Grand Rim Construction

[Delwin D Fandrich]

----- 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