Rib Tapering

[Richard Brekne]

Thanks  for the comments Terry.
A couple answers to your questions below. Seems like perhaps I should be 
thinking about gradual tapering here from the sound of your post.

Cheers
RicB

Farrell wrote:

> Hey Richard,
>  
> I'll stick my neck out - not that I am any authority at all on this 
> subject - but perhaps it will stir something up. I figure if I say 
> something outrageous enough, then someone that knows what they are 
> talking about will chime in.
>  
> On a compression crowned soundboard, like a Steinway, the rib acts as 
> something to keep the one side of the panel from expanding when the 
> panel takes on moisture upon removal from the hot box - that is what 
> makes the panel crown. The ribs will be of constant thickness so that 
> the soundboard develops crown evenly. The ribs are thinned only at the 
> end to keep the soundboard flexible at the perimeter.
>  
> A rib crowned soundboard will have ribs that are more evenly tapered 
> over most of their length, such as the taper you describe. That is 
> because such a shape better supports a load when applied to the middle 
> of the rib, such as downbearing on the bridge. That is what I think, 
> but you'd really need input from an engineer type to say more about 
> that subject.
>  
> Now all other manufacturers use the Steinway-shaped rib because that 
> is what Steinway does.
>  
> Is your soundboard crowned? Compression crowned? Rib crowned?

Ribs are at a mild crown... close as my rough work could get to a 90 
foot radius. They were glued on after the panel had been in 27-28 % RH 
for 3 weeks... so whether what degree of Compression that will create as 
it takes on summer humidity will qualify this as a compression crowned 
board or not I dont know. My plan was to have mild rib crown support, 
combined with mild compression crown tenancies. It is, after all, a 
small square grand and has a very light scale.

>  
> Terry Farrell
>