Hygrometer

[Erwinspiano@AOL.COM]

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In a message dated 8/30/2002 4:38:21 PM Pacific Daylight Time, 
gnewell@ameritech.net writes:


> Subj:Re: Hygrometer 
> Date:8/30/2002 4:38:21 PM Pacific Daylight Time
> From:<A HREF="mailto:gnewell@ameritech.net">gnewell@ameritech.net</A>
> Reply-to:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
> To:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
> Sent from the Internet 
> 
>              Greg 

                    I know this question wasn't directed at me but let me 
share an answer with you.
               In my setup I have a hot box I can store a few panels in. On 
the door is a window and behind it is the radio shack temp and R.H gauge. In 
side is a series of damp chasers and a small fan on the floor. On the outside 
of the door I have a chart the tracks E.M.C. in relationship to R.H. ie   90 
degrees f. nets  5% emc in spruce. This is a chart out of I believe the 
governments wood book
   Any way if I want to be sure the board is suffienctly dry in modestly 
humid weather I let it cook for three  days unless its been sitting in the 
shop at 30% or less anyway. The fan circulating helps of course to enenly dry 
all areas of the panel.
     The same result will happen under a blanket with a space heater too. 
Nothing wrong with the way Ron does it and his other point about the rib set 
being the most critical factor should be pondered as much as this current 
question on emc.
     If your shop is humid without controls you'll want to rib the panel in 
hour or so and don't answer the phone. If Rh is lower in the shop that's 
different. My feeling is it takes a couple hours for the spruce to take on 
insuffiecnt moisture to significantly change the outcome of your rib crowned 
project. 
     Remember the conditions which many soundboard were pressed up in the 
Piano factories on the East coast were archaic at best. The zero EMC in the 
winter and 80% with high temps in the summer. In your worst day in your shop 
you'll all do better than that.
   It sounds like there is a search for parameters in this discussion which 
is important and when found will keep us from having undue  anxiety in the 
board making process.
   Best____Dale Erwin

> 
> 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? 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? 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? 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? 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
> 


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