I have finally completed my 40", 1 1/4" solid planked beechwood round table top. I cut a 36" square for an open shelf about 6" below the top. I have cut 2" circles from the 4 corners in such a way that the legs have to be slid in. The legs are 2" round. My objective was to incorporate the legs into the square to make it appear as a rounded cornered square, as opposed to a haphazardly thrown together mess. I was very lucky that it worked. The fit is tight enough that the square can almost stay suspended.
I'm clear on attaching the legs to the table top. While the table is upside down, I can slide the shelf down.
My question is, though I have a couple of ideas, I would like to know if there is a customary way to attach the legs to the square. I've made tables before, but never added a shelf.