Hi Bob, I made one of a very similar design in my last day job, most of the folding jobs there were farmed out to a shop just down the road. who had a modern heavy duty break press. The one I made was for the more occasional small folding jobs, and the one I made was 1m wide, but the holding down angle was a piece of 120 x 120 x 15mm angle, and had a piece of 60 x 12mm flat stiffing bar stich welded on the inside corner, this had the two edges of the angle milled flat to each other, and a heavy duty piece of rectangular hollow section was welded on each end for 24mm holding down bolts. The base plate was a piece 200 x 30mm flat bar, with the folding angle being 150 x 100 x 12mm, and with a couple of 100 x 50 x 6mm channels welded on in two places on the inside corner of the angle, which also acted as stiffening gussets, with a U shaped handle of 25mm bright round bar. It could fold a piece  2.5mm mild steel, but only about 1mm max., just, of 316 stainless steel. The point is the wider you go, the thicker and larger the sections need to be. I do like Alex’s idea of using a piece of flat bar for the second fold of his U shape profile.

Regards Nick.