laminated ribs

[David Love]

I see.  By larger piano do you mean a D?  Or are you going up to 900 lbs
for, say, a B as well?  You mentioned previously that you are building the
ribs for higher load than you started originally and you found that there
was some relationship to hammer tolerance.  The boards that you are now
building that are set up for, say, 650 lbs, what would those have been
previously?

Just as an aside, you said that you plan for 40% deflection and end up
somewhere between 40 and 50%.  I assume you are calculating your deflection
from beam formulas and basing it on the rib properties only and ignoring the
panel in the calculations, for the most part.  It's interesting that when
you calculate for deflection based on the ribs only that the panel itself
contributes very little if anything to the stiffness of the assembly in
terms of the overall deflection.  Do I understand that correctly?

David Love
davidlovepianos at comcast.net 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Saturday, March 25, 2006 8:22 AM
To: Pianotech List
Subject: Re: laminated ribs


> Ron:
> 
> I just want to revisit this for a moment.  Do you mean your typical load
is
> 900lbs?  And if so, what kind of deflection are you building your ribs
for,
> i.e. what percentage of the original crown do you figure is remaining
after
> the board is loaded?
> 
> David Love


David,

Somewhere in the vicinity of 900, in a big piano. I'm figuring 
1° in the bass, up to something between 1.5° and 2° at the 
top. I calculate for about 40% deflection in design, and wind 
up between 40% and 50% in reality. I'm happy with at least 50% 
of the original crown remaining. A smaller piano with fewer 
ribs might get more like 600 or 700 lbs, with bearing angles 
adjusted accordingly. Since the spring rate of rib supported 
boards is much more nearly linear than in panel supported 
boards, small changes in bearing angles don't have dramatic 
effects on tone, so the whole thing becomes more structurally 
and less tonally oriented.

Ron N