[CAUT] question

[David Love]

The reasoning is probably less important than the result.  If you are using
the riblets it's because there's already a problem and the theory about
what's happening with what is out the window anyway.  

 

David Love

www.davidlovepianos.com

 

From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Richard Brekne
Sent: Thursday, April 02, 2009 3:13 PM
To: caut at ptg.org
Subject: Re: [CAUT] question

 

Hi folks


"The riblets just add some extra stiffness to the overall assembly--or the
section where they are installed.  The design of them is such that the
center of the riblet needs to be pulled up by the screw to contact the board
in the center.  That insures that the outer feet also make contact."

This is the other bit that bothers me about these. As the things are to be
screwed into the bottom area around the bridge, the net effect of  forcing
the middle of the riblet upwards is to engage a reverse crown  force (over a
very short breadth) on the underside of the panel. I understand the idea is
that one <<bends>> the riblet by screwing it in.... but in doing so one has
to remember the reasoning used time and time again here as one of the main
objections some have to CC boards in general... the ribs resist bending. In
essence then one is exerting a downward force on the area of the panel that
the screw goes in and pushing up on the feet. Even tho this pressure is
slight... its there and the idea doesn't appeal to me.

As far as gluing any part of the riblet to the soundboard at all is
concerned... it still strikes me that any along the grain length of rib
however short that is glued cross grain to the soundboard will exert (on the
glued breadth of the soundboard/riblet contact) the same kind of stresses
that any length of rib will.  As such, a short segment glued cross grain at
high RH seems like a recipe for SB tension cracks later on at the area of
the glue joint.  I dont see how you can get around this myself. 

Cheers
RicB

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