Befuddlement??? -Reply

[Delwin D Fandrich]

Stephen Birkett wrote:
> 
> > ...creep is greatly exaggerated. Wood itself, especially spruce, has as
> > much creep as a thin glue line of Titebond II.
> >
> Eh? Wood does not creep...defined to be continuos shear movement over a
> sustained force. Aliphatic resin glues (as far as I know all of them)
> exhibit degrees of creep, where molecular links are re-arranged as a
> response to the applied shear over time. Hide glue exhibits ZERO creep after
> curing. With this definition the wood itself cannot creep!

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. 


> > As far as the “resonant frequency” of either is concerned; surely this has 
> > been shown to be of no practical consequence in any real piano assembly 
> > or structure for some time now.
> >
> The forces involved in the hammer/string contact period are very large...a
> reasonable difference in the compliance of the glue joint could translate
> to an observable change to the overall impedance from hammer to string.
> It would probably be a simple matter to test cured aliphatic glues Vs
> cured hide glue to see if there *is* a difference in the compliance of the
> glue itself...but remember there is a difference between the molecular
> bonding that occurs in a good glue joint (cohesion), and the bulk cured
> glue itself. However I suspect in the real world a large percent of even
> the best glue joint is not molecular bonding, but adhesion...to which the
> bulk glue compliance property would apply. (A true cohesive glue joint is
> not "thin", rather *very* thin, being of molecular length.)

As I said, at one time I did try to prove this—indeed, I wanted to prove
it—but couldn’t. What “could translate to an observable change to the
overall impedance from hammer to string” simply did not translate to any
observable or audible change or difference in sound under any real world
conditions I could come up with. The spectrum analyzer couldn’t tell the
difference either. Nor could the human listeners in blind tests in which
they knew what was being tested, but not on which notes or in which
pianos. (Each of three octaves—various hammers in each octave, but all
were found in the same three octaves in each piano—had some hammers
glued with hide glue and some glued with Titebond.) They did know which
octaves to listen to, the same three octaves were treated in each of
several identical pianos.


> > Now, bear in mind that we use a lot of animal hide glue. I like it for
> > many applications. I also am just old fashioned enough to still like
> > working with it. But, please, let's not romanticize it beyond its
> > capabilities or its usefulness.
> >
> The bottom line is that hide glue is capable of doing well everything
> required in traditional piano building methods...no possible argument
> about that.  

Sorry, but there is much to argue with about that. Some day when I have
more time I’ll go back into all of the reasons—I’ve written on that
subject in the Journal as well, although it’s been some years now...


> Aliphatic resins may be able to do the same as well as hide
> glue, but the jury is still out on that...

How long does the jury have to be out? I’d say that the millions—if not
billions—of wood joints reliably made with aliphatic resins each year
under widely varying conditions by workers with widely varying skill
levels should count for at least some level of proof. 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.


> I would rather stick to the
> tried and tested product. For modern manufacturing techniques hide glue
> may be less practical, or even inappropriate, but for traditional
> woodworking it is by far the simplest and most practical product, if you
> know how to use it correctly...I see no reason to use something else.

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.

--ddf