[Files] Re: B 458198, string deflections

[Overs Pianos]

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Hi Kent and all,

>Following up:
>
>My observations do not confirm the presence of significant grooving 
>on the bridge, no evidence of aggressive string seating, just some 
>scuffing as the route of the string over the bridge changed. Try 
>this view and note that the damage to the bridge is more obvious:
>
><http://tinyurl.com/dkjo2>http://tinyurl.com/dkjo2
>
><https://www.moypiano.com/ptg/files/attachments/9f/c1/94/30/dscn1194.jpg>https://www.moypiano.com/ptg/files/attachments/9f/c1/94/30/dscn1194.jpg
>
>I'm still convinced that the high angle of string off the backscale 
>side of the bridge is a source of the damage. The pins along the 
>speaking length side of the bridge do not show significant movement.

I totally agree with you Kent. Excessive string angle is almost 
certainly the primary cause of failure of this bridge. Its not only a 
poor layout but it is poorly executed. Look at the 
second-note-from-the-left pin group. You'd be hard pressed to find 
any more careless  bridge pinning anywhere. And this manufacturer 
still claims to be building world class pianos - I very much doubt 
it. Notice also that the deformation of the left-rear bridge pins (as 
viewed in the above links) appear to be exhibiting greater 
deformation than the right side unison bridge pins. The bridge pins 
are laid with a relatively close spacing of the unisons (although 
there are more severe examples of this than the bridge shown). This 
allows bridge-pin failure to sort of stack up, with the greater 
movement being in the pin which is being forced towards the other two 
bridge pins. I've noticed this before from various manufacturers who 
should have had better corporate memory, since they've on occasions 
reverted to this inferior layout after doing it better at a previous 
time.

Ron N's post which includes vector force calculations for the various 
pin angles shows why such poorly laid high-offset bridges fail more.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron@overspianos.com.au
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