Fillet weld fusion face angle

The fillet weld flank angle determines how well you can get into the weld and how the forces will later run through the component. If the angle is too large, you get poor penetration and the weld becomes brittle because you're putting too much heat in at once. That leads to cracks or the weld tears under load. You need to set the angle so that you can get cleanly into the root with the electrode or torch, but not work too flat. For stiff components or when you have high stresses, take the angle rather smaller, then the weld holds better. And don't pile on too much material at once, but apply several layers, then the weld stays clean and pore-free.