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Edit: I withdraw the question but am leaving it up for posterity. Based on comments, I think it is is malformed. I reframed it as a "what joinery should I use" question here.

Like most new posters to this forum, I am building a bunk bed. I'm hoping someone here can suggest improvements to the joint I designed to attach the mattress box to the posts.

In broad strokes I'm using pine, 4x4 for the posts, 2x6 for the mattress boxes, 2x2 for the cleats, 1x4 for the slats, and 2x4 for ladders and guard rails. I'd like to build the boxes as permanent units and knock it down by removing the boxes from the posts. The structure is roughly this and the joint in question is this:

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My idea for the joint is a half lap to make the box corner and a dado to hold it up (slats removed for clarity):

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My theory is that the weight goes mattress -> slat -> cleat -> long box side -> post. So I expose a the maximum amount (3 ½") of the long side to the dado and keep it in compression. Then I half lap (1 ½" square) and screw (peg?) the short box side to the long since it isn't load bearing, the slats will hold the box square, and other pieces will hold the posts square. Finally I secure the dado with a bolt.

So:

  • Is there a better design to achieve this that is no more complicated than a dado or half lap?
  • Do the bolt/screw/peg locations look right or am I undermining the wood's strength?
  • Is one bolt per post enough to keep the box attached to the post? What size bolt should I be using?
  • Is one screw + glue enough to make the box corner permanent?
  • Can I use a peg instead of a screw to make the box corner?

Thank you!

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  • Did you come up with this design completely independently or is it based on something? If it's the former, as I always say in a situation like this, don't reinvent the wheel. It's both unnecessary and often undesirable. If this were a dining table or something else relatively non-critical it could be a perfect opportunity to try some innovation in joint design, but where strength is critical it's important to use established joinery (and there're a few to pick from) unless you really know your materials, and have practical experience to draw from.
    – Graphus
    May 5, 2023 at 4:59
  • And, there are far too many question marks here. Questions should, as much as possible, have one question in them; maybe two if the second is directly tied to the first. But ideally it's one query per Question. Anything parallel or tangential, if it's worth asking in the first place it's worth a Question of its own, and it helps make the Q&A findable by future searchers. Also, your first bullet is a bit too open-ended for the SE model (and of course could be likely to attract subjective answers, which is a no-no).
    – Graphus
    May 5, 2023 at 5:06
  • @Graphus Yeah, now that I'm reading it again, you are exactly right. I'm asking the wrong question. The question should be "which existing joint will do what I want." I'll take this down and re-post. Thank you!
    – LoftyGoals
    May 5, 2023 at 12:04
  • @Graphus Which is why there were so many parts to the question (which I think I should mark with a banner rather than take down).
    – LoftyGoals
    May 5, 2023 at 12:13

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