Hygrometer

[Greg Newell]

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Ron,
         If I correctly understand what you are doing with your=20
sophisticated :-) setup, you are looking for a change not necessarily a=20
specific number from your meter. Correct? Do you feel that you can=20
adequately state the moisture content of the wood from an instrument=20
designed to measure the air simply because it is against the wood and=20
trapped under a blanket? What would happen to the measurements if you=20
introduced , say, a 6" air pocket around the hygrometer instead of having=20
the blanket on top of the meter? Do you think that the readings would be=20
different? the environment you create with the space heater under the piano=
=20
is not necessarily the same environment above the board . Would you agree?=
=20
If you measured the MC under and over the board they would surely be=20
different, right? Could it be possible that some degree of instability is=20
possible because of this? I know the board is relatively thin but without=20
air circulating around the top could there be potential problems with=20
uneven rates of contraction of wood fibers? Would this cause future=20
problems with cracks or is this all semantics and nothing to worry about.=20
Thanks for your indulgence of my random thoughts!

Greg


At 04:52 PM 8/30/2002, you wrote:

>>Ron,
>>         If one were to strive for and "for the sake of discussion"=20
>> achieve that absolute accuracy how long could the board be expected to=20
>> stay that way after it is removed from the "hot box" for working? If I=20
>> took the board out and got a little side tracked and didn't get to=20
>> gluing my perfectly formed ribs on until say an hour or two later ... am=
=20
>> I too late? do i need to start the process of drying it down all over=
 again?
>>
>>Greg Newell
>
>
>Greg,
>I'd say, presuming the need for absolute humidity control, that you would=
=20
>be assembling the soundboard in a rigidly humidity controlled room, and=20
>you could take as long as you wanted - if you didn't breathe too much. In=
=20
>the real world, it depends on a couple of things. How much string load are=
=20
>you counting on the panel supporting, and how much the ribs? What's the=20
>difference between your target temp & RH% (indicating MC in the panel) and=
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>your work area temp & RH%? If you've dried your board to say, 6% MC, and=20
>your shop is 70=B0 at 30%RH,  then you have lots of time. Eat lunch. Take a=
=20
>nap. If the shop is 80=B0 at 75%RH, then you'd probably better consider=20
>drying it down again.
>
>As an experiment some years back, I made a little MC gage out of a cross=20
>grain strip of new soundboard spruce, with a thin strip glued cross grain=
=20
>to one surface after I'd cooked it dry in the oven. Then I mounted it on a=
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>base so it cantelevered out over the base on edge. I marked on the base,=20
>where the end of the strip was while it was still dry. It bowed nicely=20
>when it re-hydrated. I started drying it down with my panel when I did=20
>soundboard replacements or repairs to see if it would make a dependable MC=
=20
>gage. It doesn't seem to be bad at all once you get it reasonably=20
>calibrated. I still use it as an indicator of whether or not I've dried=20
>the panel long enough after I reached my target temp & RH, for the wood to=
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>have caught up. I found that what we've been told is true. Wood does seem=
=20
>to absorb humidity faster than it releases it, but it's tough to tell how=
=20
>quickly it's doing either in the shop. So the best way I know of to tell=20
>if your board has been out of the box too long is to check your home made=
=20
>MC gage and see what it says.
>
>Ron N

Greg Newell
mailto:gnewell@ameritech.net
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