Compression Question

[Bill Ballard]

At 12:14 PM -0400 8/28/03, John Hartman wrote:
>BTW you can use some of the same formulas to find the change in EMC 
>that will start to cause compression set if the wood is confined. 
>For quarter sawn spruce I get 6.5%.  Using the figure you can come 
>up with a range of relative humidity that a soundboard can safely 
>live in. If you rib your board at 4.5% the safe range is 20% to 60% 
>disregarding the compression due to ribbing and down bearing. If you 
>rib your board at 6.5% the range is from 30% to 70% RH.
>
>I would say you need to narrow theses figures about 10% due to other 
>stresses on the board. I consider the safe range is from 30% to 60% 
>RH for a board ribbed at 6.5% EMC.

Thanks, John. You've got me started on my own homework assignment. 
When you say, "narrow these figures about 10%", it seems you mean 60% 
RH - 10% RH, instead of 60% * .9. I need to adjust the figure for a 
board ribbed @ 4.5%, on the assumption that was the operating EMC (as 
Del would assume).

Regardless of the thread earlier this Spring about the difficulty of 
determining the original manner of board assembly 50-100 years later, 
I'd assume that if it's still showing crown AND the bottom side of 
the rib is flat, the ribs were originally curved. That doesn't rule 
out the possibility that Petroff both crowns their ribs AND assembles 
the board at killer low EMC.

That EMC will determine what the ceiling for ambient RH the piano 
owner must enforce. Regardless, the piano is now dependent on climate 
control to stave off premature splitting. Ironic, considering the 
dealer's attitude towards D-Cs (he hadn't heard of the Smart Bars) 
and the regional rep (he stated that Steinway discouraged their use), 
and Petroff's official position on climate control and D-Cs.

At 11:02 PM -0400 8/28/03, Erwinspiano@aol.com wrote:
>I've used the same spruce panels as Petrof  and found it to be a 
>very brittle wood. Or at least it was the spruce Geneva 
>international sold as Petrof European stock. Of all the spruces I've 
>worked with I least liked this variety. It would split and crack 
>along the glue joints with out much encouragement. Or elsewhere.
>     Obviously the panels are being dried to much for many parts of 
>the USA (all Parts) The dealer needs to get his head out of the sand 
>as to the damp-chaser isssue. I mean get real Dude.

I'm not sure I'd use you experience in my first conversation with 
Petroff, maybe my 3d or 4th. But it's valuable as background.

Thanks to all,

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

"Out here on the food chain, you either          
    diet,die, or dine"
     ...........folksinger Mark Graham
+++++++++++++++++++++