creep creep creep

[John Hartman]

Stephen,

I have been following you discussion of "creep" with some interest. I 
would like to add a comment. A few years back at the New York PTG 
Conference the wood technologist R Bruce Hoadley presented a class on 
wood technology. After the class I had the opportunity to ask him some 
questions one of which related to the effects of time dependant 
deformation. He stated that any wood component under load, however small, 
would continue to deform (creep) until failure. He used a hypothetical 
experiment to illustrate his point. Place a wood sample in sealed room 
with no oxygen (to eliminate the effects of oxidation and with no 
bacteria. Place the sample between two stone supports. Given an ample 
amount of time the wood beam will sag more and more, under it's own 
weight, until it breaks. This experiment has never been executed but 
observations and theory support these conclusions. Dr, Hoadley pointed 
out that no accurate predictions could be made to the amount of time it 
would take, only that we know it will definitely happen. This is the case 
because the creep gradient is so sleight and no experiment has progressed 
long enough to plot the curve (and I might add the answer has no 
practical application). It was also suggested that the effects of time 
dependant deformation are greatly accelerated if the wood is subjected to 
loads close to the plastic limit.

I believe I have seen many examples of "creep" . Wrest planks that twist 
far enough that the action can't be removed (1860s Steinway and 
Chickering grands). Oval tuning pin holes (just about any piano). Flat 
soundboards (most modern pianos). Vary old and plane old twisted squares. 
Twisted trebles on early grands so bad that the bass leg points to the 
zenith while the treble leg points to the north star (Beethoven's 
Broadwood is looking pretty sad). Sagging beams and joists in old houses. 
The dropping shoulders of old time piano tuners. Sagging interest in 
tired old pianotech debates. Any way you look at it time is against us, 
nothing last for ever. Thank God, some things are just not worth a second 
time around.

Stephen, You have repeatedly reported the remarkable durability of 
soundboards in early pianos. You have attributed this fact to the thin 
finish and the use of hide glue but is it possible that earlier pianos 
through design and circumstance are less stressed than modern examples? I 
think this is so when comparing antique and modern soundboard designs. 
Without getting into a long debate on soundboard construction let me list 
some casual observations. Modern soundboards have considerably more crown 
than any antique examples (about 5/8" on a 48" long rib at 7% EMC). 
String down bearing loads are considerable 1000-1500 pounds or more. 
Modern cases are very ridged and do not move when the soundboard expands 
with increased humidity. The across the grain measurement is around 50" 
on modern pianos while considerably less for your antiques. Antique 
soundboards are thin and have smaller ribs which may allow the board to 
relieve the stresses of seasonal movement better. I am sure you have seen 
examples of soundboards swelling enough to touch the strings. One last 
observation; many surviving example of early pianos have lived in the 
kinder environment of central Europe. Maybe they don't over heat their 
homes or are more diligent about piano service.

Respectfully,
John Hartman

P.S. For the most part I am with you on the Hide Glue issue. I buy my 
hide glue 40 Lb. at a time.