Hygrometer

[Ron Nossaman]

>Ron,
>         If one were to strive for and "for the sake of discussion" 
> achieve that absolute accuracy how long could the board be expected to 
> stay that way after it is removed from the "hot box" for working? If I 
> took the board out and got a little side tracked and didn't get to gluing 
> my perfectly formed ribs on until say an hour or two later ... am 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 
be assembling the soundboard in a rigidly humidity controlled room, and you 
could take as long as you wanted - if you didn't breathe too much. In the 
real world, it depends on a couple of things. How much string load are you 
counting on the panel supporting, and how much the ribs? What's the 
difference between your target temp & RH% (indicating MC in the panel) and 
your work area temp & RH%? If you've dried your board to say, 6% MC, and 
your shop is 70° at 30%RH,  then you have lots of time. Eat lunch. Take a 
nap. If the shop is 80° at 75%RH, then you'd probably better consider 
drying it down again.

As an experiment some years back, I made a little MC gage out of a cross 
grain strip of new soundboard spruce, with a thin strip glued cross grain 
to one surface after I'd cooked it dry in the oven. Then I mounted it on a 
base so it cantelevered out over the base on edge. I marked on the base, 
where the end of the strip was while it was still dry. It bowed nicely when 
it re-hydrated. I started drying it down with my panel when I did 
soundboard replacements or repairs to see if it would make a dependable MC 
gage. It doesn't seem to be bad at all once you get it reasonably 
calibrated. I still use it as an indicator of whether or not I've dried the 
panel long enough after I reached my target temp & RH, for the wood to have 
caught up. I found that what we've been told is true. Wood does seem to 
absorb humidity faster than it releases it, but it's tough to tell how 
quickly it's doing either in the shop. So the best way I know of to tell if 
your board has been out of the box too long is to check your home made MC 
gage and see what it says.

Ron N