MC gage experiment

[Ron Nossaman]

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>Another way to do it is to simply weigh a sample piece of spruce. Using 
>the electronic balance I use for action balancing work (goes to 0.01 
>grams), I simply weigh one or two 100 gram or so pieces of spruce to 
>monitor when the weight, and hence MC, has stabilized.

That works very well. I just wanted an easy way to sidestep the part with 
the scale and the math.


>One nice thing beyond the weight monitoring method's simplicity is that 
>you can use samples cut from the same stock you made the panel from.

This is true, which brings up something I've wondered about but haven't 
gotten around to trying to test. Looking at individual planks that have 
twice the number of annular rings per inch at one edge that they have at 
the other, I've wondered what the difference in moisture transfer rate 
might be between the two, if there is any difference. Have you ever tried this?


>  Bottom line, you just simply need to know what initial MC your wood is 
> if you are using a gauge.

Well, no you wouldn't, any more than if you weighed samples. Everything 
goes into the box, and you don't use the lumber until everything in the box 
is stabilized at your target MC, whether you're measuring, weighing, or 
looking at an MC gage. Weighing samples and measuring doesn't tell you the 
initial MC of the wood either. It just gives you a point of reference 
against the changes that occur in the conditioning box. You're still just 
waiting for repeated weight and measurement readings to quit moving, 
indicating that the wood is at the MC the temperature and RH% inside the 
box dictates. With the gage, I don't need a linear measurement, weight, or 
even temperature and RH% to compute MC. When the gage stabilizes with the 
lumber in the box, which I can ascertain by looking at the gage, I'm pretty 
close. My inept attempts with various MC measurement methods have pretty 
much convinced me that pretty close is the best I can realistically hope to 
get by any method I've tried, so this pleases me because it's simple enough 
for me to handle. This same gage effectively eliminates the need to 
precisely know the RH% in the box, since it's a direct reading of the 
linear dimensional changes corresponding to the MC of the wood in the gage. 
I'm normally as suspicious of self contained, self referential systems as I 
am of highly instrumented and exceedingly complicated ones requiring lots 
of steps and computation, but this seems pretty straightforward to me. Put 
the gage in the box with the lumber (or panel) and turn on the heat. If the 
lumber is wetter than the gage, the gage reading rises to meet it as the 
lumber MC is coming down because the gage is absorbing moisture the lumber 
is giving off. Adjust heat minutely over the next few days as necessary to 
zero in on the desired MC reading on the gage, and keep it there for at 
least a couple of days once it has stabilized. True, you don't know the 
precise moment the lumber reaches EMC like you might (depending on the 
thickness) with measurement and weight, but I'm not scheduling production 
that close anyway.


>You can do that reasonably well by drying in an oven and weighing 
>(although I find the accuracy of this method to be a bit wanting).

I tried this too, with confusing enough results that I abandoned it with no 
regrets.


>David initially asked about quick drying methods. I think monitoring 
>weight and/or panel width are fine methods, but I also think it is 
>advisable to be patient and give the system a little extra time to be sure 
>you have reached your target EMC.

I agree. Quick is touchy and questionable, to my mind.


>Employing two of these methods would be good insurance. If you are really 
>trying to do this quickly - like you've got a tight production schedule - 
>IMHO, you need a system like Ron O's and some real good, properly used, 
>electronic equipment to accurately monitor the process. There is much 
>known about kiln drying wood. If you want to keep it simple, and I think 
>any low-volume shop can do that, you need to give a panel a week or two to 
>dry and stabilize in most situations.
>
>Terry Farrell

Again, I agree.

Ron N

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