If the metal to be straightened is round, or if it is flat with round edges, it is best to use a top swage of the proper size and deliver the blows on the swage as shown at B, [Fig. 39]. Then the surface of the round or the edges of the flat stock will not show any marks. The flatter or round-edged set hammer may be used in the same manner on flat or square material.
Fig. 40.—Straightening Wide Metal.
When wide pieces of flat metal are to be straightened edgewise, and such blows as are shown at A, [Fig. 39], are not effective, then the blows should be delivered along the concave edge as shown in [Fig. 40], and distributed as indicated by the dotted circular lines. Blows delivered in this manner will stretch or lengthen the metal on the concave edge and straighten it.
58. Twisting is the operation of rotating metal to give it a spiral appearance. It may be done either hot or cold, as the dimensions of the material may require. It is done by holding the material in the vise, the hardy hole, or the swage block, and turning one end of it with a pair of tongs or a monkey wrench as many times as may be required. The twisting will be confined between the places where it is held with the vise, and where it is seized by the tongs or wrench.
If the material to be twisted is heavy enough to require heating, a uniform heat is necessary or the twist will be irregular, and, as an artistic appearance is usually desired, this operation should be carried out with that result in view.
Fig. 41.—A, Metal Twisted while Hot; B, Metal Twisted while Cold.
A, [Fig. 41], illustrates a piece of 1⁄2-inch square stock that has been twisted while hot. B shows a piece of 1⁄2 × 1⁄8-inch material that has been twisted cold.
Another difficulty met with in twisting a piece of metal is that of its becoming crooked. It can be straightened by laying the twisted portion on a wooden block and striking it with a wooden mallet. This will prevent the corners from becoming marred. A good method of avoiding this trouble is to twist the metal inside of a piece of pipe whose inside diameter is equal to the diameter of the metal.