Assemble the joint. It should be a sliding fit. Make sure the shoulders are even and then mark the thickness of the mortise member on the top of the tenon. Remove the tenon member and using a try square, mark a line about 3mm behind the line you have just drawn; this will become the back of the mortise for the wedge. Carry this line around the tenon. The wedge should be cut with a slope of 1-6, and its thickness should be no more than one-third the thickness of the tenon. Its length should be about three times the width of the tenon.