Fixing a broken metal kitchen chair

One of the kitchen chairs broke its leg where it was welded to the seat frame. I thought that after getting the leg welded to the seat frame, I 3D-print the braces to reinforce the joints using screws and nuts. I'm using ABS plastic. Is this good idea?

What you describe sounds a good idea. I have used 3d printing to repair many things all around the house. ABS seems a good choice of plastic too as it is fairly strong and therefore likely to last longer