Q: I have been drying wood for many years and all of a sudden I have had a complaint about what the customer calls longitudinal stress. When they rip an 8-inch-wide, 12-foot-long, 1-inch board, the two pieces, when they put them back together, will have a gap between them of about 3/4-inch in the center. The traditional clothespin stress test shows "no stress." Any suggestions?
A: Your description does indeed sound like longitudinal drying stress. As we process more lower-grade lumber from closer to the center of the tree, we are beginning to see more lengthwise or longitudinal stress. Plus, I think that many customers are getting more exacting in the quality requirements and testing. These two reasons may explain why you didn't hear much about this stress in the past.
Incidentally, the "clothespin" stress test does not measure longitudinal stress, but measures across-the-grain stress. The two are not related, so you can have one without having the other. This is why your conventional stress test looked okay.
In order to relieve longitudinal stresses, you need to condition the lumber at 180 degrees F and obtain a 10 degree F depression within a couple of hours. The depression is where most folks fail - they set the instrument for 10 degrees F, but because of the heat in the steam, they actually achieve 15 degrees F.
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