Manually pre-compressing a panel... was Soundboard drydown forinstallation

[Farrell]

> Since the inevitable compression set of the soundboard panel will come 
> sooner or later...

Why is compression set inevitable? I believe it is on most any compression 
crowned soundboard. But if you build a rib crowned and supported soundboard 
assembly and don't expose the piano to extremes of humidity, the panel will 
not want to shrink or swell much and as such, should never experience 
compression set.

> and since compressed wood is somewhat stiffer then uncompressed wood in 
> the direction of compression...

Ummm, I guess it probably is (I'm not an expert with that and I don't 
compress my panels much at all). But whereas compressed wood might be 
stiffer than uncompressed wood, compression-damaged or compression-set wood 
shouldn't be any stiffer than uncompressed wood.

> why hasn't anyone tried pre-compressing a panel so as to push it way past 
> its compression limits... essentially taking future compression set out of 
> the picture entirely... and then build a RC&S assembly with the thing ?

Well, maybe because it is easier to work with spruce lumber rather than 
spruce pulp? And besides, if you crush the wood, you will then have more 
wood in less volume - a lower strength to weight ratio (not to mention how 
crushing the wood would likely have negative effects on the wood strength). 
The reason I build soundboards from Sitka Spruce lumber is that it is the 
highest strength to weight ratio wood. Or maybe I don't understand where you 
are going with your statement.

Terry Farrell

----- Original Message -----
>    Perhaps unrelated, but none-the-less interesting and perhaps unknown to
>    many, is how much and how easily one can reduce the cross-grain
>    dimension of
>    a thin spruce panel when clamping. I've never measured it, but I would
>    estimate that one could reduce the width of a meter-wide panel by 5
>    to 10 mm
>    with only finger torquing on a few clamps. Spruce is very spongy
>    that way.
>
> This is another point that bugs me.  Since the inevitable compression set 
> of the soundboard panel will come sooner or later... and since compressed 
> wood is somewhat stiffer then uncompressed wood in the direction of 
> compression... why hasn't anyone tried pre-compressing a panel so as to 
> push it way past its compression limits... essentially taking future 
> compression set out of the picture entirely... and then build a RC&S 
> assembly with the thing ?
>
> I'm sure there is a very good reason why not to... but I haven't a clue as 
> to what it would be.
> Cheers
> RicB
>