60 degrees; or by two cutters each hollowed to 90 degrees. In the three cases, the wire is respectively cut from two, three, or four equidistant parts of its circumference; semicircular cutters are also used. The straight cutters first named, are moreover very usefully employed in the fly-press for many of the smaller works, that would otherwise be done with shears.
Sometimes the succession of the links for the chain, is one and two links alternately as at b, fig. 956; at other times 3 and 2, or 4 and 3 links, as at c, and so forth up to about 9 and 8 links alternately, which are sometimes used, and the wires when inserted are slightly riveted at the ends.
The pin is generally the weakest part of the chain and gives way first, but in the chains with 8 and 9 links, the pin must be cut through at 16 places simultaneously, before the chain will yield.
Chains are sometimes intended to catch on pins or projections, around a wheel of the kind shown in fig. 958, to fulfil the office of leather bands, without the possibility of the slipping, which is apt to occur with bands when subjected to unusual strains.
Such chains are made after the manner shown in fig. 957, to constitute the square openings that fit over the pins of the wheel, the central links are made shorter, by which means the apertures are brought closer together than if the longer links were used throughout. Fig. 959, shows a different kind of chain, that has been used for catching in the teeth of an ordinary spur wheel with epicycloidal teeth, the author believes this chain to have been invented by the late Mr. John Oldham, Engineer to the Bank of England.
Chains for watches, time-pieces, and small machinery, are too minute to be made as above described, therefore the slip of steel is first punched through with the rivet holes required for a number of links, by means of a punch in which two steel wires are inserted; the distance between the intended links is obtained, (somewhat as in file-cutting,) by resting the burrs of the two previous holes, against the sharp edge of the bed or bolster. The links are afterwards cut out by a punch and bolster of the kind already noticed, but very minute, and the punch has two pins inserted at the distance of the rivet holes, the slip of steel being every time fitted by two of the holes to these pins, all the links are thereby cut centrally around the rivet holes.
The tools are carried in a thick block having a perpendicular square hole, fitted with a stout square bar, the latter is driven with a hammer, which is supported on pivots, raised by a spring, and worked by a pedal; but when the links measure from 1/4 to 1/2 an inch in length, such tools are worked by a screw.
The punches are fitted to the side of the square bar, in a projecting loop or mortise, and secured by a wedge. They are drilled with holes for the pins, and across each punch there is a deep notch to expose the reverse ends of the pins, in order that when broken they may be driven out and replaced. The pins are taper-pointed, that they may raise burrs, instead of cutting the metal clean out, and being taper, no puller-off is required, and the bed tools are fitted in chamfer grooves in the base of this old yet very efficient instrument.
A large chain for a pocket chronometer now before the author, measures nearly 14 inches in length, and contains in every inch of its length 22 rivets and also 33 links, (in three rows); the total number of pieces in the chain is therefore 770, and its weight is 9 1/2 grains. A chain for a small pocket watch, measures 6 inches in length, and has 42 rivets and 63 links in every inch, in all 630 pieces, and yet the entire chain only weighs one grain and three quarters.
The square links of chains for jewellery are often cut out with punches, the exterior and interior being each rectangular; after which each alternate link is slit with a fine saw for the introduction of the two contiguous links, and then soldered together so that the gaps become filled up. Other chains are drawn as square tubes, and cut off in short lengths with a saw, these after having been strung together are often drawn through a draw-plate with round holes, to constitute chains which present an almost continuous cylindrical surface like round wire; a very neat manufacture invented in France.
The teeth of saws are for the most part cut in the fly press. Teeth of the forms figs. 643 to 647, page 684, whether large or small require but one punch, the sides of which meet at 60 degrees. Two studs are used to direct the edge of the blade for the saw to the punch, at the required angle depending on the pitch or inclination of the teeth, and an adjustable stop determines the space or interval from tooth to tooth, by catching against the side of the last tooth previously made. Gullet teeth, figs. 650 to 653, and the various other kinds shown, require punches of their several compounded figures, and of different dimensions of each size of tooth.
The teeth of circular saws are similarly punched out by mounting the perforated circular disk on a pin or axis, but in cutting the last six or eight teeth, it is needful to be watchful so as to divide the remaining space into moderately equal parts.
In cutting the teeth of circular saws not exceeding 12 inches diameter, Holtzapffel and Co. have been in the habit of mounting the steel plates on a spindle in a lathe with a dividing plate, and using a punch and bed fitted to a square socket, fixed horizontally in the ordinary rest or support for the turning tool, the punch being driven through the plate by one revolution of a snail or cam, by means of a winch handle, and thrown back by a spring. In this arrangement the dividing plate ensures the exact dimensions and equality of the teeth, which are rapidly and accurately cut.
The copper caps for percussion guns are punched out in the form of a cross with short equal arms, or sometimes in a similar shape with only three arms, and the blanks, after having been annealed, are thrown into form by means of dies, which fold up the arms and unite them to constitute the tabular part, whilst the central part of the metal forms the top of the cap that receives the composition, and sustains the blow of the hammer.