Subdivision of Surface gone wrong (application of space frames)

Hi 

I generated a surface using arcs/loft..etc (as you can see from my code) then I subdivided that surface and evaluated its normal so that I can then construct space frames from that. Everything looks fine and is working right however when the space frames reach the end of my surface, it all goes towards one point and becomes jumbled up and I dont really understand why that's happening. I want to be able to produce a space frame that I can then use for 3d printing and I would really appreciate the help on what to do!

Thanks