Welding faults. Lack of penetration is usually caused by too low a power setting or too high a gun movement speed. Over penetration is vice versa. Contamination usually results in pores in the bead, and sometimes it merely causes spitting. In either case, the joint will be weakened. Burning through is a more extreme consequence of the factors which lead to over penetration — too high a power setting or, more commonly, thinned steel or too slow gun movement.
The corner joint can be welded from either the inside or the outside. If a folded lip is incorporated, then both inside and outside can be welded if desired, where extra rigidity is
required.
Different types of joint. Practice them all using scrap sheet steel before welding on your own car! The corner joint is made easier if one edge can have a folded lip.
