The narrow edge permits the bar to touch the surfaces close to their intersection. The wide edge is better for finished fillets. Butt joints are much weaker and should be avoided when there is the possibility of the joint being stressed during use. The joint may be tacked at intervals to prevent joint movement during welding. In all cases, it is advisable to minimize heat input to the joint because of the possibility of recrystallization of adjacent areas, which will weaken the joint.
Resistance welding can provide sound welds with the least heat input compared to gas or arc welding.
Lap joints may also be used, with a fillet weld generally being made on both sides of the sheets. Resistance welding, using either spot welds or seam welding, is always done on lap or flanged joints. The thickness of the sheet dictates the minimum overlap of the joint, and is given in the schedule shown in Table 1 . Surface Preparation Joint areas must be thoroughly cleaned and abraded. Cleaning methods include grinding, machining, buffing, and abrading with an emery board or sandpaper.