The scarf joints of bolts, rods, and bars of two or three inches thickness can be easily welded together with steam-hammering; the only manual labour involved in the process being that of placing the two scarfs into a proper situation beneath the steam hammer, and into a bottom tool resembling either Fig. 232 or Fig. 233. One of these tools is fixed to the anvil either by means of a key at the side of the bottom tool, or by means of a square stem which constitutes part of the tool; bottom tools having square stems being employed, if the anvil contains a suitable hole to receive them.

A bottom tool for welding round iron is shown by Fig. 232, and another for welding bars is denoted by Fig. 233. In the one for round iron, the gap is wider and deeper at the middle than at either end, this form being that which is suitable for producing rods that are to be thicker at the joint; and also highly advantageous for welding, reducing, and smoothing a joint at only one hammering. The corresponding top tool has a gap of similar shape, and should be so guided to the bottom tool that when both are together the widest part of one gap shall be opposite the widest part of the other gap. For this purpose, the guide-rods may be two or four in number; the tool shown by the Figure having four. Around each guide-rod is a coiled spring to raise the top tool.

While preparing the scarfs for welding by this method, it is advisable to so shape the ends as to obtain an oblong section, making the greatest length of the oblong to be in a vertical position while the scarfs are under the hammer ready to be welded. After the scarfs are shaped and heated to welding, the two pieces are conveyed to the hammer, and put into the shaping or welding tools from opposite sides, each piece being held or guided by one or two men at opposite sides of the welding tools; consequently, the two scarfs are pushed towards each other in opposite directions, until one is on the other in the required position, at which time the man who works the hammer drives down the top tool and the welding is commenced, the springs between the two tools pushing up the top tool at each blow, to permit the work to be rotated or partly rotated when necessary.

To weld a bar joint in a tool shown by Fig. 233, the two pieces are put together in a similar manner, but no top tool is required except an ordinary flat-faced hammer, the desired shape of the joint part being obtained by making the gap in the tool of a suitable width and depth.