Hygrometer

[Ron Nossaman]

>Ron,
>         If I correctly understand what you are doing with your 
> sophisticated :-) setup, you are looking for a change not necessarily a 
> specific number from your meter. Correct?

Nope. The T & RH will give me an MC. I just have to hold the T&RH long 
enough for the wood to reach the target MC. Patience, patience.


>Do you feel that you can adequately state the moisture content of the wood 
>from an instrument designed to measure the air simply because it is 
>against the wood and trapped under a blanket?

Pretty close. At least close enough for building soundboards.


>What would happen to the measurements if you introduced , say, a 6" air 
>pocket around the hygrometer instead of having the blanket on top of the 
>meter? Do you think that the readings would be different?

Shouldn't make any real difference. The idea is to soak the wood in a 
controlled T&RH until the MC stabilizes. the blanket is just to contain the 
heat, while passing the moisture, to get the RH where I want it. Then it's 
a matter of the wood catching up.


>the environment you create with the space heater under the piano is not 
>necessarily the same environment above the board . Would you agree? If you 
>measured the MC under and over the board they would surely be different, right?

Right. That's why I put the hygrometer on top of the board. If I get the 
results I want there, I can assume the rest of the board has already been 
there.


>  Could it be possible that some degree of instability is possible because 
> of this? I know the board is relatively thin but without air circulating 
> around the top could there be potential problems with uneven rates of 
> contraction of wood fibers? Would this cause future problems with cracks 
> or is this all semantics and nothing to worry about. Thanks for your 
> indulgence of my random thoughts!
>
>Greg


I don't think so. There will surely be a difference, but how truly critical 
is it in practice? A very big deal is almost universally made about not 
subjecting a soundboard panel to any undue stress - real or imagined - 
often while subjecting it to a compression level exceeding the fiber stress 
proportional limit of the material in trying to form and maintain a 
compression crown against the resistance of the ribs and string bearing. 
Duh! In practice, the creep rate and general plasticity of spruce  means 
that the stuff will accommodate most any minor top to bottom stress 
differential uneven drying could possibly put on it, without it even 
noticing - any more than you will. This stuff adapts wonderfully, and if 
you don't ask more of it from a structural load design standpoint than it's 
capable of giving, it will cheerfully meet you half way.

Again, the magic is in the design, not in the details of the process.

But that's just my opinion. <G>

Incidentally, I'm a lifelong fan of random thoughts, as opposed to no thoughts.

Ron N