[pianotech] new board evaluation

[David Love]

I'm curious to know more about why the rim needed to be built up.  Why do
you that part of the board wouldn't go down very well?  

Though I realize that the core wire dimensions of .061 are the original,
they are way too thick.   

With most boards on this piano being closer to 8mm with thinning around the
perimeter it does sound like this is a combination of a too stiff panel in
the bass plus a short backscale plus a too stiff core wire.  All those in
combination will tend to produce what you describe.

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Gene Nelson
Sent: Sunday, December 07, 2008 3:52 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] new board evaluation



 What's the back scale length of A-0?
 95mm

 Not an awful lot. Is that all the room there was?
>>>>No but I was advised to have 90 mm as a minimum. Probably a bit gun shy.

 Bass rescaled?
Only slightly - reduced spl to get slightly longer tail lengths.

 What was the original A-0 back scale?
>>>>I believe it was 70mm

 What's the core diameter of A-0?
 .058

 Still fairly stout.
>>>My mistake on the core wire it is really .061" - sorry about the 
>>>misinformation.
 I'd say it's likely a combination the
 board being too stiff, with the back length, and core diameter
 contributing. Up to about 6-1/2' (200cm) I float the tail
 around the low bass too. The bridge is for sure clearing the
 edge of the plate, right?
>>>>Yes, double checked and positively clears the plate.

I recently had an embarrassing
 reminder of how easily that can happen.


 What "design" board did you build?
>> Radius cut ribs - 60 ft in the bass and tapering to the treble - 16 
>> total. Made from quartered Sitka. Glue up at around 6 to 6.5 mc.
>
 What method did you use to determine the count and
 dimensioning of the ribs?

>>>>I calculated the downbearing force of the strings at every unison based 
>>>>on what I thought the bearing would be in the end when loaded. Spaced 
>>>>the ribs to support this and started with the end of bridges and then 
>>>>the calculated # of unisons with fudging as needed to clear nose bolts.
Kept the ribs taller than wide and spaced them on the unisons so that a 
known load was applied to each rib.
Designed rib hight and width so that calculated deflection and max load 
capacity looked good. Deflection ranged from .250" in the lo bass, .450" at 
rib #7 and .036" at the top treble. Also considered available crown based on

radius and how much of it I wanted to use for bearing.
The load carrying capacity of the ribs ranged from 27 lbs in the lo bass, 52

lbs at rib #7 and 90 lbs at the top treble.


 The board was not cut off in the bass but the inner rim gluing surface
 was built up with epoxy and veneer to accomidate the part of the board
 that did not want to go down on the rim without a struggle.

 Why not, and why?

>>>>Customer would not be happy. The build up I thought was the next best 
>>>>thing.

Board thickness is 9mm - on the fat side - no diaphraming.
Again, why

>>>>No good answer for that one.
One thought along this line that I did have was my experience when I visited

David Rubenstein's 12' piano. It has a 1/2" thick board and the tone is very

dark with tremendous power - I really liked it. This probably influenced me 
somewhat.

Gene
>