The shaping here specially referred to, is that by which the curved slots of valve-links are produced. But it will be necessary to briefly mention also the planing of their broad sides, and the slotting of their outer edges or narrow sides.

Link-slots are so formed, that when newly produced, their curves constitute portions of circular arcs which are parallel to each other; consequently, the width or distance between the two sides is the same as at any place along the slot. It may be also mentioned here, that nearly all link-pieces when just forged, consist of flat bars or slabs of steel or iron devoid of any slot, or hole whatever.

There are four modes of shaping links, and the mode which should be adopted in any one case, depends on the resources of the maker, and the number of links he may have to shape. A link-slot can be easily formed with drilling, chipping, and filing, without using any other shaping apparatus. Slotting a link, while on an ordinary slotting-machine, is also resorted to. A link may be slotted also while on a lathe-chuck; or while on the table of a short-stroke slotting-machine specially adapted to the purpose.

A piece intended for a link is first planed to make both broad sides parallel with each other, and reduce the piece to a suitable thickness. To hold the piece during planing, it may be provided with a couple of holders or handles, one at each end, and forged solid with the link-piece; or it may have a couple of holes drilled in some part of the place which will become the slot, these holes being provided with recesses which are large enough to contain nuts. A link thus held for planing is shown in Fig. 691. After the planing is completed, one of the broad sides is scribed to show the intended outer shape of the link, and to show the place and shape of the slot. This scribing is executed by means of a template, if a number of links are required to be of the same shape and size, to avoid the necessity of marking each one separately. But to scribe a link-piece without a template, it is put upon a table of sufficient length, and the arcs are marked with a radius gauge, one point of the gauge being put into a dot which is made into a block on the table, the block being of the same thickness as the link, and fastened on the table at a suitable distance from the link.

Although link-slots are finished by one of the four modes mentioned, they are always principally formed with drilling, vertical drillers being used for the purpose. The amount of metal removed with drilling is thirty or forty times the quantity taken out with either of the finishing processes, and there is no other class of machines which will so quickly remove the superfluous metal.

When a link has been lined, the drilling is performed both to produce the slot, and to remove the greater portion of the metal from the link's outer edges, if sufficient metal exists at the edges to admit a drilling. The drilling for the outer edges consists in making a row of small holes around the link close to the gauge lines. For drilling the slot, the mode selected depends on the size of the work. If the required slot is to be only about an inch and a half wide, a single row of holes are made along the middle of the slot, with a drill about a quarter of an inch smaller in diameter than the slot's width. But a slot of two, three, or more inches in width, is formed by drilling two rows of small holes, one row at each side, and also a few other small holes, or one large one, at each end. The drills used for this purpose need not be more than half an inch or three-quarters in diameter; and by such drilling, nearly the whole of the slot-piece can be removed in one lump.

In order to completely detach the slot-piece it is either chiselled or slotted. If the piece is small it is gripped in a vice, and the thin portions between the holes are cut through with a hammer and chisel. But if the link is to be machined, the slot-piece is removed in the course of shaping with the slotting-tools. A mortiser or a grooving-tool of proper width is first fixed and caused to cut two narrow slots or channels along the places occupied by the holes, thus removing the thin portions between the holes, and therefore the entire slot-piece also.

One of the modes referred to for accurately finishing a link-slot, consists in fixing it upon a slotting-table having a circular movement, and paring the slot-sides with a tool during the gradual movement of the link with the table. Any slotting-machine having a table of sufficient diameter can be used for this purpose, the link being fixed on the table so that the curves of the intended slot are exactly concentric with the table's rotary motion, and therefore concentric with the parallel circular gauge-lines existing on the table. In order to keep the link at a proper height above the table to allow room for the slotting-tools, and to keep its planed broad sides parallel with the table, it is put upon parallel blocks which are situate along each edge of the slot, and very near it, being only far enough from the edges to allow room for the cutting-tools to extend through without touching the blocks. Holdfast-plates are now placed at the outer edges, and the link is adjusted with poppets which are fixed to the table. To ascertain the exact relative position of the gauge-lines a pointer is fixed in the tool-holder, so that its point is very near one of the lines, and the table and link are next partly rotated while the observer watches the progress of the line beneath the point. As soon as the point is seen to exactly coincide with the line during its entire passage beneath the pointer, the link is adjusted. The slotting can therefore now commence, and one side of the slot can be finished.

In order to finish the opposite side of the slot, the link is shifted, and again adjusted; but this time to the opposite line, that the side having this line may be put near enough to the tool. After each fixing of the link, it is necessary to adjust the tool also ; because, when an ordinary slotting-table is employed, it may not be capable of the movement suited to the adjustment of such objects as links.

Another of the modes for finishing a link-slot, consists in shaping it with a small slotter which is specially adapted to the purpose. This machine resembles any other slotter, excepting that its table is not capable of being entirely rotated, and that it is furnished with an extra couple of slides and adjusting screws, for adjusting the links to suit the situations of the slotting-tools. The table need not be circular; it is sufficient if it consists of about a quadrant; consequently, instead of requiring a complete circular worm-wheel, about a quarter of one would suffice. By adopting such a table, the amount of room which would be occupied by a round table is economised. In addition to the movement for accurately adjusting a link beneath a slotting-tool after the gauge-lines have been put concentric with the circular motion, the tool-holder also should have a movement by means of an adjusting screw to properly place the tool.

Another mode for accurately finishing a link-slot now remains to be mentioned, in which the use of a lathe is involved. This is a convenient mode if a lathe having a large disc-chuck is available. The link is first drilled to remove the greater part of the metal, as before stated, and is next attached to the lathe-chuck by means of parallel blocks, the blocks being first fastened to the chuck, and the link next fastened thereto with plates and bolts. The exact part of the chuck occupied by the link depends on the radius of the link's curves. Only one adjustment is sufficient for the shaping of both sides, because the slide-rest will adjust the tool after the link is fixed; and while being adjusted, the point of a tool held in the tool-holder is situate very near one of the gauge-lines. The lathe-chuck is now partly rotated to and fro by one or two assistants, while the operator observes the relative position of the point and the curved gauge-line. To shift the link easily and exactly to its proper place, a few poppets are fastened in the chuck, near the link, which poppets are very small, because the object is not to be mainly held with them, but with the holdfast plates on the broad sides. These plates can be very firmly tightened upon the link without distorting it; whereas, poppet-screws are liable to alter the shape of the entire link, if screwed too tight. It is, therefore, necessary to exactly adjust the object by the gauge-line previous to finally tightening the holdfast bolts.

This method of slot-shaping with a lathe, can only result in paring the metal from the slot-sides ; the ends must be shaped by other means, either by chipping and filing, or by slotting; and in either case, they should be finished previous to fixing the link to the lathe-chuck. In addition to finishing these ends, it is also requisite to finish a short portion of each of the two sides, at both ends of the slots, in order that the cutting tools may have room to enter into and disengage from the metal.

When the link is attached to the chuck, the operation of slotting consists in partly rotating the chuck to and fro a proper distance, while a slide-rest tool is in contact for removing the metal. The tools employed are ordinary borers, the ends of which are right-handed and left-handed, to cut both sides of the slot. The chuck is moved to and fro by the assistants, who actuate the chuck by working the leather band, or by rotating one of the power-spindles belonging to the lathe spindle-frame, the end of such spindle having a square part that fits a handle. In order to prevent the chuck being moved too far in either direction, and thereby breaking the tool or doing other mischief, a couple of stops are fixed in the chuck at a proper distance apart; these are situate at the chuck's lower edge, and are caused to come into contact with the lathe bed's side, or into contact with a couple of brackets or plates bolted to the bed.

To cause the slot-sides to be parallel with each other, and also square to the broad sides of the link, when the slot is finished, the top slide of the rest is adjusted, so that its length is square to the chuck-face, and this one adjustment of the rest is sufficient for the shaping of both sides. But it is also, in most cases, requisite to further adjust the rest, after both the slot-sides have been shaped and nearly finished, at which time the slot is measured with an inside calliper, and the slide rest is altered accordingly.

During the upward or backward motion of the work, the tool-point is in contact with the metal, the same as during the downward movement, although it does not cut; and to prevent the point of the tool breaking during the up-stroke, it is necessary to use a tool having a thick strong stalk, which is less liable to bend and dig into the metal than a tool having a slender stalk.

After a link-slot has been shaped by one of the methods here indicated, the link is completed by paring its outer edges. The most suitable machines for this purpose are shapers and slotters ; and the link is fastened on the table with two or three holdfast plates having bolts extending through the slot of the link.

The boring of a link consists in accurately forming its circular holes with a vertical drilling-machine. These are first roughly drilled with ordinary drills, and afterwards completed with rosebits, which will produce holes having smooth surfaces, and which are square to the link's broad sides, as desired. The boring of these holes can be finished either previous to the shaping of the outer edges or afterwards.