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Avoiding Warp in a Glued-Up Panel
Question
I'm getting ready to build a table. A woodworker friend told me when I glue up the top, I should alternate the orientation of the boards. Another told me it doesn't matter which way I place the boards. Who's right?
Kevin Michaelson
Lawrence, KS
Answer
Actually, neither of your friends is wrong. They're talking about orienting
the boards so the growth rings visible in the end grain arc up on one board
and down on the next, or all arc consistently in the same direction.
If you alternate the boards, your panel should remain flat across its overall width, as each board cups in the opposite direction. But the panel surface may feel wavy.
On the other hand, if you glue-up the boards with the growth rings all oriented in the same direction, the whole panel may cup in one direction. The surface remains smooth to the touch, but the entire panel may take on an arched shape.
I pay attention to the growth ring patterns, and try to alternate every other board. But I pay more attention to each board's face grain appearance. If I have to, I'll orient adjacent boards with the growth rings pointing the same way in order to get the best looking panel.
Also, make sure you apply an equal number of finish coats on both sides of the table top. This helps keep any moisture absorption or loss equal on both sides, further reducing the likelihood of warping or cupping.
