[dataway]

Hot rolled 1/2". The bolt/nut setup allows you to apply a LOT of force to the plate either up or down, to adjust about an 12" radius of surface while applying very little movement to adjacent areas. It's a tedious process to flatten. Some of the countersunk screws you see on the top are pulling down, and locked with the nut below, other areas are raised with the nut below and locked with the screw above.

I should have set up the frame to have these adjustments points about 3" from the edges of the plate instead of about 8". I don't have enough control of the edges of the plate to get better than 0.20" in those areas.

Not real obvious from the photos but the screws on top are threaded into the nuts welded to the frame, there is another nut between the bottom surface of the table and the nut on the frame. They are like little machinery jacks that will either lift or pull down on the plate.

I need to buy a good 8 foot straight edge to really check it properly, something better than typical Home Depot, so pricey.

[Shiny]

Understood, thanks!