Cut one end of each 70-inch board at a 30-degree angle. The angle should lead to a 1/8-by-1-inch tip at the end of the board.
Lay the 70-inch boards flat and at a 60-degree angle. The ends with the cuts should be aligned. The surfaces created by the cuts should be facing each other, parallel and 1 inch apart. Place the 68-inch board between the 70-inch boards so its end is flush with the ends that have the 30-degree cuts. This apex is the top of your easel.
Drill an 1/8-inch hole through the 1/2-inch center of the three boards so it is 1 inch away from the end of the apex. Insert the bolt through the hole and tighten the wing nut around it.
Place the 25-inch board on top of the three boards so it is perpendicular to the 68-inch board. The 25-inch board should be 34 inches away from the end of the 68-inch board that is opposite the end of the apex. The ends of the 25-inch board should each be 12 inches away from the sides of the 68-inch board. Drill two 3/32-inch holes through the 1/2-inch center of the 25-inch board so one hole enters the 1/2-inch center of each 70-inch board. This is a pilot hold for your screws. Screw the 25-inch board to the 70-inch boards.
Screw an eye-hook to the 12.5-inch center of the 25-inch board on the side that is facing the 68-inch board. Screw another eye-hook to the 68-inch board so that two hooks are right next to each other.
Stand the easel upright and spread the 68-inch board away from 70-inch boards until it is at a 60-degree angle. Tie the string around the eye-hooks so the easel stays in this position. Rest your canvas, picture or finished painting on the 25-inch board so it leans against the 70-inch boards.