Although the assembly went on to be slightly out of hand, but the hollows for the screws partially so deeply set that a tightening of the screws causes that this slip in the rod inside.
The screws are of such low quality that these places simply dissolve screwing together and to this 'hollow turns', even if you used the exact matching bit for it.
Solution to the problems is the design easy to weld together, since only the nuts and bolts (and the drilled holes) are really the problem.
