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 > > > > -- > ______________________________________________________________________ > Delacour Pianos * Silo * Deverel Farm * Milborne St. Andrew > Dorset DT11 0HX * England > Phone: +44 1202 731031 > Mobile: +44 7801 310 689 * Fax: +44 870 705 3241 > ______________________________________________________________________
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