Hi Tim..
Been following this project since i first saw the turrets on the other forum. Sadly i couldn't comment over there as i'm not a subscriber.....but by happenstance came across you on this forum...so all good. Great work so far. You have probably forgotten more about engineering than i will ever know... Two things.... could you get a milling cutter ground to machine the node cut outs two at a time (back to back) instead of a grinding jig?.. Also, have you had a look at continuous guttering forming. These guys have a machine that they carry on the back of a van and form guttering out of aluminium from a roll. Obviously the machine would be unsuitable...but perhaps the process might bear thinking about?... Anyway, enough of me blabbering on about things i plainly know nothing about...Keep Safe