Figure 134 shows the method of scarfing edges to be welded and various ways of manipulating the torch and welding rod. In every case the metal must be filed or ground well back from the edge, forming a wide notch or groove into which the metal is flowed. This
ELECTRIC ARC WELDING AND ELECTRIC WELDING differ somewhat in the technique and apparatus employed. The seams of gas tanks on automobiles are often electric welded—but not arc welded. The method employed in the Ford plant is to run the seam, after it is pressed together, through the two copper rollers which form the contacts. These bring the edges of the tank metal into contact, while welding heat is generated at the point of contact, and the two pieces are made into virtually one piece.
"Spot welding" is similar, except that the two pieces of sheet metal are held between the ends of rwo coppcr rods carrying current of the right intensity to generate welding heat at point of contact.
This is a most useful process commercially, being quite Tapid, and the joints permanent. An example of its use may be found in the metal stools and chairs used at soda fountains the legs being thus "tacked" or "spotted" to the metal rim of the seat.
Arc welding may best be understood from Figure 135, which
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