The top and bottom rails on the back assembly have angled shoulders on the front that accommodate the angle of the front stile. Yet the tenons remain square to the back stile. To start, cut the rails to their overall lengths (the top rail is shorter than the bottom one). To cut the shoulders you’ll need to attach an auxiliary fence to your miter gauge as you see in Figure 1 below.
First, set the angle on the miter gauge, then mark the location of the shoulder on the edge of the rail. Use your rip fence as a stop to make the pass over the dado blade (Figure 1a). From there you can back away the board and remove the rest of the waste on the cheek. Do this on both of the rails.
After adjusting the miter gauge, you can make the shoulders on the opposite face of the rails, as shown in Figure 2 below.
To trim the tenon to it’s final size, bring the miter gauge back to 90°. Then tilt the blade 5° and make the shoulder cut as shown in Figure 3 below.
Back at the bench you can remove the remaining waste with a backsaw (Figure 4 below).
You won’t have any problem making the tenons on the other end of the rails. Figure 5 below shows you what to do.
