These are indicated by Fig. 40, and are dovetailed in the gap of Fig. 38. After these liners are worn too thin, or the openings too wide, a new steel liner is put into the rod, without interfering with its gap.

Forging a small liner of this class requires two principal tools - a bottom fuller, to place in the anvil for shaping the inside, and a top-tool for shaping the outside of the liner while it is supported by the bottom fuller in the anvil.

The only part of such a liner which is subject to wear, is the curved or half-round portion, consequently this should be the thickest. If the liner is not required to have sharp corners at the entrance to the gap, the forging of it is performed with a bar of flat steel which is the thickness of the thickest part of the intended liner.

After this bar is reduced on both sides of the thickest part of the intended liner, one of the two outside arms is bent, by heating to a bright yellow heat, and placing the end into a slot in the heavy block, or by placing the end a proper distance beyond the anvil edge, and driving down the projecting end with a hammer, while another much heavier hammer is held on the part that remains on the anvil. When one arm is thus produced, the entire work is cut from the bar; the piece cut off being of sufficient length for the entire liner. To ascertain the length necessary, the lengths of the parallel sides of the gap are added to the length of the semicircumference which constitutes the bottom, or, as it may be termed, the top, of the gap. These lengths, added to the length of the other arm, denote the length of bar necessary

After the piece is cut off, the length of the gap boundary is properly marked upon the work to indicate the commencement of the other arm. Marking the place for bending is performed by a centre-punch, having a broad conical end instead of a narrow one. A punch with a broad end will make a hole that can be seen, without making it too deep, which would injure the work. The situation of the mark also is of consequence. When a large hole is made in a careless manner with a sharp punch, into the side of a thin bar, and the bar is bent where that deep cavity is situated, the cavity becomes a long rent, of dimensions too great to be obliterated without spoiling the work; but if the cavity is made into an edge, or both edges of the bar, and with a blunt punch instead of a sharp one, the work when bent will not be disfigured, and, if necessary, the dot or cavity can be easily erased.

After two dots are thus made into the two edges of the work, the other arm is produced from the same side of the bar as at the first bending. The two arms will then be extended from the same side of the bar, and parallel to each other.

The gap-curve is next formed by placing the work upon a bottom fuller, which is of a suitable height to prevent the work touching the anvil, and of sufficient thickness to form the gap desired. At the first heating for this curve, the liner is placed upon the fuller with the two arms of the work upwards, and while the fuller is precisely midway between the two arms, a broad half-round top-tool is employed to force down the gap sides; and when the top-tool will not force the metal further without thinning the top of the work, a smaller top-tool is applied, and the curving is completed by hammering, and also stretching, to lengthen the gap to the proper dimensions.

Another method of making these liners consists in forging them from a bar of steel which is three or four times the thickness of the intended work. A boss is formed upon one side of the bar by driving in a fuller at two places, the boss being between. Two small or thin ends are then made, which extend from both sides of the boss to a short distance. A hole is next punched into the boss with a punch of elliptic section ; or, as a substitute, an ordinary circular punch. The hole is made at a short distance from the edge of the work; after which, the thin piece is cut out by a chisel, and the gap is thus partly formed. The gap-sides are next lengthened by hammering, while on a narrow bottom fuller, on the anvil, and also while on a fuller having a long handle, which is held by the smith. Lengthening the gap is also performed by driving a top fuller into the gap while it is in a half-round bottom-tool in the anvil.

By this method, all upsetting, to produce what are named square corners, is avoided. As soon as the hole is punched, and the thin piece adjoining cut out with a chisel, the angular corners or entrances to the gaps are produced, and so continue till the forging is complete.

Stud Rivets

These are occasionally used for beams or other work when it is necessary to penetrate entirely through and effect a fastening at the other side. The shortest method of forging one, which is denoted by Fig. 39, consists in making a collar or flange, and welding it to the stud, at a proper distance from the extremity. Such studs must be made of soft iron, for the convenience of riveting ; and if it is necessary to frequently fix or unfix them, a screw and nut are used instead of a rivet.