RC vs CC again

[Farrell]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment
I don't deny for a moment that I may be missing the ball here entirely - =
I'm really just trying to kick this around, I think much like yourself. =
That being said ......

When you have a CC soundboard with no load on it, the rib is stressed in =
that it is trying to straighten out at all times. The panel is =
compressed - that is what makes the rib bend, panel compression. When a =
load is applied to the top of the soundboard downward, the panel =
compresses more and the rib is returned to a state closer to straight =
and thus lessens stress on the rib.

I don't understand the logic of "...the underside of the panel will want =
to expand when down bearing is applied...". What leads you to that =
conclusion? Why would the underside of the panel want to expand? The =
entire thickness of the panel would compress I should think.

Maybe I'm all wet here, but that's what makes sense to me. Anyone else =
care to chime in?

Terry Farrell
  ----- Original Message -----=20
  From: Richard Brekne=20
  To: Pianotech=20
  Sent: Monday, October 06, 2003 5:40 PM
  Subject: Re: RC vs CC again


   =20
  Farrell wrote:=20

     Comments below - I need some clarification to address these issues.

  Rather then copy over all this let me just re-word and see if that =
helps.=20

  A crowned CC panel, in addition to whatever else it is... is a curved =
peice of wood. And as such the convex side will be stretched relative to =
the concave side.  The overall levels of compression in the panel make =
no difference in this regard. When downbearing is applied, then the =
convex side will be compressed, and the concave side will stretch =
relative to their condition before downbearing is applied. . But the =
ribs resist this stretching tendancy, they will resist any stretching =
tendancy on the part of the underside of the soundboard.=20

  In otherwords... the underside of the panel tried to expand when it =
took on humidity... the ribs resisted this and crown was induced and the =
ribs were bent. Pushing down on the board will increase the panels =
pressure on the ribs because the underside wants to expand even more.=20
   =20

    So as stated above, when you apply downbearing, yes, the concave =
side of the rib stretches, but only with reference to its curved =
compressed state - it doesn't stretch relative to when it was straight. =
I think it is more appropriate and more clear to state that when =
downbearing is applied, the concave side of the rib experiences a =
reduction of its compressed state.
  Terry.. I think you misread something here out of what I was saying =
...yes ??  Applying downbearing will stretch the concave side of the =
panel.. the convex side of the rib will see this tendancy to expand just =
as it sees any tendancy to expand on the part of the panels =
underside.... it will resist the expansion. Hence the rib will =
experience an increase in stress,... ergo it has to be supporting the =
crown against downbearing.  Just because the the rib is a bit flatter, =
and there is an apparent lessening of the compression in the lower half =
of the rib,  doesnt mean we can ignore this increase in stress on the =
rib as a whole... or what ?=20
  I dont see at this point how we can get around that, except by =
refuting that the underside of the panel will want to expand when down =
bearing is applied... and I dont see how we can get there at all.=20

  I hope I've made clear where I'm getting hung up accepting this "ribs =
dont support crown against downbearing" position.=20

  Cheers=20
  RicB=20

  --=20
  Richard Brekne=20
  RPT, N.P.T.F.=20
  UiB, Bergen, Norway=20
  mailto:rbrekne@broadpark.no=20
  http://home.broadpark.no/~rbrekne/ricmain.html=20
  http://www.hf.uib.no/grieg/personer/cv_RB.html=20
   =20

---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/a9/f4/7d/97/attachment.htm

---------------------- multipart/alternative attachment--