Laminated ribs.

[Delwin D Fandrich]

----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: May 08, 2003 1:30 PM
Subject: Re: Laminated ribs.


>
> Hmmm... doesnt that make them rather.... springy in comparison to
> machine crowning solid wood ? And what about compression issues, creep
> etc relative to solid wood ? I remember seeing a demonstration once
> about a kind of rocking chair made by pressing lamininants into a curve.
> As long as you whatever stress applied increased the curvature of the
> finished lamininats they were very strong, but if you applied stress in
> the opposite direction the things split apart like 10 year dried
> firewood.


Except for the laminated ribs being somewhat more consistent I've not
noticed much of any difference in their strength or stiffness
characteristic. Why should they be? They are made of the same wood.

What about compression issues? Why should there be any more compression
stress on the wood fibers in a laminated rib than there are in a solid rib?
We've tried stressing the things every which way and have found invariably
the solid wood rib cracks or breaks before the laminate does.

About the rocking chair, what can I say? Soundboard ribs and rocking chairs
are rather different in their construction and the stresses involved. For
one, the curve radius in a laminated rib is quite shallow. Unless the wood
had to be heated or steamed in the process of making the laminate, and
unless the bending radius is rather extreme the strength of the laminate
should be equal to a similar solid wood member. Laminates have been used in
everything from automobile bridge members to church beams to piano rims. If
I were making the rocking chair in question I'd want to know why the thing
was breaking.

Del