Large wooden gates, due to their size and weight, have a tendency to warp or sag over time unless they are properly braced and supported. Constructing a 6-foot-square gate is a simple project. Like any other wooden gate, it has two essential components: the frame and infill material. Due to its size, additional bracing is needed to prevent the large frame from warping. In addition to a long wooden diagonal brace, smaller steel diagonal braces reinforce each corner. No special tools or advanced carpentry skills are needed for this project.
Sketch your plans for the finished gate; include dimensions for the rails, stiles, and infill material. The rails and stiles are each 6 feet long. Infill material is also 6 feet long. Set the chop saw to make 45-degree cuts. The ends of two rails and two stiles will be cut at 45 degrees in divergent angles (not parallel) to form the mitred corner joints of the frame.
Trim the end of one 2-by-4-inch plank at 45 degrees by placing the plank with its 4-inch surfaces horizontal and holding it firmly against the guide fence of the saw before making the cut. Measure and mark the longest side of the cut plank to 6 feet. Reposition the plank on the saw table and cut the opposite end. Since the rails and stiles are all the same length, cut three more planks to the same length to form your gate frame.
Assemble the frame on a flat surface, like a picture frame. The corners should form perpendicular mitred joints. Attach steel corner braces to the outside corners of the frame, centred to the thickness of the planks. With a drill, driving bit and 1 1/2-inch wood screws, affix the steel braces to the corners of the frame. The corner braces will stabilise the joints, but they will be somewhat movable until the diagonal steel braces are attached.
Mark the gate frame to indicate top and bottom rails, and hinge and open-side stiles. Position a 1-by-4-inch plank diagonally across the frame from the lower hinge-side corner to the upper open-side corner, crossing the rails at either end. Use a carpenter's square to check each corner of the frame for squareness. Adjust positions of the framing members, if necessary. Once you are satisfied that the frame is square, use the straightedge of the carpenter's square and a pencil to scribe cutting lines on the ends of the brace where the plank meets the outside edges of the rails.
Remove the plank. Cut the brace on the lines. Reposition the brace on the frame. Recheck the corners of the frame to ensure they are still square. Attach the ends of the brace to the rails using four evenly-spaced 2-inch screws, a drill and driving bit. Position steel mending plates diagonally across the two unbraced corners of the frame. Attach the mending plates to the rails and stiles using 1 1/2-inch screws to form triangular braces. Turn the frame over.
Position the first and last infill planks on the frame, aligned to the stiles and rails. Screw the planks to the rails with two evenly spaced screws in each end of the plank. Screw the outer edges of the planks to the centres of the stiles. Space the screws approximately 6 inches apart. Attaching the outer infill planks to the rails will help to strengthen the gate.
Arrange the remaining infill planks between the outer planks so they are parallel and evenly spaced. Attach each plank with two screws, evenly spaced, to the vertical centre of each rail. The finished gate is ready for installation.
To prevent an especially heavy gate from sagging, one-third on the overall length of the gate post should be underground. Using three hinges and a gate wheel distributes the weight of the gate over a larger area, further preventing sagging.