Lay two 50-inch boards on edge, so that they are parallel and 12½ inches apart. Their ends must be aligned. Position two 12½-inch boards perpendicular between them so that they are 47 inches apart. Screw through the 50-inch boards and into the ends of the 12½-inch boards. Use 12 screws for this task. You should have a 50-by-15½-inch rectangular frame.
Position a 30-inch board inside each corner of the frame so that the boards are perpendicular to the frame, and so that the ends are all flush with one side of the frame. Screw four screws through each corner of the frame and into the 30-inch boards. These are the legs of your lathe stand.
Position the stand upright so that the frame is on top. Lie the plywood on top of the frame so that all of the edges are flush with the sides of the frame. Screw the plywood to the frame using 4 screws for both 50-inch sides and 2 screws for both 15½-inch sides. Your frame is now ready to secure the lathe to.