Over the years I have built several different versions. The earlier versions were "no name" designs copied from some existing chairs that I ran across. Then I built a "Jake's Chair", but found it to be too wide and not very comfortable. The most recent ones that I have built are a modification of "Norm's Chair". I've found his design to be the most comfortable so far. The first ones were made exactly to his design, but they developed several problems in use. I've added a cross brace between the rear legs just below the chair back To stiffen and strengthen the rear legs. I also doubled the thickness of the curved back support between the rear of the arms. I did this because Norm's original design did not provide much material to attach the back boards and they would quickly loosen in use. The back boards need more than the one screw per board attachment at this point and the angle of the joint prevents using screws of the needed length. Construction adhesive along with the screws, bolts, and these modifications makes "Norm's Chair" very solid and long lasting. I've made some of the early chairs from pine and painted them, then some from treated lumber and also painted them, and then some from cypress and left them unfinished. Cypress is by far the best choice for long life and low maintenance.
Charley