Next cut your tenons. To see how to do this, see ‘How to Cut a Haunched Mortise and Tenon’. Keep checking your corresponding tenon against your mortise and adapt them to suit a specific mortise hole. You will need to transfer the ¼ “ (6mm) line on the other opposite end of the tenon to the mortise and cut. Transfer the haunch onto the tenon, use the 6mm chisel to mark out the depth from the shoulders.
Mark inside your mortise with a knife as this will be the inside of a mitre where both tenons join.
Use the mitre marking as a guide to cut 45° from the corner. Cut the corner of the other tenon 45° the other direction. Progress all four aprons up to this stage.