My hat goes off to Leonard for recommending the triangulated block method for jigging. It is just so secure. Setting the rib onto the rear spar shows the exact cut line required to get the chamfer correct so I marked with a pen and then along the rear face of the spar. The black texta mark on the top is a guide to not plane through when using the electric plane. To the edge is fine but definitely not through. Gently, gently did it with the electric plane after which I was able to pass the rib completely through from one end to the other. Same on the next rear spar and the mark and plane method was used on the main spars.