Dig a hole with your post hole diggers. Stab the blades of the tool into the ground repeatedly to break up the dirt. Stab into the ground and pull the handles of the tool apart to pick up dirt. Remove the dirt and continue digging. Make the hole 30 inches deep and 12 inches wide.
Measure 7 feet from the first hole with your tape measure and dig a second. Dig a third hole 18 inches from the first and a fourth hole 18 inches from the second. Place the third and fourth holes 7 feet from each other so that all four holes form a rectangle.
Shovel 6 inches of gravel into the holes. Place a 4-by-4 inch post into each hole and pour in Portland cement. Push the posts from side to side, forward and backward while checking the plumb of each post with the 4-foot level. Be sure each post is standing perfectly erect. Add three quarters of the amount of water recommended on the bag. Allow the cement 24 hours to dry.
Measure along your drill bit starting at the tip. Wrap electric tape around the drill bit at a point 3 inches from the tip of the bit. Drill into the top of each post until the bottom of the tape is even with the top of the post, giving you a 3 -inch hole in each post. Pour epoxy into the holes in your posts and insert a 4-inch piece of all thread. Allow the epoxy 1 hour to cure.
Measure your bit and mark it with a piece of tape at a point 1 inch from the tip of the bit. Stretch your tape measure along the length of your handrail. Make a pencil mark in the center of the handrail at a point 18 inches from each end of the rail. Repeat the marks on your other handrail. Drill these spots to 1 inch deep by using the electric tape on your bit as a gauge.
Fill the holes in your handrails with epoxy and flip the rails over so that the all thread in the posts slides into the epoxy-filled holes in the rails. Allow 24 hours curing time for the epoxy to harden and bind the rails with the posts.