Restoring crown (was RC Vs CC again)

[Alan Forsyth]

> Del wrote;
>
> >>"do you suppose it somehow -- miraculously -- lost
> its desire to get itself straightened out?">>
>
> As an offshoot to this topic, what then happens to the wood fibres in a
hammershank when we cast them with a heat source? They certainly have lost
their "memory" in this case. Would "time" under stress be a factor in a rib
losing it's "memory"?
>
> Just asking!
> Alan Forsyth


	 >>>Ah, now we introduce an outside influence.

	Yes, applied heat does soften the lignin (basically a chemically 	complex,
thermalsetting adhesive) and allows some permanent 	reorientation of the
wood fibers. We do not typically heat ribs 	sufficiently to either give them
crown or to remove crown once 	it is established however.

	And yes, time under load is a factor. It is one of the reasons a 	piece of
wood under continual stress changes shape over time. 	But, while 	this is a
factor in why a compression-crowned 	soundboard assembly (and, though to a
much lesser extent, a rib 	crowned soundboard assembly as well) will lose
crown over a 	period of years, it is not germane to the current discussion.

	Del  >>>

Hi Del, thanks for your post. When you say "We do not typically heat ribs
sufficiently to either give them crown or to remove crown once it is
established however." does this mean that, say in an old banger situation,
one could theoretically restore crown by heat setting the ribs instead of
going through the uneconomic procedure of re-building a soundboard?

I once thought of steaming a soundboard in an old banger back into shape to
try and get some oomph back into it, but then realized that the glue joints
would probably fail. One day I will try it just for fun when I'm
...er...board!

Regards
Alan Forsyth