These are indicated by Fig. 16, and are forged by two methods. One mode consists in marking the lengths required for the rings along a bar of iron or steel, and piercing the bar midway between every two marks that denote the amount of iron required for one ring. The openings are made by circular punches, or by circular punches which are both circular and elliptical. Above the elliptical portion the punch gradually increases in diameter, and the shape becomes circular; consequently, it is a circulo-elliptic punch. This kind of punch cuts out but a small piece of metal, and at the same time makes a comparatively large hole, the precise diameter of which depends upon the amount of the punch that is driven through the iron.

The circular form for the outside circumference of the ring is partly developed by cutting off the corners while the ring is still attached to the bar; after being thus trimmed with a chisel, the ring is cut from the bar and shaped while on a mandril. Each ring is heated to welding, and the rounding is performed with top and bottom tools. If it is necessary to enlarge the opening, a taper mandril is used, and the ring is drawn or stretched by hammering the edge of it while tight on the mandril. During this stretching, the mandril and ring are rotated by the smith to produce an equal thickness throughout.

The economical mode of making large rings consists in forming them from a straight bar which is of a suitable width and thickness. The bar is cut into pieces, each being of the length required for one ring. The pieces are thickened at each end, scarfed on opposite sides, then bent to a circular form, and the scarfs welded together.

Previous to cutting off the pieces, the bar is reduced to that thickness which will allow not more than sufficient iron for boring and turning the rings to their finished width and thickness. If the opening of the ring is to be bored in a lathe to 5f inches diameter, and the thickness of the ring's face-side to be 5/8 of an inch when finished, the forged thickness of the ring should not exceed 7/8 of an inch; and this is the thickness to which the bar is to be reduced previous to cutting off the piece or pieces.

If the bar is reduced to the required thickness, the length of each piece should equal the length of the middle circumference of the ring's face. The face-side of a ring is the side which is placed next to the plummer-block cap, or to the connecting-rod cap; and if the required forged thickness of the ring is 7/8, and the required diameter of the opening or hole when forged 5 1/2 inches, the outer diameter is 71/4 inches. The length of the mid-circumference is therefore 20 inches, because its diameter is 63/8 inches. The length of bar required for one ring is consequently 20 inches: nothing being allowed for scarfing, because, during the scarfing, nothing is cut off, the scarf being drawn by a fuller while the piece is straight. After 20 inches of the bar 7/8 thick is scarfed, formed to a circle, welded and flattened; the diameter of the opening is 51/2 inches, and the outer diameter is 71/4 inches; which will allow rather more metal than an ordinary turner requires, to produce a ring 5/8 thick, and whose opening is to be finished to 53/4 inches as desired.

The precise amount required for boring and turning depends upon the smoothness or roughness of the work; and also upon its form being, or not being, nearly circular. This is attained by rectifying each ring after measuring it with callipers, both inside and outside. After discovering by the callipers which is the longest diameter of the ring's opening, it is rectified by placing the ring upon the anvil with the longest diameter vertical, and striking it by hammer and top-tool.

It is always advantageous to make the bar or piece the proper thickness previous to making the ring; although it is not absolutely necessary, because the ring may be stretched by hammering, after being welded. Previous to welding, the piece may be thicker than the finished forged thickness, but not in any case thinner. Whatever may be the precise thickness of the bar previous to making the rings, the author's rule here given is always applicable :

As the thickness of the bar from which the ring is to be made is to the required forged thickness of the ring, so is the length of the middle circumference of the ring's face-side to the length of bar required for the ring.

The length of the middle circumference is discovered by referring to ordinary tables, or by multiplying the diameter by 3.1416. The diameter of the opening of the ring when forged being 5 1/2 inches, and the forged thickness to be 7/8; the outer diameter must be 71/4, and the mean between 51/2 and 7 1/4 must be 63/8, which is the diameter of the middle circumference required. Multiplying 6f by 3.1416 produces 20 and a fraction, too small for us to notice in this case, consequently 20 inches of bar is sufficient to make one ring, if the bar is 7/8 thick.

But if it should be necessary to use iron which is an inch thick, a shorter length of bar would be sufficient. This is demonstrated by applying the rule and making a ring of a piece of bar which is the length indicated. For example :

1 : .875 :: 20.02 : 17.52; the first term denoting the thickness in inches of bar used, the second indicating the required forged thickness of the ring desired, the third term representing the length of its mid-circumference, and the fourth term pointing to the length of inch bar required. This length is 21/2 inches shorter than the proper length of bar, which is 7/8 thick. If bar 7/8 thick is used,' the complete proposition is thus represented :

.875 : .875 :: 20.02 : 20.02; twenty inches of 7/8 bar being used will obviate the necessity of drawing or stretching the ring, either before or after being welded together.

French symbols of dimensions also are given, because of their great utility and simplicity. Seven-eighths of an inch equals 22.2 millimetres, and 20 inches equal 508 millimetres, consequently the proposition appears thus: