If I loft the two generation curves, then dupedge, and use these as the rails (with handle curves closed on both ends) it works. Would love it if I knew why I had to do that extra step – which changed the curves anyway (without ‘do not simplify’ checked’; but the precision doesn’t matter at this point…)

1. When making the two cross-section curves with ‘control point curve’, how are you keeping the curves touching the ends of the ‘generation curves’? The only way I know how is to make two separate curves for each side, then join them…is there a better way? I tried ‘curve – interpolate points’, but it doesn’t stay on the generation curve ends with any editing; curve by handles is awkward but workable…any suggestions?

2. After making 4 cross-section curves and joining the pairs, when I try ’sweep 2′, picking the two rails, then two joined cross-section curve pairs, I get ‘Sweep2 failed to make a surface’. Is this because each cross-section curve is actually two joined curves? When I try single curves (not joined, from ‘handles’) for the cross-section curves, I also get ’sweep2 failed to make a surface’; when I try only choosing one of the cross-sections, I get the same thing. Flipping which curves are ‘rail’ and ‘cross-section’ make a surface, but not the one we want…and drawing un-joined pairs fails with ‘Unable to sweep – Two shapes are too close together’…any advice?