Bending bars are a tool that I learned of in Simon Bolton’s excellent Scratch-Building Model Railway Locomotives. It is one of those things that I suspect most UK modelers take for granted but are not widely known on this side of the pond. The concept is simple: a pair of precisely matching steel bars joined by hex bolts at each end that you can clamp a sheet of metal between. Obviously, you can then make a straight bend in the metal. (Bare brass sheet for illustration purposes, one normally marks out a line using marking die or such)
Bending is not the big thing as far as I am concerned. Simon details a method of making straight breaks by repeatedly bending back and forth on the fold line which is first scored with a utility knife. This is very close to the styrene score and snap method I have used for years. And it works remarkably well! Much better than my initial efforts at soldering large pieces of brass, for instance. The resulting pieces are straight and the edges requires only a little draw filing. Both those techniques are described by Simon in videos on his Youtube channel.
As far as sourcing bending bars, I was unable to discover a supplier in North America so I ordered a set from Vince Gibson. I am certain that there are other suppliers as well. One could also fabricate a set from scratch if suitable bar stock can be obtained especially if price is a factor.