John.. Thanks for the reply. Again... I ask these things so as to get straight whats actually going on where, not so much because I am trying to show anything in particular. One question about significant forces and unsignificant forces, that unsettles me a bit. It appears that we are writting off the significance of any particular stress if the resistance to that stress is very high. Take the straight tensioning of the rib for example.... that is looked away from because it has such a high tensil strength along the grain... yet the thing is stressed with the same psi that the panel is. So ok.. the panel readily compresses, and the rib does not so readilly lengthen... but the stress level still remains the same on both. I guess I am saying... so what if the rib only lengthens by a fraction of a mm... isnt it the amount of stress on it thats important ? RicB John Hartman wrote: > Richard, > > I say these things are correct but how important are they. You have to > weed out the insignificant things such as the force needed to bend the > panel across the grain. Go to your nearest soundboard replacement shop, > "Soundboards are Us" for example and get a piece of panel spruce. Try > bending it across the grain. The forces here are insignificant. Same > with how the bearing compresses the panel vertically. True it does have > a force but it is not enough to take into account. I have never seen a > panel that was indented by the bridge. As an assignment why don't you > figure out the force in psi that the bridge pushed down on the panel? > Get back to me with some numbers. > > The two that are significant are the compression force the panel exerts > to bend the rib (in an panel crowned board) and the shear force between > the panel and the rib (due to Panel crowning and changes in EMC, not by > bending the panel) taken along the rib. > > John Hartman RPT > -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html
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