Joining the newel to the stringer
With the shoulder line determined we can go about marking and cutting the tenons on to the stringers and morticing the newels ready to accept the stringer tenons.
The closed stringer tenon.
The tenon position is fairly straight forward, once you have the shoulder line determined the tenon can be formed onto the end of the stringer, the only real thing to be aware of, is that the tenon is set in the solid timber and does not encrouch into the tread and riser rebates. This will avoid having a tenon with a tread rebate going through it and weakening the tenon.
Make sure the the tread side of the tenon does not cross over line A-A and into the rebate area.