After the first end has been bent to the required radius, the other should be bent by holding it in the manner shown in Fig. 28, because the joint of the tongs will prevent its being struck out of them while the blow is being delivered. When both ends have been bent to the proper radius, the ring should be finished as described in the ring exercise (page 74), where upright blows are used with a leverage effect.
=50. The backing-up blows= are used to upset metal when it is impossible to upset it in the usual manner, and in backing up the heel of a scarf.
[Illustration: FIG. 29.—THE BACKING-UP BLOW, FOR UPSETTING.]
Upsetting with backing-up blows is done in the manner shown in Fig. 29. The metal should be extended over the anvil and thrust forward as the blow is being delivered, to get the best results. This will also prevent jarring the hand. The metal should be as hot as possible when being upset in this manner.
The heel of a scarf is formed with backing-up blows after the metal has been upset in the usual manner. The blows should be directed so that they will have an upsetting effect, as indicated in Fig. 30, and not a drawing one. After a few blows have been delivered with the face of the hammer, they should then be delivered with the ball to form the heel better and more rapidly.
[Illustration: FIG. 30.—BACKING-UP BLOWS USED FOR SCARFING.]
=51. The shearing blow= (see Fig. 31) is conveniently used for cutting off small portions of metal instead of employing the hardy. It is delivered so that the side or edge of the hammer will pass by and nearly against the side or edge of the anvil. A blow so delivered will have a shearing effect and cut the metal. It is perfectly proper to use this blow for its intended purpose, but it should not be used when the edge-to-edge blow is the one really required.
=52. Forging.=—Forging is the operation of hammering or compressing metals into a desired shape. Seven specific operations are used. Sometimes a piece of work or forging requires two, three, or even all of them to complete it. These operations are designated by the following names: drawing, bending, upsetting, forming, straightening, twisting, and welding.
[Illustration: FIG. 31.—THE SHEARING BLOW.]