The reason that the high part should be on the scarf, is, that when lapped it gives an additional amount of stock at this part of the laps to be hammered. If the scarfs are made flat, when hammered, they are not liable to finish up without having the pieces thin, or the point of the lap exposed. If the scarfs are made concave, it is claimed by some workers of iron that dirt will deposit there and result in a poor weld. This is true to some extent. However, dirt will deposit on any scarf unless the fire is clear. With a concaved scarf when lapped, there is not stock enough to be hammered without leaving the pieces thin, or the lapping too long when welded. Scarfs should not be made concave.
Fig. 26.
Fig. 27. Fig. 28.
Notice in [Figure 27], the incorrect way of scarfing and in [Figure 28], the correct way.
The scarfs must not be made too long; this is a common fault with all beginners and one to avoid. The scarfs should be made a little longer than the thickness of the iron, perhaps 1½ times the thickness.
In raising the welding heat, the pieces must be placed in the fire with the scarfs, or beveled part, down. The fire must be a clean one. A well burned fire is best. A new fire is not a good one to raise the welding heat in, as there is too much smoke and green coal that comes in contact with the metal. The hammer should be placed on the anvil about over the square hole, so it will be handy to reach when making the weld. The anvil should also be clean. A heavy hammer should be used in welding. The proper way to hold the hand hammer is with the fingers around the handle and the thumb protruding along the side and near the top. The thumb should never grip around the handle, but lie along the side to guide and direct the blows. When using the sledge hammer, stand in front of the anvil and not at its side, and let the first blow be a light one.
In heating a slow blast is maintained. When the pieces begin to get about yellow, more blast is used. The pieces can be watched without removing them from the fire. They should be turned over occasionally, moving them nearer to the surface of fire to see how the heat is progressing, and then under the coke again. Care must be taken to get both pieces heated alike. If one piece should get hotter than the other, it can be moved over in the fire a little, and the cool one put in its place. Perhaps the fire is hotter in one spot than another. If one piece is heating much faster than the other, lift it clear up and out of the fire for a few seconds to cool and give the other piece a chance to become hotter. If the points of the scarf are heating too fast for the body, the pieces must be pushed thru the fire a little farther.