Engineering vs Seat of the Pants

[Erwinspiano at aol.com]

Ric
  If you are looking for some kind of numbers I can't help  you but if you 
want my tactile experience.  That's another.  The  assumption that CC boards 
aren't strong would be incorrect.  They are  extremely strong due to there non- 
linear compression rates.  meaning as  they are compressed they become more 
resistant to compression by the bearing  load.  Also Sitka spruce renders them 
even stronger because of its  strength.  AS has been said before that drying the 
panel will create  compression as well as the steepness of the soundboard 
press/dish it is being  pressed in. 
    My Colleague Chris Robinson of Connecticut  still produces a C. C. Board 
& as you may know from the Mason & Hamlin  on display in the rebuilders 
gallery, his boards sound really good.    You may wish to ask him some general 
question but other than that he is  rightfully proprietary about his methods. I 
will tell you he uses different  radii cauls for different sized boards, if that 
tells you anything. If you think  about this a bit you'll figure it out.
  If you get an opportunity to restring a C. C. board with  a fat crown try 
pre stressing it & you'll find out in a tactile sense just  how stiff they can 
become very quickly.  Also I suspect it is this  predictable quality that 
makes it an easy method for the factories to use. In my  experience a C.C. board 
coming from the usual places will always sound better if  I can spot some 
compression or compression ridges in the panel. Ie. the Yamaha  C-7 F I tuned 
yesterday.  I've worked on it 15 years & it's Best one  I've heard.  It has 
significant and visible compression in the panel &  more than most Yam's
  Dale

Hi  folks

One thing that keeps bothering me and makes it difficult to  resist 
buying right into the RC & S gangs reasoning is that we never  hear 
anything about how
compression reliant boards  figure load  bearing.. or much of anything 
else for that matter.  I find all kinds  of references to how an RC & S 
board is actually designed... but  nearly nothing about how one figures 
basic things like just how darned  strong a CC board is. 

It struck me the other day that perhaps there  isn't really much to begin 
with, that perhaps this all was started by a  more seat of the pants 
approach.  If you dry a panel you can judge  its MC fairly accurately by 
knowing the beginning MC and how much it  shrunk after drying ... yes ?  
So.. reversing that logic if you have  a dried panel and inhibit by some 
mechanism it from expanding and you know  how much increase in RH you 
subject it too... then you know how much  compression the panel has taken 
on.  Ribs are a way of inhibiting  this expansion yes ? Seems to me then 
that measuring the amount of crown,  knowing the bending strength of the 
ribs, and the change in RH gives you  then enough information to fairly 
accurately find the strength of the  assembly for any given amount of 
crown. From that point perhaps a few  decades of trial and error with 
regard to problems incurred with various  rib placements designs was more 
significant in terms of  <<design>> then any engineering in the usual 
sense of the  word.

Ok.. this is pure speculation on my part.   But it  would REAAAAALLLLY be 
helpful if someone would do a basic review for the  benefit of the whole 
list as to how one goes about designing (by the  book... if there is one) 
a CC board, or any board that relies very much on  compression.  It would 
most certainly make it much easier to  see  <<the light>> as it were 
between the various methods  of building boards.

I've done two board replacements earlier... and got  quite a bit of 
advice as to rib placement / size... etc... and both these  were reliant 
on compression for crown... and no one could really give me  any good 
specific engineering reasoning's for any of their  advice.

Cheers
RicB


 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20061216/dd7af488/attachment-0001.html