I'm looking to build some table legs with a double X design.
The top is about 40" wide (round) and weighs 120lbs. I should think that 4x4 posts should do it, but maybe they need to be bigger? I can find many how-to documents about building a single X design by notching half of each post, but the double X seems more complicated if I want it to support the weight of the top and everything placed on it.
Here is one way, although it is a little bit difficult to show in a simple sketch. Sorry, but the cross section sketches show the joints horizontally instead of in vertical orientation. Give me some feedback if this is not clear enough.:
The legs do not have to be 4" to support the weight, but they may be needed to get the 4-way intersection to work.
Two legs in one plane act as the primary assembly and are lap-joined with a notch in each leg to allow them to cross each other.
Next the opposite legs do not cross through. Instead create a 90 degree joint with a spline (dashed line) centered in each leg to support the 90 degree bend. (Shown in red). These legs will set in a mortise cut (not shown & narrower than the full leg width) into the sides of the primary legs (black lines).
A section through the combined legs is shown below.
The primary and secondary legs can be joined in a glued joint provided the boards are in good contact with each other. Otherwise consider some through dowels to reinforce the joints. I strongly suggest that you make a test model before attempting this for the actual project. There are bound to be complications that you did not consider that can be worked out in a test.
If it were me, I would probably start by making 4 half-X's that are half-lapped. Then miter them all together. The glued half lapped half-x's oriented vertically will support the weight of the top, and they can be mitered together, and even doweled or connected using a floating tenon at that point as well.
