36"x36"x3/4" MDF Spoilboard with 2" grid

Fusion 360 version -
The bottom is cut first using a .25" end mill.
First it cuts two 3/8" registration holes through the spoil board and into the Mill Right MDF base. When you flip the board over to cut the top, use dowels to locate the board in the same exact spot.
Second, the bolt clearance holes are cut then the recesses for the T-Nut heads.

Flip the board over and run the set up to finish the clearance holes. Then switch to a 90 degree V-Bit to cut the 2x2 grid.

T-Nuts are from Amazon and are 1/4"-20, 5/16" long with a 3/4" head.