Soundboard installation, next topic : the glue

[mccleskey112 at bellsouth.net]

Thanks John, I needed that.
Gerald mcCleskey RPT
Shreveport, LA

----- Original Message ----- 
From: "John Delacour" <JD at Pianomaker.co.uk>
To: "Pianotech List" <pianotech at ptg.org>
Sent: Wednesday, January 23, 2008 3:56 PM
Subject: Re: Soundboard installation, next topic : the glue


> At 14:20 -0600 23/1/08, Ron Nossaman wrote:
>
>>The definitions as used for the last five years or so on list are:
>
> Thank you for the concise explanation.  I know that the terms have been 
> commonly used on the list but that doesn't mean it's easy to find any 
> place in the archives where they are clearly explained and compared.
>
>>CC=compression crowned, consisting of flat ribs with panel compression 
>>forming and supporting crown under both string downbearing and the ribs' 
>>attempt to naturally straighten back out. Steinway US, Steingraeber, and 
>>Sauter build boards this way.
>
> And yet Hartwig of Steinway Hamburg is reported to say "and yes the ribs 
> are slightly curved prior to gluing them onto the board." Depending on 
> what he means by "slightly", surely that could mean a Steinway board is 
> more or less "rib-crowned" by your terminology?
>
>>RC=rib crowned, consisting of ribs with a crown machined directly into 
>>them,..
>
> Would that be the same,in effect, as saying planed to a convex curve on 
> the upper side?
>
>>..and supplying positive beam support to crown under downbearing in 
>>addition to the support supplied by panel compression.
>
> This compression being created by the force produced by the summer growth 
> (mainly) of the spruce trying to expand after being glued to the ribs in a 
> more or less dehydrated condition.  Is that what you're saying?  It seems 
> to be, but anyone reading your description without much knowledge might 
> easily ask "what compression?!"
>
>>  This is the most common construction method among today's manufacturers.
>
> And has been a common construction method for well over 120 years, is that 
> not so?
>
>>RC&S=rib crowned and supported, consisting of ribs with a crown machined 
>>directly into them, sized and numbered sufficiently to support crown under 
>>downbearing load without the aid of panel compression. To my knowledge, 
>>Walter is the only manufacturer building boards this way, though there are 
>>a number of small shops doing this now, with considerable success.
>
> Do you count yourself among that number?  If I understand this correctly 
> in the context of the other two methods and by contrast with them, then 
> when the board is glued to the ribs, presumably without any previous 
> special dehydration, the curvature resulting in the board will lead to 
> some tension in the board and when the piano is strung and the curvature 
> of the board diminishes this tension will diminish and leave the board in 
> roughly a state unstressed either by tension or by compression.  Is that, 
> broadly speaking, the intention?
>
>>And no, 15' isn't an excessively tight radius for a machine crowned rib. I 
>>go down to 4 meter in the treble
>
> That's another matter.  15 ft. was not mentioned as the radius of a 
> crowned rib but as the radius of the installed board in my picture
>
>>Whatever Wolfenden has to say about it.
>
> He has not much to say about it.
>
> JD
>
>
>
> -- 
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