Both the garage workbench (12' x 4') and the one in the basement had twists and warps in them, so I spent 10 hours over 3 days correcting the problem. After installing leveling bolts in all legs and leveling the frames as much as possible, I removed the tabletops, snapped chalk lines along the frames as a guide, planed the frame in the basement table as necessary, and reinstalled the tops with shims as needed. Used a 4 foot bubble type level.
