It’s a bit fuzzy but I think these guys were making window frames rather than food grade materials. I do know that for certain impurities in metal recycling, t

It’s a bit fuzzy but I think these guys were making window frames rather than food grade materials. I do know that for certain impurities in metal recycling, they have a tendency to accumulate at the top or bottom of the billet, so cutting off those sides to make the billet square removes a lot of sins. But some documentaries don’t show this step, and some the billet doesn’t appear to have been modified before subsequent use. It’s possible that there are steps we aren’t shown/skipped as either trade secrets or too complex to explain.