I have a large slab of spalted maple that I planed about 6 months ago, meant for a live edge bench with a spindle support backrest, and a work in progress ever since. The slab is about 21'' wide and close to 9 feet long at about 1.75'' thick. It has been drying for 2.5 years outside and the six months inside if not more. I thought it was good to go, but my basement is moist in the summer and since cooling off the board has twisted/popped up at one end and a twist at the other. I placed it on some shims to determine a 'level' top, and what spots balanced at what heights and tried find a happy compromise for all the different angles. What I got was leg lengths that varied within half an inch, but that half inch occurs over the 21'' width dimension. So you can imagine that placing a router on it and drilling a hole will not make a mortise for the tenon that is perpendicular to the ground.
I have been a little stumped over this one and thought I would put it out there. Thanks in advance.