Grand Rim Construction

[Delwin D Fandrich]

----- Original Message -----
From: Paul <tunenbww@clear.lakes.com>
To: <pianotech@ptg.org>
Sent: May 03, 2000 5:55 AM
Subject: Re: Grand Rim Construction


> Brian
> You may get several replies on this. Here's my take on it :  instead of
the
> rim being bent with several layers of wood, saw cut are made almost
through
> at a right angle to the length of the rim piece. By the spacing and the
> depth of these cuts, the rim piece becomes flexible so it can be formed
> around a mold with very little stress. If I remember correctly, Bosey
glues
> this rim piece directly to the inner rim. After it is dried. they install
a
> face veneer to the inside of the rim piece to cover the saw cuts, fill the
> ends of the saw cuts with wedges and add an edge banding to hide all the
> joints. A lot of putzing to get a rim. They claim it is stress free and
adds
> to the singing tone of the piano.
>
> Paul Chick
--------------------------------------------------

Your description of the Bosendorfer rim is correct.  The cuts are spaced
fairly close together where the rim curve is of smaller radius (a tighter
bend) and further apart where the bend is more gentle.  This is a
time-honored process used in the furniture making industry to make various
curved pieces.  It has been largely replaced in furniture manufacturing by
the bent lamination process because the latter is stronger, more stable and
easier to accomplish in production.  Still, for a one-off bent piece for a
bow front chest or whatever, it is fast and fairly easy to do in the small
shop.

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.

Del