Richard Brekne wrote: > > Lay the panel flat after it was dried out and then blocked the tangential ends > (perpedicular to grain). When it takes on humidity it is compressesed radially .. > against the tangential face (edge). Yes ?? O.K. > But we dont actually block the tangential edges... we glue ribs onto one of the > radial faces (the underside of the panel) and thus restrict this same (radial) > expansion... so we get a somewhat predictable crown instead of random buckling (I > suppose). > > So far so good ?? O.K. > So... the panel starts to crown then... and in addition to simple radial compression > of the panel, there is some form of bending stress introduced. Then putting > downbearing into the picture... you are pushing straight down on the upper radial > face of the panel...doesnt that introduce some loading along grain the of the panel > ? I dont mean the transverse direction as the panel isnt bent this way...(or not > much anyways). I mean... you are pushing downwards at some spot close to the middle > of this big panel... on its radial face.... I guess what I am wondering is .. isnt > there some shear stress along the grain of the panel introduced by pressing directly > down on panel ? > > Perhaps a bit off the wall...:)... but I just want to make sure of things as I go > along. 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 John Hartman Pianos [link redacted at request of site owner - Jul 25, 2015] Rebuilding Steinway and Mason & Hamlin Grand Pianos Since 1979 Piano Technicians Journal Journal Illustrator/Contributing Editor [link redacted at request of site owner - Jul 25, 2015]
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