Dear rollupswx,
This note may appear out of turn but it is just to thank you and to add that I accept your kind advice over keeping original sketches simple, which is why I had driven my sketch from circles rather than from individual lines requiring many measurements and angles. In subsequent models I have set up layers of sketches each building on each other using blocks that appears to work well, keeping each individual sketch confined to just a few construction lines constrained to the underlying blocks.
In summary, the very meaningful help I received from you last night was:
1. The missing 2 dimensions from my sketches related to not being constrained to the centre of origin.
2. When Inventor fails to corner mitre overlapping flanges, simply use an offset and fix the problem with a separate corner seam.
3. That there is possibly a much better route to folding up from a flat namely to loft.
Finally there is no doubt that without your kind help I would have been stuck on this problem for a goodly while.
So thank you rollupswx, you get my sincere vote of thanks.
cjj