For the turnbuttons, be sure to mark these on the inside of the aprons. On the two aprons where the turnbutton is centred, measure the length of the aprons from the shoulder line, in Paul’s case this is 9 ¾“ (248mm), and take off 1 ½“ (38mm) from the overall measurement (8 ¼“ (210mm). Divide this measurement in two, in this case Pauls is 4 ⅛“ (105mm) and use this as the distance to mark up from the shoulder from both sides, this should leave you with 1 ½“ (38mm) in the middle of the apron for the turnbutton mortise.
The other two aprons have different turnbutton mortises. On one of these aprons, measure in 1 ¼“ (32mm) from the shoulder line and make a mark, then measure 1 ½” (38mm) from this and make a mark. Do the same on the other end. Repeat on the other apron.
Set your gauge to your ½“ (13mm) chisel and your stock ½” (13mm) away from the moveable pin. Run your gauge in between the turnbutton mortise lines on all four aprons
Cut these to ⅜“ (10mm) deep.