The base upon which the swage block rests is constructed with lugs on the inner side, as indicated by the broken lines on the sketch. Upon these it is supported, either flat or on any of its four edges. These lugs prevent the swage block from tipping sidewise.
30. The surface plate (C, [Fig. 16]) is generally made of cast iron about 11⁄2 to 2 inches thick, from 20 to 24 inches wide, and from 3 to 4 feet long. It should be planed perfectly smooth and straight on its face, the edges slightly round. It should be supported on a strong wooden bench D and placed somewhere in the middle of the shop so that it is accessible to all the workmen. On it work is tested to see whether it is straight, perpendicular, or if projections are parallel. The anvil is sometimes used for this purpose, but as it is subjected to such severe use, the face becomes untrue and therefore cannot be depended upon. A true surface plate is always reliable and convenient for testing work.
Fig. 16.—The Surface Plate.
31. The tapered mandrels ([Fig. 17]) are made of cast iron, and are used for truing rings, hoops, bands, or anything that is supposed to have a perfectly circular form. The height ranges from 21⁄2 to 5 feet; the largest diameter varies from 8 to 18 inches. They are cone-shaped with a smooth surface, and should be used with caution. The blows should be delivered on the metal where it does not come in contact with the mandrel; when bands of flat material are to be trued, the best method is to place them on the mandrel from each side alternately. Unless this precaution is observed, the band will be found tapered the same as the mandrel. Alternating is not so necessary when bands or rings of round material are handled.
Mandrels are sometimes made in two sections, as shown at B and C. As B is made to fit into the top of C, the two parts become continuous; the smaller one can also be held in the vise or swage block and thus used separately. They are frequently made with a groove running lengthwise, which allows work to be held with tongs and provides a recess for any eyebolt or chain that may be attached to the ring.
Fig. 17.—The Tapered Mandrels.
It should not be supposed that all mandrels are of this particular form; any shape of bar, block, or rod of iron that is used for the purpose of forming or welding a special shape is called a mandrel.