I'm thinking of making a 4 x 8 foot dining room table top by gluing together two 9/16" thick layers of solid walnut with a 1/16" cross-grain walnut veneer in between the two 9/16" layers and then putting it in a vacuum bag. By doing this I would hope to minimize or eliminate seasonal expansion and contraction. Has anyone tried this? Is it a good/bad idea?

I don't think you will find someone who has done this, but who knows? How much stress will be in the table top will depend on the annual RH swings in its location. If this is for a client, I would not do it. Too much risk with an unknown procedure. If it is for yourself, go for it and tell us how it works after a year or two.
I would choose epoxy for this layup or another adhesive with little or no moisture otherwise you will be fighting with curling layers during roll out. I would consider a five ply glue-up instead by adding 1/32" or 1/16' veneers to the top or bottom and having the thick layers as the cross grain. This will balance the glue line stresses to both sides of the thick layers.
As a last thought, this is a lot of added work over a single solid layer of 1 1/8" walnut or a core and veneer. Is the extra effort and risk necessary to the outcome?

You will never prevent seasonable movement with wood that is 9/16" thick. My feeling is that the inner veneer layer will be split into pieces when the thick wood expands. 4' is a very wide table and difficult to pass food across. I'd forget the lamination and use quarter sawn walnut that is milled to the thickness you want. It's been done for centuries, no need to feel like solid wood will never behave all of a sudden.

I disagree with Rich. We regularly make 7 ply panels with two solid layers 5/8" thick. This is done mostly in Mahogany or White Oak. 7 years and no problems yet. Many of these panels replaced solid wood panels made with Titebond III that came apart with exposure to heat - normal environmental conditions.

We have 7 ply samples laying in the downspouts that have been there for 8 years, and they are a little rugged, but are as tight as can be. Each layer is intact, and the layers have not peeled or buckled.

Now, these are door panels, so the perimeter is retained in the frame and movement of about any kind is limited. But the 7 ply system works wonderfully.

I can see it would work well as a table top. In general, the more plies the more stable.

Bad idea. That table will expolode or warp to heck.
Use solid wood.

Bad idea. That table will expolode or warp to heck.
Use solid wood.
Sounds like a make work project.

Aren't you comparing apples to oranges David? I agree that 7 ply will react much differently than 3 ply.

Apples and Oranges go together in the nice turned bowl in the center of the table. But seriously.....

Yes, the more plies, the better stability. A 3 ply with 2 - 9/16" thick layers would be pretty dicey. No telling how it would come out. I would do the top as a solid wood table, as long as I knew the lumber and who and how it was dried. Any insecurity, I would go for 7 ply, and the sure thing.

The reason we developed 7 ply panels for our doors was the "Sure Thing". We had to avoid any problems with panels, and we could not do so even with the great wood we buy.

The OP says he wants to do the lamination to minimize or eliminate seasonal expansion and contraction. A reasonable response to a reasonable design issue. But, I would either choose solid wood carefully, or a 7 ply lamination. And yes, that 7-ply lamination would be monster to get into a vacuum bag.

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Why has no one mentioned a standard veneer over plywood or MDF approach? Take your wood and slice it into 1/16 to 1/8" veneer. Seam it and glue it to the substrate with UF glue. This is a system with decades of history, all good.

John

I think using Solid wood will make your table strong and it also provides good finishing.