Compression Question

[Richard Brekne]

I see you are two steps ahead of me in one direction here Ron. And of course I
agree that I have seen this in pianos, and thats half of why I asked. The other
half is that I'm still trying to get ahold of exactly how this shrinking and
expanding works.... especially in the face of a compressioned peice of wood.
Something about the fact that a panel having assumed a certain set of
dimensions at a given EMC tells me that it shouldnt be able to get smaller then
those same dimensions at that same EMC.

Ok... so compressing the panel as described doesnt stop a panel from shrinking
as its moisture content drops... tho it does to some degree inhibit that
shrinking capacity. I suppose this means that the cells would be even tighter
pulled together as origionally they were when first dried out to the same EMC.
I guess its this last that causes my present head scratching.

RicB


Ron Nossaman wrote:

> >If you take an unribbed panel, and dry it out to the extremes of 4% MC,
> >and then constrain its dimensions at that so that it is not allowed to
> >expand either outwards, or upwards or in any fashion and bring the MC up
> >to 13 % the panel will get pretty severely compressed... yes ?... ok..
> >If you allow this to sit over enough time that if in releasing the
> >constraints the panel simply retains the dimensions it had under
> >constrainment.... then what happens to the size of this panel  if you
> >dry it down to 4 % again ?
>
> You've seen the answer to this question in a lot of pianos. It will shrink,
> but not nearly as much as an un-crushed panel would. If the panel didn't
> still shrink after being crushed and damaged by restraint under expansion,
> it wouldn't ever crack.
>
> Ron N
>
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html