Lacking any CAD tools, I'd do the layout on cardboard; study and plan the
bends, order of the bends, growth of the metal, etc.
Our networking shop made a few "impossible" boxes this way back in the '80s.
We won a bet with a local old-timer sheet metal guy who claimed one box
"couldn't be made" in one piece. Got a couple-cases of beer and a nasty
look from the geezer when we bent it up on HIS finger brake. It was a
sequencing issue. He couldn't mentally get past some interfering "reverse
bends" that actually didn't get in the way if they were made in the correct
My condolances :-) Rhino 3d has some nice features in the new V4 that
can flatten out items like this, even if they are not planar. One
command called 'smash' used an icon of a roadkilled cat with a tire
tread through it. :-) Origanally designed for things like hot air
Machinery's handbook has a section on bending sheet metals. The key is
to know where the neutral plane is in the bend. I had an old edition,
back about 9 or 17 that had a really good article. The later editions
have the section, too, but it is a little harder to use.
Basically, I have used 20% from the inside of a 90 degree bend as
the neutral plane with good results.
I am not a sheet metal worker, just a guy who has to use the stuff
once in a while.