No downbearing ?

[Isaac sur Noos]

My understanding is that crowned ribs where used on most brands at the
beginning of the last century, so called compression crowning being a
relatively modern method (no rea date but been said the 60's)

All old Erard and Pleyel that have crown and even lots of apparent
downbearing (like the 18587 Erard I just worked on) where of course
then rib crowned.

Where the soundboard glued in curved beds then, most probably assuming
the ribs shape.

Greetings

Isaac OLEG.


 -----Message d'origine-----
De : pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]De la
part de Delwin D Fandrich
Envoyé : samedi 3 janvier 2004 21:25
À : Pianotech
Objet : Re: No downbearing ?



----- Original Message -----
From: Erwinspiano@aol.com
To: pianotech@ptg.org
Sent: January 02, 2004 2:20 PM
Subject: Re: No downbearing ?


In a message dated 1/2/2004 11:51:20 AM Pacific Standard Time,
pianobuilders@olynet.com writes:
    I wonder if it was common practice to press boards on a flat deck
which is what I've always heard.(I forget where) Perhaps no one really
knows but even if they were pressed in a dished caul with ribs that
long & usually not very tall how much crown could the panel really
retain over time. I recently saw  1920 ish Knabe upright with very
tall ribs & enough of them. I didn't check the crown at that time but
I will when next I see it. This piano was very well preserved ,great
sound. Thanks for the replies.
   Dale

>From what little I've been able to piece together in talking with some
old bellymen both were common. The dished caul was introduced along
with the crowned rib but was often used with flat ribs in the
misunderstood hope that this would somehow reduce the stress on the
panel.

In general relatively low, wide ribs are used with compression-crowned
soundboard systems (they must be flexible enough for the expanding
panel to force a crown) and taller ribs are used with rib-crowned
systems (they must be stiff enough to support crown). At the risk of
stirring up once again The Great Soundboard Debates of 2003, ribs do
not support crown in a compression-crowned system. They must be
relatively flexible. The last Knabe upright I was involved with had
crowned ribs.

Del