Fig. 2880.
Fig. 2881.
The lap weld is formed as follows: Suppose it is required to weld together the ends of two cylindrical pieces, and the first operation is to pump or upset the ends to enlarge them, as shown in [Fig. 2880], so as to allow some metal to be hammered down in making the weld without reducing the bar below its proper diameter. The next operation is to scarf the ends forming them, as shown in [Fig. 2881], and in doing this it is necessary to make the scarf face somewhat rounding, so that when put together as in the figure contact will occur at the middle, and the weld will begin there and proceed as the joint comes together under the blows towards the outside edges. This squeezes out scale or dirt, and excludes the air, it being obvious that if the scarf touched at the edges first, air would be enclosed that would have to find its escape before the interior surfaces could come together.
It is obvious, that if the two pieces require to weld up to an exact length and be left parallel in diameter when finished an allowance for waste of iron must be made; and a good method of welding under these conditions is as follows:—
Fig. 2882.