I think I didn't give dirtdorphins the right specs last night - so I created a drawing of the arch. It's not to scale at all, but the measurements in it are on for what it is.
It was flat when I put it together (welded it on the driveway) and we made the curve when we put it in the garden. I made the curved piece first, then attached the sides/rungs.
Do with it what you will. I'm sure you can modify it for your needs...or a semi-clever welder could put something similar together just with the drawing and this description.
The neatest thing, like Dirt said, is how it looks from different angles. That curve and varied outside rung length really do something tricky with shapes.
