Tables like these, and any wide tables really, should be properly battened. The base helps to do this and this is one of the things often ignored by metal bases.
Most tables made like this in Japan, where they are very common but typically well made, are made with sliding dovetail battens. They will usually not do anything more than an oil finish, but when properly battened they tend not to do strange things.
I don't usually build really wide tables from one piece, but all of those that I have built are still quite flat.
It's also common now to make these tables out of exceptionally thick material, not sure why that is but it does a disservice to the structure. If you keep the table to around 1.5"-1.75" thick it'll make life easier for the table as the structure will be able to effect it with a greater chance of success.
Last edited by Brian Holcombe; 12-09-2017 at 11:14 AM.
Bumbling forward into the unknown.