Split keys are either flat or round, and are used to promote a feeling of confidence concerning the safety of a certain joint-pin or bolt and nut. After the split key is put into its key-way, the split part that protrudes beyond the side of the joint-pin or bolt is opened, and a safe fastening is effected; and ordinary wear or proper usage of the key will not have the effect of unfastening, which must be accomplished by straightening the key in order to draw it from its key-way. Round split pins are extensively used, and for several years the wire for making such has been made by the manufacturers into a semicircular shape, so that by doubling the wire the split pin is formed. The split key is shown in Fig. 75; the split pin, by Fig. 76.

A split pin is also a split key, because both are used to lock or fasten pieces of machinery together. But the term split pin is properly applied to the circular variety, in order to make some approach to a distinction of technical terms and names. To make names definite, it is necessary that one name should not be used for more than one form.

The method of making the half-round wire into a split pin, fit for use, belongs to the portion of this work devoted to fitting; because no forging is required. But the split keys are sometimes made of large sizes, and, being forged in large numbers, demand some attention.

Small split keys are easily made by doubling the iron, and welding the two together at one end. After being welded, the solid part, which is to be formed into the head, may be held by the tongs while the stem is reduced to its dimensions. Although the stem is split, at the time of being drawn down, it will bear a large amount of hammering without breaking, if the heat of the key while on the anvil is not allowed to fall much below dull red. If the key is to have a head, and the amount of iron used not very important, the piece may be cut from the stem, in order to avoid drawing down.

Split keys, eight or ten inches in length, should be made from one bar, instead of welding together two bars. A solid bar can be easily divided at one end to form the split, by means of the rod-chisel or trimming-chisel. The chisel is driven half way through that part of the bar which is to be the edge, or small side of the key-stem; when it is cut half through, turn the key upside down, and drive the chisel through the uncut portion. When the opening is first made, it is ragged; and it is necessary to cut off all the ragged pieces previous to smoothing the two insides; because if the loose or semi-detached pieces are flattened with the key, it will be far from solid; and if the key should be afterwards very much drawn down, some part of it would break.

The method of smoothing the two insides is by a thick wedge being placed in the opening, and the key being drawn while the wedge is in. After being smoothed, the wedge is taken out and the key drawn without the wedge. The operation is shown by Fig. 77. It is proper to make the wedge of steel, because it will be useful for split keys of various sizes.

In addition to machinery for making half-round pin-wire, we have machinery for making split keys and other kinds of keys, at a quick rate, both of steel and iron. Large firms, who may require large numbers of the articles, can avail themselves of the opportunity, when the machinery shall have become adapted to produce the kind and size required by different individuals. And even at the present time, if those who require them will be careful to order the keys, so that, when received, they will be a little too large, instead of a little too small, the small amount of fitting necessary will not be of great consideration.

But these considerations have but little relation to the private learner's advancement in the art of forging. He will discover the great value of practice in key-making, because of his experience in the several different processes. And it is necessary for him to commence forging simple articles, that he may become skilful when forging compound ones.

When it is necessary to forge a number of flat keys with heads, and the keys are required to be of similar length, breadth, and thickness, the method consists in making a long bar of the required thickness of the keys, the width of the bar being a little greater than the required width of the key-heads.

The bar must be thoroughly welded and drawn down by the steam-hammer, being careful not to injure the bar by unnecessary hammering, or by making it too thin. Next to cutting off the ragged part that may be produced at the end of the bar, the end of it must be carefully squared, and then properly mark the size and shape of the keys upon the bar by means of a pencil. The marking thus produced is shown by Fig. 78.

This method is only available with proper care to make the bar the proper width and thickness, previously to commencing to cut. If each key is cut a little larger than it is required to be when finished, the process will economise time and metal. The correct way of marking consists in making a thin piece of sheet iron to the shape of the key-side. This piece of iron, when properly filed to the dimensions, is termed a gauge: the size of it should always be a little larger than the side of the key required.

The gauge is placed upon the bar, and a slate-pencil with a small end is used to mark the shape ; after which drive the chisel for cold iron into the middles of the pencil-marks. Both sides of the bar are to be marked, the operator being careful to make the marks opposite to each other, that he may avoid the danger of spoiling the keys. This disaster he can prevent by marking and cutting out a few, and then marking and cutting out a few more. To mark a great number before cutting out one is allowable, if the bar is marked upon one side only. The length and width of a gauge for keys ten inches long and four inches wide should not be more than one-sixteenth greater than the required keys.