----- Original Message ----- From: Stephen Birkett <birketts@wright.aps.uoguelph.ca> To: <pianotech@ptg.org> Sent: May 16, 2000 9:03 PM Subject: Re: Grand Rim Construction > Del wrote, > > No process used to create bent furniture components is really stress-free. > > But they are correct that this type of rim construction does result in less > > stress than do others. At least initially. I'm not sure this is an > > important issue in piano construction, however. The stresses imposed on the > > veneers used to make a bent laminate rim are basically dissipated after the > > rim is a few months old. I have encountered several piano rims in which the > > original hide glue had almost completely failed and the rims had almost > > fully delaminated but which had still retained their original as-pressed > > shape. > > > Depends. Cold pressed (no steam - no heat) rims do not dissipate the > stresses - ever. I've seen a 300 year old old haprsichord bentside that, > when removed, popped back to almost flat after a spell. Heat and (or) > steam (partially) removes the stresses by plasticizing then > re-assmenbling the cellular structure of the wood polymer. Not cold > pressing, i.e. just bending the rim and forcing it bent until the glue > dries. > > Stephen ------------------------------- Interesting. For a project a few years back I dry-pressed some rims -- i.e., normal veneer lay-up, no glue -- and studied the results after varying periods of time. (Don't ask why.) After the veneer lay-up had been in the press for a week or so, the veneers had taken on a very definite set. They certainly didn't "pop...back to almost flat after a spell." I would assume that with the liberal application of water (from the adhesive) the veneers would take on even more of a set. If I ever have occasion to do something like this again, I'll do it at least once with wet veneers just to see what happens. I should also point out that most piano companies do heat their rims at some point during the process. Either by RF energy during the press operation or, as is the case with Baldwin, subsequent to pressing. Rims are allowed to stabilize in a room heated to approximately 120º F for 30 days or so. Del
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