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I made a table and screwed the panels together via two separate wooden bars and even with one aluminium bar. I did that in the base room. Now the table is in my flat and the panels are moving away from each other though I used large and thick bolts.. why is that?

The table from bottom:

Table downside: Bolts and one bar

Table from top

Table upside

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The short answer is the wood is shrinking as it loses moisture. Because you've used two fastening points across the width of a top board, one or more of those top boards may split as it continues to shrink.

Accommodating this sort of change in dimension (which continues to happen seasonally, even when the wood has fully "dried") is one of the classic challenges in constructing furniture from solid wood.

There is a lot of literature out there on this topic. Here's the first link returned from Google on "furniture accommodate wood shrinkage" https://www.extension.purdue.edu/extmedia/fnr/fnr-163.pdf

Note that it's both shrinkage and expansion that cause problems.

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  • Great answer, thank you! Can you please also advice something? Shall I disassemble it and let it work for some time? – Ben Dec 3 '17 at 14:53
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    I think you could leave it assembled. You might want to take out some of the attachment screws, or at least loosen them, such that each board is only held by one screw at each attachment location along its length. The shrinkage will be mostly in width, and what you're trying to do is avoid two screws working against each other to counter the shrinking; that's what would cause splitting. A year of "seasoning" is probably plenty. Note the boards will still expand and shrink with seasonal changes in humidity. – scanny Dec 3 '17 at 20:20
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As scanny states in his answer

There is a lot of literature out there on this topic.

To expand some on that answer.

Wood is always in a constant state of flux when it comes to moisture. A general rule of thumb for green wood is to sticker it for a year per inch of thickness which helps it maintain is shape. That is a loose rule that can be quickened with other means like kilns and such.

When working with solid wood (not green) it a good idea to leave it in the environment it is going to live in for at least several months to acclimatize. Doing so will greatly reduce the rate of change. Be prepared to have to have to prepare the wood again because of warping and understand though that it is in a state of constant change that can never truly stop.

How wood shinks and expands is a science in itself. For a simple introduction look at the following image that shows where the greater change, in general occurs, in lumber per the grain direction.

Rate of change according to plane

You can also get a basic idea of the types of warping to expect based on the cut of lumber as well.

Warping according to cut

Both images from workshopcompanion.com

Forcing the wood to stay in place with hardware can work but could easily exacerbate the shrinking / expansion issues and force it to split.

This is why you see things like floating breadboard solid wood tabletops. Those might be worth looking at for future projects. You will see plenty of plans that don't do that. Some of them might last forever without issues. However, there are plenty of stories of people that make great projects just to have them fall apart season later.

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  • great information! – Ben Dec 9 '17 at 10:01

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