Fig. 2883.
Let the length of the two pieces be longer than the finished length to an amount equal to the diameter. Then cut out a piece as at a, in [Fig. 2882], the step measuring half the diameter of the bar as shown. The shoulder a is then thrown back with the hammer, and the piece denoted by the dotted line b is cut off, leaving the shaft as shown in [Fig. 2883].
The faces of the scarf should be somewhat rounding, so that when the weld is put together contact will take place in the centre of the lapping areas. Then, as the surfaces come together, the air and any foreign substances will be forced out, whereas, were the surfaces hollow the air and any cinder or other foreign substances would be closed in the weld, impairing its soundness.
Fig. 2884.
The lap of the two pieces, when scarfed in this manner, is shown in [Fig. 2884].
To take the welding heat the fire should be cleaned out and clear coked coal, and not gaseous coal, used. The main points in a welding heat are, to heat the iron equally all through, to obtain the proper degree of heat, and to keep the scarfed surfaces as free from oxidation, and at the same time as clean, as possible.