Photo 3- Begin chiseling the mortises by making angled cuts from the scribed lines. This establishes the perimeter of the mortise, giving you an easy reference edge to work to as you complete the mortise.

Use a square to mark out the top and bottom of each mortise as in photo 2. Sharpen your chisels, and first use them to establish the rectangular opening at the top of the mortise. Place the chisel on the marked line at the mortise top or bottom as in photo 3. Angle the chisel toward the center of the mortise for these initial cuts. Make similar cuts along the sides as in photo 4, aligning the cuts with the two edges of the holes as shown. Next make directly vertical cuts with your chisels as in photo 5, working your way inside out toward the rectangular opening you made previously. Use the walls of the bored holes as references to be sure that your cuts are vertical. Do not cut beyond the walls of these holes. Leave the mortises slightly small for now, and make them larger as needed later when you have the tenons at hand to fit the two together well.

Photo 4- Establishing the sides of the mortise.

Photo 5- Once the mortise perimeter is established, make vertical cuts to clear out the mortise, working toward the perimeter.