"William G Darby" wrote in message news:
my imagination was the idea of milling something like a 3/4" dia ball nosed*
end mill slot 3/8" deep along the top edge of a .5" by 3" al/steel bar about
7' long. If I then placed a half round 3/4' rod in the channel and a
clamping plate whose edge lay exactly along the center line of the rod I
would have a 7 foot "light metal" brake.
I should be able to get a perfect 7
foot 90Ebend. This arrangement seems quite sound as it provides support for
the full length of the bend and axis of the bending face is forced to rotate
exactly about the axis of the required bend and therefore there should be no
deviation from the desired bend line.

not sure if i have read this right, i think you will get a bend with a
large radius one side.
I make sheet folders when i need to, never made a neat one to keep..
if the material isn't bent down against something it doesn't bend
sharply, you will be bending it down against part of the half round
stock, which will be below the level of the back of the slot/groove?
or have i got it all arse about face....
hinged benders are easy to make.
i did put a webpage together with a simple one on.
--
richard