Place the reclaimed wood planks on the floor parallel to one another. Set the 2-inch-thick by 2-inch-wide by 28-inch-long pieces perpendicularly across the reclaimed wood planks. Set the 2-inch-thick by 2-inch-wide pieces approximately 4 feet apart, centered in the middle of the 8-foot-long boards and drive screws down through the 2-inch by 2-inch pieces and into the 8-foot boards.
Attach the legs to the harvest table while assistants hold the tabletop. Place the 4-inch by 4-inch square ends of the tapered wooden legs flush into the corners of the tabletop. Drive four finishing nails down through the tabletop and into each table leg to hold the leg securely to the table.
Set the finishing nails into the tabletop with the nail set tool. Place the nail set on the nail head and hammer the wide end of the nail set. This will bury the nails into the surface of the wood without causing marks from the hammerhead.
Slide the 3-inch-wide planks into the spaces between the legs and flush against the bottom side of the tabletop. The 7-foot and 4-inch pieces will set between the legs on the 8-foot-long side of the table while the shorter 2-foot and 4-inch long pieces will set between the legs on the narrow end of the table. Drive finishing nails down through the tabletop again and into the pieces and set the nail heads.
Paint several clear coats of polyurethane onto all surfaces of the wooden harvest table. Allow drying in between each coating and before use; the coats will protect the wood from water damage when used to place foods and liquids of varying temperatures.