R,C&S question JD

[David Love]

Percent residual crown doesn’t tell you much in a system that has variable
radius control.  If you start with a rib that has 10 mm of crown and deflect
it 5 mm it has 50% left.  If you start with a rib with 5 mm of crown and
deflect it 5 mm it has 0%.  But they both have the same amount of deflection
for the given load.   Targeted amounts of crown in pure CC boards are
different because you are more limited to the amount of crowning you can get
by virtue of panel compression.  Like Ron, I would be interested to know
from those of you do pure CC assemblies what your stated goals are in terms
of crown and what you can realistically hope to achieve along specified rib
lengths.  My own view is that it is this unpredictability (among other
things) that is a large part of the problem with pure CC boards.

David Love
davidlovepianos at comcast.net
www.davidlovepianos.com 



  Even if a compression Crowned board could bend those short treble ribs
into a 60 ft radius it would be negligibly measurable.  SO 25 % of residual
crown of that is almost zip.  Del & others  have made the case that the
upper treble area is driven primarily by mass & stiffness due to the smaller
board area & stiff ribs... I agree.
  I crown these ribs as tight as 15 ft but even so on a 15 inch rib were
only talking scant MM or 2. But I like having something to push against that
resembles real crown.
  Makes sense?
  Dale