Compression Question

[Bill Ballard]

At 1:27 PM +0200 8/28/03, Richard Brekne 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 ?

I look forward to this answer, but at the same time would also like 
the guidelines the question is based on confirmed. I heard somewhere, 
maybe on this list, maybe in a convention classroom, that there was 
at most a 6% EMC range (from belly-room dry to living-room full 
summer humidity), through which a soundboard panel glued into a piano 
rim could go before serious compression ridge damage occurred. IOW, 
the board in Ric's example should be allowed to rise to no greater 
than 10% EMC.

Correct me. I have a customer with a 2-year-old Petroff grand, which 
at one year had serious compressions ridges, a separation between 
board and ribs, and a crack (closed during summer humidity) at the 
location of the separation. Both the dealer and the company regional 
rep downplayed the effectiveness of the Dampp-Chaser system, which 
the owner had in the Yamaha vertical traded in for the grand.

Bill Ballard RPT
NH Chapter, P.T.G.

Visit Bhod Ankur, the underwater monument to yesterday's civilisation.
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