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I measured every thing correctly. All the legs of the bench were the same at thanksgiving but now are half an inch different at Christmas dinner. Is there a way to stop wood from expanding and/or contracting? Is there a way to keep fresh wood from warping even after the “bench” or furniture item is built? Please help.

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    The solution is obvious: Build one table for Thanksgiving and another Christmas. Problem solved. :) Seriously, though, I'm very interested in answers to your question. Dec 26 '20 at 22:52
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    Hang on a second, legs can't normally change length (either positively or negatively) because wood movement along the grain is so tiny it's pretty much always ignored. So I presume the legs have the grain running horizontally? If so there's your answer right there — wood expands and contracts across its width as its moisture level goes up or down.
    – Graphus
    Dec 27 '20 at 1:08
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    @Graphus My assumption was that the legs are staying the same length but the rest of the structure is warping to make them uneven...Though I think we really need more information here to know what's actually happening. Dec 27 '20 at 16:36
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    Thanks guys, the leg are indeed the same length. It is because the horizontal one warped. If I knew how to put pictures on here I “wood.” Little humor there...
    – Sparky
    Dec 30 '20 at 19:44
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Is there a way to stop wood from expanding and/or contracting?

The main reason that wood changes dimensions is changes in moisture content; generally, it expands a bit in directions perpendicular to the grain direction in more humid summer months and contracts a bit in the same directions in the dryer winter months. There’s very little change in the direction parallel to the grain.

One way to prevent this movement is to seal the wood, so that moisture can’t get in or out of the wood. The more completely you seal the wood, the less movement you’ll see. However, most finishes don’t seal wood so completely that they stop seasonal movement.

Another option is to prevent the fluctuations in humidity. If you can keep the humidity constant, perhaps using a humidifier in dry months and a dehumidifier in humid months, there should be no movement. This is an option that you might find in museums, but not really practical in most homes.

A third option is to not stop the movement at all, but rather to accept it and plan for it in your designs. This is by far the most common approach that woodworkers use. It’s the reason large panels often float in frames, and it’s why table tops aren’t glued to their bases.

All the legs of the bench were the same at thanksgiving but now are half an inch different at Christmas dinner.

We really need more information to understand what’s going on here, but seasonal movement doesn’t sound like the culprit. Bench legs are usually created such that the grain runs vertically, parallel to the leg, and there’s no wood that shrinks 1/2” in that direction over the 14-18” of a bench leg. Furthermore, benches usually have four or more legs that all have the grain running in the same direction, so even if you did somehow build a bench where the grain runs horizontally in the legs, all the legs should be affected by seasonal movement the same way.

More probable explanations for your problem are either that the rest of the bench warped or twisted, or that the floor isn’t flat. Even a small amount of twist could easily push opposite legs up or down, and with three legs on the floor all the change would appear to be in one leg. Likewise, a small hump in the floor could be magnified by the length of the bench. Try moving the bench to a different spot; if the problem remains, the bench has probably twisted. If the problem goes away, check the floor.

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    You’re exactly correct. Thanks for your input. You covered all the bases. Thanks again
    – Sparky
    Dec 30 '20 at 20:16

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