Bridge Crown

[David Love]

Nice photos.  One obvious question is that even though the bridge was
creating a portion of the crown on the detached panel, how much crown would
it actually support under tension.  From previous posts on this topic the
answer seems to be virtually none.  So if the crowned bridge was part of
the design to support crown under tension, it would appear that it would
have been for naught.  What do you think?

David Love
davidlovepianos@earthlink.net


> [Original Message]
[link redacted at request of site owner - Jul 25, 2015]
> To: Pianotech <pianotech@ptg.org>
> Date: 12/1/2003 5:46:15 PM
> Subject: Bridge Crown
>
> This topic comes up from time to time and my take on it is that on the 
> Steinway and Mason & Hamlins the bridges are machined with a definite 
> crown. This crown helps to support bearing just as crowning the ribs 
> does. How much benefit this has on the performance of the pianos I don't 
> know but it seems a logical step toward creating a high quality
soundboard.
>
> Until now I have not had the opportunity to show how this works. I have 
> in the shop at the moment a Steinway L built in 1960. While not in 
> perfect condition there is enough of the original crown, both along the 
> ribs and along the bridges to see what the builder had in mind.
>
[link redacted at request of site owner - Jul 25, 2015]
>
> Shows the soundboard removed from the case (about 3 inches are removed 
> along the spine and bent side from my removing process). The crown along 
> the bridge is clearly visible.
>
[link redacted at request of site owner - Jul 25, 2015]
>
> Shows the soundboard after removing the bridges. This clearly shows that 
> the bridges were creating the crown from front to back along the grain.
>
[link redacted at request of site owner - Jul 25, 2015]
>
> Shows the bass bridge, there is about 2mm of crown.
>
> In addition I have two photos showing what remains of the rib crown.
>
[link redacted at request of site owner - Jul 25, 2015]
[link redacted at request of site owner - Jul 25, 2015]
>
> This is about 2/3rds to 1/2 of what I would consider optimum rib crown 
> for this pianos. So at least in this case a panel crowned soundboard has 
> survived a few years after leaving the factory.
> -- 
> 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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