Set up the five 2-by-12s next to each other to form a square that is evened up on all sides. Glue them together and let dry. Lay the 52-inch 2-by-4 across the middle of the boards and screw it into each one from the top.
Mark the center of the wooden square by drawing lines corner to corner and marking the intersection point. Measure out a 30-inch radius around this mark.
Use the jigsaw to follow and cut the circumference line to create the top of the picnic table. Use the tape measure to measure out 20 inches out on the planks from the center 54-inch 2-by-4. Now take two of the 40-inch 2-by-4s, and secure them across the planks with the screwdriver to help support the legs.
Drill a hole through the center of each of the remaining 2-by-4s. Use the saw to cut off the ends of each of these at a 45-degree angle.
Set up the 2-by-4s in two X shapes with their holes lined up. Take the last 2-by-4 and secure it to the X with the bolts as a center brace.
Place the tabletop upside down on the ground. Place an X leg at each of the 40-inch 2-by-4s secured to the table. Screw the legs to these braces, then flip the round picnic table on its legs once you are sure they are secured.