The two principal operations performed by a blacksmith are scarfing and welding. The process of scarfing consists of flattening the edges of two pieces of iron preparatory to welding, so that when the edges overlap they are of the same thickness at the junction of the two pieces as the rest of the iron. Care should be exercised in performing this operation, as the class of weld depends almost entirely upon the nature of the scarf. Scarfing is not, however, necessarily preparatory to all welding. For instance, in the butt weld, the two pieces to be welded are simply abutted together, sometimes in the fire.
The process of welding, as already stated, consists in joining two pieces of wrought metal at a white heat. The metal pieces at this temperature are in a plastic or semifused condition and when placed together and properly hammered readily unite, causing a solid body or joint. It is necessary to take the metals from the fire at just the proper time. If removed too early, the pieces cannot be successfully welded, and if left in the fire too long, the metal will be burned and rendered useless for service. Great care should be exercised in heating both pieces evenly and to the same temperature.
Unless the iron or steel is properly heated a scale will form which prevents the uniting of the two pieces. This scale or oxide melts at a lower temperature than the iron, and as a result the weld will be good if the proper heat has been secured. When using soft steel or Norway iron, the scale melts at a higher temperature than the welding heat and to overcome this difficulty, it is necessary to use a flux to soften or melt the scale.
Fluxing is the application of some good welding preparation to the joint. A good, clean beach sand serves the purpose, as it melts and combines with the scale, causing it to liquefy, in which form it is easily forced from between the pieces to be welded. For welding tool steel to iron or soft steel, the flux consists of borax and sand.