how do you shrink metal?

Western Electric 16A update....

wow... pretty vertical pieces.... ahhh.... but... but... 

I have to be honest here... although I knew the 16a would be a formidable project, I was a little aloof and dismissed most of the work as just requiring labor as it was simple sheet metal, right?  wrong.  The initial impression from walking up to a 16a is that it is finished very simply and crudely.. and in many ways, it is.. but.. but... the more we looked, the more we realized it was very accurate.. very accurate... very smooth flares...

but we also noted a differing level of finish on the several examples we have seen up close... so we thought maybe the plans were just shipped around to regional metal shops.. but now, having tried to make some of these parts ourselves, we are convinced that at least the horizontal pieces were stamped... under very high pressures... there is no other way to get the flare that smooth...

so those of you who want to follow along in the geekery, here is an example of a section:

see that upturned lip of just under an inch running the length of each side?  yes.  that one... well, if the panel were flat, you could just take it to a sheet metal break and bend it.  but because this piece is helical, the lip must stretch on convex turns and SHRINK on concave turns!  how the heck do you shrink metal?  yes, I know stretchers and shrinkers exist.  But they are crude.  inexact.  there is no way to get this level of accuracy, much less repeatability, with a shrinker.  You have to use brute force over a die.  so in the name of doing this thing properly... so that every one will be the same... and so that each will flare smoothly... we are making dies... old school.. the proper way to build this...

but until we finish that, here are some pretty vertical pieces...