I have ever seen. Creep in the wood structure is what has caused (perhaps “allowed” is a better term) them to buckle—however much or little that may have been—over time regardless of the adhesive used. Creep, or its cousin, compression set, is also the primary culprit in probably 99.9% of all soundboard failures that cannot be attributed to glue failure—at least this is true in compression crowned soundboards. Again, this is independent of the adhesive used. > > Del wrote, > > .... Having worked in a > > piano factory that used both hide glue and aliphatics I can assure you > > that there were far more joint failures in the joints bonded with hide > > glue than in those made with aliphatics. > > > Steve wrote, > Two possible conclusions here. Either the hide glue was used incorrectly > or hide glue was not appropriate for the modern manufacturing > techniques/processes used in the factory. One of my objections to the use of hide glue today is that, contrary to your insistence, it is a bit tricky to use correctly. It requires training and experience to achieve consistently good results. Neither of which can be assured in either modern factories or in the vast majority of piano shops of today. Young people grow up today being educated and trained to do many things, but the use and application of hide glue is generally not one of them. If they have been given any woodworking training or experience at all it will have been with the use of either Titebond or Titebond II (or their competitive equivalents). Since there is little need in today’s world for this reality to change, it probably won’t. But in the joints I was referring to, hide glue was simply an inappropriate adhesive for the application. It was being used only out of a sense of tradition. “But, we’ve always done it like that...” Steve wrote, > With traditional woodworking > craftsmanship there are hundreds of years of "proof" of the effectiveness > of hide glue. In the extreme, there are numerous examples of romantic > pianos, with no iron braces whatever, and string tensions upward of 5-6 > tonnes sustained continuously over 150 years, entirely relying on the > properties of hide glue to keep them together (no iron braces > whatsoever)...and they still are. Aliphatics may be able to match this > performance, but we will not be able to confirm in our lifetimes whether > their long term reliability is as good as hide glue. Our shop specializes in the replacement of piano soundboards. The majority of pianos coming to us have soundboards that were made, ribbed and assembled to the rim using animal hide glue. From our perspective, this is probably a good thing. We know from experience that soundboards glued to the piano rim will usually pop free fairly easily with the deteriorated animal hide glue joint breaking cleanly most of the time. Assuming, of course, that the soundboard-to-rim glue joint has not already failed—many have around at least around some part of the rim or belly rail. We also know that it will be difficult to get the old soundboard assembly out of the rim in one piece because, more often than not, many of the glue joints holding the soundboard panel together and the ribs to that panel will have already failed. So much for long term reliability. Again, allow me to repeat my standard caution of using the exceptions—i.e., the survivors—to attempt to prove the rule. I have also found many very old hide glue joints to be in good condition. But I’ve found enough failures to know that I am unwilling to trust any critical structural joint to the uncertainties of animal hide glue. It is personal experience with the stuff that has taught me to question—not respect—the long-term reliability of hide glue. > > Del wrote, > > I have no problem with that. I just object to the implication that hide > > glue is somehow superior to some, if not all, of the more modern > > adhesives. For most applications, it is not. For some few it is as good. > > And, for an even fewer number of applications, it may indeed still be > > superior. > > > Steve wrote, > I agree with you Del, up to a point. For modern cabinetmaking/factory > style construction, hide glue may not be suitable. Apart from such > industrial applications, I see no reason to use aliphatics in the small > shop. Del...for what applications do you think hide glue is less suitable > than aliphatics? > > As I've said many times, hide glue is so much easier to use than any > modern adhesive, why use these messy aliphatics? > > Stephen > Stephen Birkett Fortepianos > Authentic Reproductions of 18th and 19th Century Pianos All adhesives can be used inappropriately. Including hide glue. Granted hide glue has nominal creep, but for that very reason it is a poor choice to use for a lap joint. It is also particularly weak in tension—a fact clearly understood by early piano builders who provided a method of mechanically clamping the ends of the ribs to the rim. They notched the rim and fitted the rib to the notch such that there was actually physical contact between the bottom of the rib and the rim. (This practice later became corrupted so that the notches were arbitrarily cut deep and the excess simply filled with glue.) Hide glue has very poor gap filling qualities. It becomes quite brittle with age, especially when applied in a thick glue line. With age, the brittle glue simply crumbles and falls apart. Hide glue is highly susceptible to moisture damage, i.e., it is not even moisture resistant, let alone waterproof. (While I freely acknowledge that we rarely give our pianos baths, it is not unheard of for them to be exposed to high levels of heat and humidity.) Animal hide glue is at least as messy to work with as any other adhesive—more so than most—and is much more tricky to work with than any other readily available woodworking adhesive. Early aliphatic glues did exhibit a fair amount of creep and thoughtful wood workers understood this and used them accordingly. Modern aliphatics such as Titebond II, MPA II, etc. also exhibit some nominal amount of creep. It is very slight, however, and they have been used successfully for a long enough period of time in bent-laminate structures so as to prove that this is no longer a consideration in any practical application. As I said earlier, any remaining tendency to creep that may remain is insignificant compared to the natural creep found in wood, especially spruce, sugar pine, etc. We use MPA II for nearly everything in our work. Contrary to your assertion, it is easy to use, it is not particularly messy (certainly less so than hide glue), it is utterly forgiving, it is much better at gap filling than is hide glue, it requires virtually no training in its proper use, and it forms consistently stronger bonds than are possible with hide glue. It is also reasonably water and moisture resistant. If the possibility of creep is a factor in determining the type of adhesive to use in a structural wood joint—it rarely is, the joint should be designed to be structurally supportive if possible—we will generally choose a urea-formaldehyde based adhesive (sometimes called plastic resin glue). This is an excellent structural adhesive with many times the bond strength of animal hide glue and one which also forms an extremely rigid joint—it is at least as rigid as with hide glue—but with the additional advantages of being very easy to use, again utterly reliable. It is even more water and moisture resistant than Titebond II and MPA II. We use urea-formaldehyde for many belly work applications. I don’t consider absolute water resistance to be terribly important for piano construction, but if this were to be a property I considered critical for some application—if you intend to store your piano from time to time in a vat of boiling water, for instance—I’d use a resorcinol resin adhesive. This is probably the strongest and most reliable adhesive extant and it is completely waterproof. It will even pass the “boil test”—but, therein lies a tale for another day... My apologies for allowing this to get so lengthy. With this I’ll end my participation in the great glue debate of ‘97 and allow Steve to have the last word if he so chooses. —ddf
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