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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