Bolts are made in such immense numbers, that a variety of machinery exists for producing small bolts by compression of the iron while hot into dies. But the machinery is not yet adapted to forge good bolts of large size, such as are daily required for general engine-making. Good bolts of large diameters can now be made by steam-hammers at a quick rate; and small bolts of good quality are made in an economical and expeditious manner by means of instruments named bolt-headers. There is a variety of these tools in use, and some are valuable to small manufacturers because of being easily made, and incurring but little expense. The use of a bolt-header consists in upsetting a portion of a straight piece of iron to form the bolt-head, instead of drawing down or reducing a larger piece to form the bolt-stem, which is a much longer process; consequently, the bolt-header is valuable in proportion to its capability of upsetting bolt-heads of various sizes for bolts of different diameters and lengths.

The simplest kind of heading-tool is held upon the anvil by the left hand of the smith, while the piece to be formed into a head is hammered into a recess in the tool, the shape of the intended head. Three or four recesses may be drilled into the same tool, to admit three or four sizes of bolt-heads. Such a tool is represented by Fig. 86 ; and is made either entirely of steel, or with a steel face, in which are bored the recesses of different shapes and sizes.

The pieces of iron to be formed into bolts are named bolt-pieces. "When these pieces are of small diameter or thickness, they are cut to a proper length while cold by means of a concave anvil-chisel and stop, shown by Fig. 87, or by a large shearing-machine, if one be on the premises. One end of each piece is then slightly tapered while cold by the hand-hammer or a top-tool. This short bevel or taper portion allows the bolt to be driven in and out of the heading-tool several times without making sufficient ragged edge to stop the bolt in the hole while being driven out. Those ends that are not bevelled are then heated to about welding heat, and upset upon the anvil or upon a cast-iron block, on, or level with the ground. This upsetting is continued until the smaller parts or stems will remain at a proper distance through the tool; after which, each head is shaped by being hammered into the recess. During the shaping process, the stem of the bolt protrudes through the square hole in the anvil, as indicated by the Figure (86).

This method is the cheapest that can be adopted by a maker of small numbers of bolts, because no expensive machinery is necessary. Bolts with conical heads, represented by Fig. 6, when of small size, are easily made by means of the heading-tool just referred to. The recesses in the tool are carefully and smoothly bored to the depths and diameters of the bolt-heads. And if a stop is to be forged solid with the bolt-head, such as Fig. 6 indicates, a straight groove is filed into one side of the recess with a small round file, the shape of the groove being the shape of the intended stop. This method of forging a stop in one piece with the bolt-head is very simple; the stop being formed by the same hammering and at the same time as the head itself. For several kinds of work such conical heads do not require to be fitted by being turned in a lathe ; in such cases a large amount of time is economised that would be occupied in fitting separate stops to the heads.

But when a large number of small bolts are required in a short time, a larger kind of heading-tool is made use of, which is named bolt-header. One of these, indicated by Fig. 89, is a jointed bolt-header. Another, of simpler character, is shown by Fig. 90. The actual height of these headers depends upon the length of bolts to be made, because the pieces of which the bolts are formed are cut of a suitable length to make the bolts the proper length after the heads are upset; consequently, bolt-headers are made two or three feet in height, that they may be generally useful.

The header represented by Fig. 89 contains a movable block B, upon which rests one end of a bolt-piece to be upset; it is therefore necessary to raise or lower the block to suit various lengths of bolts. In the header shown by Fig. 90 the movable block is not needed; the bolt-pieces being supported by various lengths of iron, differing in length according to the different lengths of the intended bolts. The pieces that are below the bolt are prop-pieces; two or three of them are sometimes necessary to maintain the bolt-pieces at the exact height. In the top of the header is a circular steel die, D, through the opening in which the bolt-piece is put, in order to be upset. The dies are of various sizes, and each die is tightly fixed into a die-block. The outside of every block, being of the same size and shape, each one fits the opening in the top of the header, which may be six-sided or circular. All the die-blocks are taper, to admit of being easily placed in or taken out of the header. The dies are smoothly bored, and the upper edges of the holes are carefully curved previous to hardening. This smooth curve prevents the die cutting the iron while being driven down to form the bolt-head. In the figure the bolt is shown on the die after the head is upset. Under the head are dots to indicate the bolt-stem and the prop-pieces below, which maintain the bolt-pieces at the height desired; consequently, if the pieces were previously cut to a suitable length, the bolts when forged are of correct length, and their heads of the proper thickness.

After the head is upset, the bolt is driven out of the die. This is effected by the hammerman striking the short lever L, at the bottom of the apparatus. The outside end of this lever being struck by the sledge-hammer, the inside end is raised, and the prop-pieces also, which drive out the bolt, while the smith holds the bolt-head with the tongs. To prevent the die-block being driven out at the same time, a key is fitted across the side of the block, pointed out in the figure by K. But in the jointed bolt-header two half-dies are used, which are opened sideways by a treadle, to allow the bolt to be taken out, instead of being driven out by a sledge-hammer.