The welding of two pieces of stock by scarfing and lapping is known as a separate-heat-weld, so called because the pieces are detached while the heat is taken. In making any kind of a weld there is more or less stock wasted in the raising of the welding heat, therefore the parts to be lapped and welded are always upset or thickened and then scarfed. The word “scarfed” means the shaping of the ends of the bars so that when heated and lapped one on top of the other, they will fit and make a splice, leaving the stock when hammered about its original size.
The method of upsetting is to heat the ends of the bar, then set the hot end on the anvil with the bar vertical and hammer on the other end. This thickens the heated end. If it is a long heavy bar, the worker churns the bar up and down striking the hot end on the anvil. A bar may also be heated on the end, then fastened in a vise and the hot part hammered to thicken it. In upsetting, the bar must be kept straight as hammering will bend it where heated; if not kept straight, it will not thicken.
Fig. 22. Fig. 23.
When a piece is upset about one inch in diameter for a three-quarter inch, round bar, it is scarfed by setting the hot end on and near the outer edge of the anvil. It is then driven back on a bevel by hammering. See [Figure 22]. It is also turned on the side and beveled on both sides to nearly a point. See [Figure 23]. The scarf must not be hammered when the piece is held in the center of the anvil, ([Figure 24]), for the reason that the edge of the hammer comes in contact with the anvil, pecking dents in it or breaking out pieces from the hammer.
Fig. 24. Fig. 25.
Another method of scarfing is to hammer the end partly back as previously explained, then set the piece on the inner edge of the anvil and hammer it as shown in [Figure 25]. After each blow, it is drawn away from the edge of the anvil just a little; this tapers it with a series of little steps, not for the purpose of making notches in the scarfs to fit together and hold while hammering, but simply because the edge of the anvil leaves it in this condition when tapered. It is also drawn pointed by hammering on the outer edge of the anvil.
Theory teaches that the scarf should be made with the beveled part convexed. However, in practice, it is made to look like the drawing in [Figure 26]. Note the raised parts at “D”. This is forced up when the scarf is first driven back with the hammer as shown at “B”.