laminated ribs

[Ric Brekne]

Given the fact that I am about to sink my feet into this kind of thing 
seriously for the first time... I shore nuf would like to see some 
semblance of consensus formed here.  Strikes me that a range of 200 to 
900 lbs of downbearing on the soundboard is a rather huge window. 

Could you guys please go a bit into how each of you arrive at your 
figures ?  And I would also like some words on how typically this load 
is spread over the panel.... along with a few words about how one 
designs ribs to carry the load as it varries over the board.

Also... assuming the greatest load is up in the treble (which I seem to 
have got into my head is the case) how likely is it that given a board 
with grain going perpendicular to the bridge with the longest ribs then 
being in the treble area, would be able to hold up against the minimum 
figure arrived at above.

Thanks
RicB



------------------


Dale wrote
 >/ Ok Now I,lm confused. If were only trying to support only 400 to 600
/>/ lbs. of down bearing force as Del inferred recently or whatever one
/>/ calculates this to be, then what's all the fuss about.
/
My loading of new boards these days is typically half again
over 600 lbs.


Ron, so you are saying a 900 lb bearing load is probably an in the ball park
average plus or minus for various sizes of pianos & string scale tensions.
Then my comment a couple weeks ago about bearing being 1000 lbs or more
depending on who you ask wasn't that far off this figure even though Del
disagreed with that as being "excessive."




Consider a basic scale of moderately high tension. Say 40,000 lbs. 
overall. With
this string tension 1,000 lbs of string downforce equals 2.5% of scale 
tension.
That is quite a lot considering that most companies are claiming string
downforce more on the order of 0.5% to 1.5% of string tension (which 
would be
200 to 600 lbs). I thought I was setting my initial string downforce 
pretty high
at around 1.0 to 1.5%. I don't like thinking about what I'd be doing to 
a board
loading it up to 2.5%. I can't imagine it being happy enough at that 
level to
want to stay there.

Del