The jig did not work at all well. I designed it with 2 purposes, one to prescribe the final (outside) dimensions of the bent aluminium tube and secondly to bend the tube itself. One purpose frustrated the other and vice versa. To meet the second purpose the tube had to be inside the jig on one side of the bend and outside the other side of a particular bend. With 5 bends in the design it was always going to be problematic with either 2 insides (impossible) or two outsides at a particular bend.
I should have made two jigs; one for the outside shape prescription and, one (more robust and more accurate with better clamping arrangements) to perform the bending itself. You live and learn.
I ended up repeatedly annealing the work piece and bending it between my thumbs as best I could.
I did however need to bend the "hoop" across the widest dimension (i.e. 2 bends at once) so I had to lash up a jig to achieve this.
