To sharpen the 2x4s into points, draw a V-shape on the end of the boards (Image 1). Use a circular saw to make the cuts. You only need to sharpen one end of each board. Set these aside and then cut the two remaining boards down to 6' in length. Cut both of the remaining 2' long sections of 2x4 in half so you have four boards 1' in length (Image 2). These pieces will form two trellises that will sit back to back in your planting bed. The short pieces will hold the two frames together to make them sturdier. The first step is to get the pointed boards into the ground. Hammer all of the pointed boards evenly along your bed, so that all boards are the same depth and height (Image 3).
Using a drill and 3" galvanized screws, attach one 6' long board across the top of each pair of supports. You want to use galvanized screws to prevent rusting; you could also use stainless steel screws (Image 1). Then screw the short boards to the outside of the frames at the top and near the middle to connect the trellises together. The short boards will make the two trellises sturdier and they'll maintain the distance between the two sides (Image 2). That way if you get any heavy wind they'll stay in place. Once these are covered in vines the trellis will act like a big sail in heavy weather. That's why it's so important to make them secure.
The center of the trellis will consist of various string supports attached to nails. To build the string supports, begin nailing 1-1/2" galvanized flathead nails to the inside of the boards. Space them about 10" apart. Leave about 1/4" of the nail sticking out, leaving space behind the head to attach the string (Image 1). Use a ball of garden twine to create the netting on the trellis (Image 2). You can also use fishing line or plastic garden fencing to face your trellis. Begin at the bottom nail and tie off one end of the string. Pull the string across to the second board and looped it around the corresponding nail. Then go directly up to the next nail, loop the string around and then pull it back to the first board. Continue looping and pulling the string until the entire span of the trellis is laced. Tie the string securely to the last nail. The final step is to install the vertical trellis strings. Start at the top by attaching the string to a nail. Drop the string straight down and tie it to a horizontal string with a single knot each time the strings cross (Image 3). At the bottom horizontal string tie off the string and then cut it off.