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I want to attach two 5'6" red oak boards together as part of a table, both 3" x 0.75" at a 90 degree angle, like this:

enter image description here

I was planning on gluing them and adding some pocket screws on the inside, since it'll be hidden.

I'm not sure if this will cause problems in the long run if the boards expand or contract. I'm also not sure if the pocket screws help at all, or if they're redundant as long as I clamp it enough.

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  • Chris, you should already have read about wood movement and how it relates to this (not just here, although it's amply covered here) but pretty much anywhere that covers the topic at all reliably. There's no wood movement to speak of longitudinally. – Graphus May 11 at 0:08
  • "I was planning on ...adding some pocket screws on the inside" Sure if you want to use the screws as clamps, but they're not needed for strength. Again covered amply in relevant Q&As, a well-done glue joint along the grain like this is literally stronger than the wood around it. Hence the common (but inaccurately worded) phrase "glue is stronger than wood" (the better understanding being covered in this Answer, among others). – Graphus May 11 at 0:14
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The top board will expand left to right, but not significantly in the relatively small area of the glue joint itself. The bottom board will expand up and down, but not significantly in thickness.

You can do the joint purely with glue if you desire - joints were glued only for a long time. Screws can be added but aren't necessary. Think of them as additional clamps for while the glue sets up. The only difference is that you don't remove them when the glue has dried. If you expect a large amount of stress on this particular joint, for example, you expect someone or something to be pushing against that bottom board with notable pressure, then some screws would provide extra confidence that the joint won't come apart.

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  • Interesting, I was concerned about the boards expanding lengthwise. Does that not happen as much? Or is it fine because they'll expand lengthwise at the same rate? – Chris.B May 10 at 19:48
  • The vertical piece is the table apron. The legs will be inside the apron and bolted to it, so I don't think the apron will have much ability to move if someone pushes or pulls on it. So maybe I'll skip the screws, unless they help me to keep the two boards lined up while I'm gluing it – Chris.B May 10 at 19:51
  • @Chris.B Wood does not appreciably expand along its length so you need not worry. While he wood expands slightly differently with the growth rings and across them, the difference is negligible and you can glue together without concern for any internal stress. – Ashlar May 10 at 20:06
  • Well that's a relief. I was worried that my entire table design was going to fail because I hadn't accounted for expansion. Thanks! – Chris.B May 10 at 20:08

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