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<DIV> <STRONG> Hi Ric</STRONG></DIV>
<DIV><STRONG> I've been gone this week. First, transporting the
little redesigned Stwy O to Alameda for the class, then teaching the class
& visiting with friends, returning piano etc,etc add exhaustion. It's Friday
& I'm glad so I havent' been ignoring this</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>Hi
Dale<BR><BR>This argument about ribs not supporting crown has bothered me from
the <BR>first moment I heard it. And after reading Nossamans well written
<BR>article in the latest Journal I think I know why. Ok, nobody
questions <BR>that in a CC board ribs do not provide beam support for the
load. But <BR>that's not quite the same thing as saying they don't support
load in a <BR>different fashion.</FONT></BLOCKQUOTE>
<DIV> </DIV>
<DIV><STRONG> Hey they add something . If that wasn't true every C.
C. Board wudda caved on inception.</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>
The same thing goes for the crown argument. And <BR>that's where Ron's article
comes in.</FONT></BLOCKQUOTE>
<DIV><STRONG> I'm not sure I know which article this is. I'll
find it. what month?</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000
size=2><BR><BR>About 2 years ago I posted a couple threads with some drawings
trying to <BR>explain why I thought the ribs in a CC board had similarities to
a <BR>cable in the sense that they attempt to constrain the board from
<BR>expanding... so the panel has to bend instead. That very resistance to
<BR>the panels expansion is every bit as much a load support but in an
<BR>entirely different way. What the kicker back then was, was that I tried
<BR>to argue that the ribs strain (note the word usage) against the
<BR>expansion forces from the panel. I was told then that no.. the ribs
<BR>don't strain.... they simply bend against their better
nature. </FONT></BLOCKQUOTE>
<DIV><STRONG> As I read the other posts on " Strain" & I
have to see the ribs being pulled up from there flat orinetation by panel
expansion as ......strain? If some one bends me out of shape I feel
....strained</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>Enter
<BR>Ron's article disclaiming the buttress arch. In that article he
shows by <BR>experiment that the top half of the ribs not only bend, but they
expand <BR>lengthwise. That expansion is critical to his whole argumentation
<BR>(which by the way made perfect sense to me).<BR><BR>But that same rib
expansion shows conclusively that the ribs do strain, <BR>and significantly so
against the expanding panel. </FONT></BLOCKQUOTE>
<DIV> <STRONG> The strain is being initiated by the panel
expansion</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>If you
stop to think <BR>about it this only makes sense. If the ribs can not
strain lengthwise <BR>at all, then neither could the panel crown, yet if they
strained equally <BR>through their height then they would not constrain the
panel at all. It <BR>is because they DO strain ... more on top and
increasingly less towards <BR>the bottom combined with the panels compression
that crown and crown <BR>strength occur. And it doesn't really seem to me to
be so much a stretch <BR>of the mind to imagine mathematical explanations for
all this that <BR>would fit very nicely into design thinking. <U>The
height and width of <BR>ribs don't add up to combine in a kind of beam
strength / mass <BR>relationship... but rather a kind of strain strength /
mass one.</U> </FONT></BLOCKQUOTE>
<DIV> <STRONG> I think I follow you. Frankly it helps me
to think the whole assembly as plywood</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000
size=2><BR><BR>One thing is clear about load support in CC boards. The more
you push on <BR>it, the more it resists... until its overloaded of
course. But until <BR>that point there is definitely load support and
the ribs are definitely <BR>part of that... just not in the sense of
beams.</FONT></BLOCKQUOTE>
<DIV><STRONG> This is true but the ribs are adding stiffness
& mass & mass is a often neglected piece of the
discussion at times. Ie. I've heard many C.C. board with little crown or
bearing that really sounded to my ear,very good, enjoyed them greatly. So what's
making them work? rib stiffness/ panel assembly stiffness & being glued as
an assembly to the rim adds stiffness.</STRONG></DIV>
<DIV><STRONG> When I load up a RC & partially panel
supported board, there can be a very powerful strong non-linear resistence
during the pre stress bearing set up. As I pound the board
down, slipping a wooden wedge between the central plate strut, the
resistence to further deflection stops at about 3 to 4 mm even if I continue to
pound really hard with fist on bridge. It feels like I'm pounding on a gym floor
at that point. The stiffness in that develops in a Sitka panel at 5.5 to 6.0
E.M.C. can exert a lot of stiffness factor which really quite
amazing. & So is a purelay C.C. panel at 4% as well. I got to
thinkling about how strong spruce expansion is when considering ,that a
thoroughly dried C.C. a panel can bend 1 2 or more ribs for really quite
along time and sound quite good. This is amzing. </STRONG></DIV>
<DIV><STRONG> The longevity issues & reliability
issues of C.C. boards are always the big question mark. Ie the G-2 Yamaha
I wrote about thinning the panel on is a C.C. board but with sitka spruce
ribs. Yikes How long can that board convince those stiff suckers from
sucking the life out of the crown, & it's only 29 years old. In 20
years it may be ready for the dumper, as are many mass produced
pianos.</STRONG></DIV>
<DIV><STRONG> In my boards I
know panel expansion gives some non linear strength
but I love the way they sound. I've got a pretty stiff rib set under
there as well. I'm wondering if the non linear panel qualities are
noticed or utilized more predominately in the large bottom end of the
panel. I've been considering that the shorter ribs in the treble end, Say
the last 5 ribs, are getting short enough to perhaps add beam strength as they
don't crown much Even under panel compression a flat rib doesn't normally
show much residual crown when strung up & the noticeably shorter spans the
board makes from belly rail to rim also adds a bit of stiffness but it seems to
me that it is the whole of the structure itself which is seen as a mystery as to
how to design one from an engeneering standpoint & understanding it. Hey it
works, we can't argue with that...but how well, how long....this we can debate
till were blue in de face.</STRONG></DIV>
<DIV><STRONG> Dale</STRONG></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000
size=2><BR><BR>Cheers<BR>RicB<BR><BR><BR><BR><BR><BR><BR>------------------<BR><BR>Dale,<BR>Those
ribs were originally built into a CC board. How can a<BR>compression
crowned board get mechanical support from the rib<BR>scale, however
"good" the scale looks? The ribs in CC boards<BR>resist the crown that
panel compression is trying to form and<BR>maintain, and just put more
compression load on the panel. -----Ron<BR><BR> No, I get all that
Ron, but if the ribs are built significantly taller &<BR>of stiffer
material by design then more panel compression can be taken
<BR>out of<BR>the equation. Another thought is, & I've
witnessed this quite a few times<BR>is, that Stwy A's (1 & 2"s) in
general can produce a pretty wonderful <BR>sound<BR>even with a flat
or flattish board providing there is some small but<BR>consistent
bearing load still intact so in this case it would seem that <BR>there
are<BR>enough impedance factors about the rib scale to make the system
work <BR>rather well.<BR>Ok maybe a freak of nature but it happens
fairly frequently. <BR> About 5 years back I had such an
long A I was going to resell it. It <BR>had<BR>Steinway hammers which
were quite soft & made it sound really good. <BR>It
was<BR>hard to imagine that a new board would make it sound much better.
It truly<BR>sounded glorious but it was a spec job & I don't sell
old boards very <BR>often. I<BR>didn't do any thing to the action until
later for a really good A b<BR>comparison.<BR> So I built a
board with the same number of ribs making them crowned at<BR>about 60
ft. Made em taller but not much. Used sugar pine in the bottom
&<BR>yellow pine in the top. The sound was cleaner and the
sustain was <BR>about the same<BR>which was awesome. It just had
it!!<BR> I attribute much of this to the original basic rib scale
design. <BR>Something<BR>was working or several things were. Do you see
what I'm saying?<BR> I'll crunch some numbers & see what I
got. I greatly Appreciate the<BR>design sharing & information
swap.<BR> Thanks<BR> Dale<BR><BR><BR>It's an entirely
different system. Do a bearing load analysis<BR>on the ribs as load
carrying beams and see what the numbers<BR>say. They'll say that the rib
scale isn't adequate to support<BR>bearing without substantial panel
compression support.</FONT></BLOCKQUOTE>
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