I am in the process of building a dining table out of solid walnut. I don't have the skills or equipment to make the tabletop myself, so I got my wood supplier to do it for me. The tabletop is 6/4 walnut, 7' long by 40" wide, and is made up of 6 smaller boards glued together. The shop is reputable and seems to know what they are doing. I received it about a month ago, and since then, it's been standing behind my living room couch leaning against the wall (long side on the floor). It was leaning at maybe a 10 degree angle, with the underside of the piece facing away from the wall.
Anyways, now that I've completed the base, I'm paying attention to the tabletop, and I notice that there is some significant cupping. The concave side (the underside) goes in about 3/16" in the middle down from the edges.
Unfortunately, I didn't check for cupping when I initially received the piece, so I'm not sure if it came like this or if I caused it myself somehow. Regardless, the damage is done, so what are my options now?
I've seen some articles/videos where they dampen the concave side of a cupped board and let it sit overnight to straighten it out, but will that work on my 6/4 tabletop? I tried applying this technique yesterday evening, but this morning I don't measure any difference in the amount of cupping.
Any advice would be greatly appreciated.
Note: I don't have a table saw, thickness planer, or jointer.