<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html>   Erwinspiano@aol.com wrote: <blockquote TYPE=CITE>       Calin       As I'm sure you know the board your describing to be made with flat ribs will not stay straight but crown once the dried panel gains moisture. What you're describing is the old syle  pure compression type of board making. That is unless you mean that  no panel drying is done prior to the rib glue up. In this hypothetical case some amount of bearing is no doubt likely to reverse the crown of the board don't you think. And the panel will likely crack as soon as it dips below it's realitively high E.M.C at the time of ribbing. Of course if the ribs were made deep enough like a very thick beam I suppose you could achieve the stiffness as you suggest but is this really your question?    Regards---Dale    </blockquote> Good points here from Dale, and interesting also in that they illustrate one reason why compression to some degree is desirable... for not to say essential. The ribs restrict the panels tendancy to react to climatic changes. Building a panel assembly such that rib constriction that could occur when the climate is dry, is ruled out by the compression built into the whole thing.   >Calin writes: >A rib-crowned board, if I understand things right, should be not that much different in terms of stiffness from a flat board with flat >ribs that avethe same strength. >A crowned rib is not working like an arch in architecture - it works like a beam supporting a vertical load, at least that seems to >be what people say around here. So wether you make it crowned or not, this should be relatively unimportant. Interesting comment, and I will enjoy the answers you get. One will most certainly be that increase stiffness that can be created by strings pressing down on the board will be absent in the flat panel. You could use something other then wood for the panel to achieve this design. Cheers -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A> <A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>  </html>