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I'm designing a c-table with ~1 meter overhangdesign

Tabletop is 30-40mm thick walnut slab, column and legs are (glued) walnut boards, 40mm thick. How do I connect a tabletop to a column, that can withstand 500 N*m of momentum of a kid sitting on a tabletop. The connection needs to be disassemblable for transportation ~10 times in a lifetime. Preferably with less of metal showing on the surface.

My current idea is inserting 180-mm long , 12mm diameter metal dowels, with threaded hole at the end for retrieval. enter image description here

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  • Did you thoroughly search for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer! woodworking.stackexchange.com/help/how-to-ask
    – Graphus
    Commented Oct 23 at 6:12
  • I strongly suspect that even with the beefy material you're building with that no joint that isn't additionally externally supported will be sufficient here, due to the 1m tabletop. Knockdown joinery tends to be inherently less stiff/stable than fixed joinery (especially in contexts where it doesn't receive additional help from other joints or structural elements, as is very much the case here) and with a substantial cantilever like this the difficulty goes up to 11.
    – Graphus
    Commented Oct 23 at 6:24
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    I would worry more about the stability of the whole table, especially with a (potentially moving) child on it, as part of the table seems to be outside of its support polygon with this legs design.
    – Thierry Lathuille
    Commented Oct 23 at 12:11
  • @Graphus, I've edited my post, would add FEA modelling later
    – Gleb
    Commented Oct 23 at 14:08

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This question presents a complex set of considerations that may not be solvable outside of actual experimentation. Woodworkers usually don't work with Nm, so outside of someone like a structural engineer/woodworker, most of us will not be familiar with the problem as presented. (How much does the child weigh?) They will have ideas on how to assemble a good candidate design. Based upon your sketch, there are some considerations to address in refining your design:

  • The opening in the seat for the post is too close to the edge of the slab and any force applied to the seat would rip out the end.
  • Considering the thickness of the seat there is not enough vertical contact with the post to transfer the force to the post. A triangular center brace under the seat would increase the strength of the seat/post joint. The connection between seat and post will want to rotate and needs strong connection at the top and bottom of the junction to transfer the loads. A similar problem exists at the base where the post connects to the horizontal cross braces. The center of gravity for the assembly will constantly change as the child moves.
  • It is not clear how disassembled you want to make the assembly. All of the connection joints will be under constant, changing stresses. The more permanent the connection, the more durable the assembly will be. There are woodworking joints that can disassemble, such as mortice joints with thru tenons and loose wedges.
  • In planning a design based upon your sketch I would be looking for joints using mortice and tenon type connections with limited or no disassembly requirements. The more I could use tight, larger area joints with glued connections, the better. I would look to create base legs and seat supports with as much vertical dimension as possible at the post.
  • If the post is to be removable, I would provide a sleeve of wood that is securely attached to the seat and slides down outside the post as far as possible.

I would suggest that you begin searching for other examples of similar tables online and begin refining your design. You can then post questions on the specific concerns you discover regarding the design here to get clarification and refinement.

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  • what's your feeling of the required size of the brace and the edge or the sleeve? The question is about particular post-to-tabletop joint, others are not as loaded, and/or have more surface.
    – Gleb
    Commented Oct 25 at 8:11
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    @Gleb I would make the outer depth at least 1". The depth at the post is more problematic because we must account for the type of connection. as well. Is it mounted at the side with screws to be removable in which case it must be high enough to allow connections at top and bottom of the connection face, or is it glued solid in a mortice and tenon connection? My gut would be at least 4" for glued and maybe double that if screwed. OF course, my gut tells me to make the whole thing without removable joints since it is not too large to be moved as a whole.
    – Ashlar ♦
    Commented Oct 25 at 16:18
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    @Gleb ...I would encourage you to come back for a further review once you have developed your design further.
    – Ashlar ♦
    Commented Oct 25 at 16:19

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