OK, I adjusted the table dimensions to severely minimize sag, but still want to go for that stretcherless, trestleless, "minimalist" look. Using red oak, will edge join (maybe w/ biscuits, maybe not) 16 3"x1"x72" planks for a 72x48x1 top. If I join these right and true, the top itself should be sufficiently sturdy of it's own accord for dining table purposes (the wood is about 80 pounds, I tested 280 pounds on the sagulator and still get less than 'visible' sag, with legs at the very corners. That seemed like not enough sag to be anywhere near failure, ihmo. Anything really wrong with that logic?
Even so, if we could assume for a moment I could design a such a top, I would like to place the legs about 6" from each corner. Each leg will be 3 1x3's laminated together. Since I'm going for no stretchers or trestles, I have the following idea for joining the legs, which is kind of a dado/through tenon hybrid:
top view: long side x-section: short side x-section: (long side) |-----------| |------------| |-------------- | | | | | |---| |---| | | | -------|| ||------- ---|| ||------ |----+++++++--- || || || || | +++++++ -------|| ||------- ---|| ||------ | +++++++ |---| |---| | | |----+++++++--- | | | | | | | | | | |-------------- | |
After laminating the legs into the 3x3 dimension, I'll make 2 1"x1" dadoes, 1" from the top. The table top plank which this leg is attached to will actually be 3 planks, one between the legs, and one between each of the legs and the end of the top. So, the top will actually be assembled with 2 of the planks being shorter, so it appears to have 4 notches. The legs will go into these notches, with one dado facing the end of the short plank. Then the "really" short plank will go with it's end into the other dado, and it's edges matching the surrounding 2 planks.
If I match the edges well enough and use good glue technique, I would think the legs would be pretty darn sturdy for a dining table. Does this sound reasonable?
The final issue is movement - namely the top planks 'wanting' to expand/contract (tangentially) as much as .10" more than the legs (radially) if they are both plainsawn. I don't know if I can negate these or not.Even if the glue holds, it might cause a split in the top plank somewhere. Applying enough tensile force to stretch a 3" plank by .10" seems like enough to split it to me, but that's based on totally uninformed guessing, not hard calculations - which I'd be interested in learning how to do if someone could point me to a good book with the relevent engineering education in it. Also, the legs will tangentially expand/contract against the dado joints, but with this design, that movement would only be about .03" unrestricted, as it's 1" of wood thickness in this plane as opposed to 3", so I "think" this wouldn't be a problem.
-Chance Casey