Oops. Yesterday I grabbed the shelf panel that I had carefully flattened a few days ago, and found that it had suddenly developed a really nasty cup. This was kind of a surprise to me. The wood had been stickered since I milled it about a month ago, and hadn't shown any signs of movement during that time.
Here's what I think happened: After flattening the panel, I put it up out of the way, lying flat on top of a sheet of plywood. Soon after that, the ambient humidity took a rather abrupt nosedive. So I'm thinking that the top surface of the panel, which was exposed to the hot, newly-dry air in my garage started to lose moisture. Meanwhile, the bottom surface couldn't dry out as fast because it was against the plywood. The direction of the cup was consistent with this fine theory.
The panel is now undergoing a three-step recovery program. (From what I hear, the twelve-step programs take a long time and involve lots of meetings. Nuts to that.) First, I set the panel up on some sticks so that air can circulate freely all around it. Then I dampened the concave side in the hope that it would reabsorb some of the moisture that it had presumably lost. That actually helped a lot. Finally, I applied some friendly persuasion in order to discourage further movement as the moisture content stabilizes.
I guess time will tell if this plan works or if I need to make a new shelf one of these days.
Nothing like pipe clamps an 2x8 s. you live in AZ, an have rapid swings in humidity. That is tough to deal with. Like back east in the very dry heated homes in winter. Here in central CA it is dry but moe constant.
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