String vibrations (was Re: Stuart)

[Overs Pianos]

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>At 7:23 AM -0400 24/9/03, Farrell wrote:
>
>Is anyone aware of the shape of these agraffes where the string contacts the
>agraffe?

The early Stuart agraffes had small-radius ceramic inserts on the 
speaking length side, which I considered to be somewhat of an 
overkill. The recent versions have a steel pin, but I don't know if 
they are hardened or in an annealed condition.

At 10:59 AM -0400 23/9/03, Erwinspiano@aol.com wrote:
>        Hi  Ron O
>    I have a (1950s I think) 6ft Sohmer I posted about earlier that 
>has brass bridge aggraffes in the tenor  and first capo section but 
>not in the bass.  Since Phil Ford was in the shop the other day we 
>looked at the bottom of it and it has a what looks like a 1/4" maple 
>piece running under the bridge on the bottom of the board. He said 
>it might be there to keep the bridge from rolling backwards because 
>of the way the pressures are applied to the bridge.

It may have been of sufficient dimensions so as to enhance the 
rigidity of the bridge system. How high was nominal height of the 
Sohmer bridge wood, and what were the sectional sizes of the 1/4" 
maple under the panel?

>    In this config. the strings come thru the agraffe and then up 
>over a sligthly rounded hump then on to the hitch.

In this configuration at least it would reduce the tendency of the 
agraffe's vector forces to pull the bridge off the panel. The early 
Stuart agraffes had only one string deflection also, but they ran the 
opposite way. In the latest design the deflection is similar to the 
agraffe image Ron N. posted earlier today. That was a very neat and 
cheap-to-build design uncle Ron, since it could be manufactured in 
two press strokes only.

>  This piano has a reverse crown board as well & sings like a 
>soprano. In a previous Sohmer (also with reverse crown) I rebuilt 
>,the aggraffes screwed into the bridge with very fine machine 
>threads.  Can you imagine how time consumning that was. Well at 
>least possible if they was turned into the bridge with a drill etc. 
>My point is they were still solid in the bridge and worked well 
>after 70 yrs.
>     Why wouldn't this system be a candidate for some one like you?

May be it would, but I really haven't gotten around to addressing a 
bridge agraffe design yet, since I am still grappling with our new 
sound board design (the first version is going into piano no. 4 - 
should be glued into the case in the next few days). Just today I 
finalised the rib feathering after clamping the board into the case a 
couple of times and being dissatisfied with the deflection of the 
board under test loads. Fortunately, I chose initially to make the 
feathering shorter, paring it gradually longer until I was satisfied 
(for now) with the panel deflection.

I'm looking forward doing something about conventional bridge pins 
and falseness, which is endemic.

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