The work of the spring smith has been considerably curtailed by the introduction of a compact machine, which combines all the processes of shearing, tapering, spearing, or shaping the ends of the plates, punching, slotting and nibbing, for which, up till now, if machinery has been employed, it has been requisite to use separate machines. It occupies a space of about 12 by 8 feet over all, including arms for resting plates upon and adjustable guides for lengths. It consists of an upright frame carrying three slides in the centre, working respectively to a couple of dies for spearing or shaping the ends of the plates, putting in the nibs, and a punch for cutting the horizontal slot. A fourth slide is utilised for the working of a circular punch to form the centre indent for the ¾-inch set screw, and above this is a pair of shears for cutting the bars to length, to which is attached an arm for an adjustable guide for those lengths.

At the opposite end of the machine is a pair of rolls, one of which turns eccentrically and tapers the ends of those plates which are required for certain classes of springs. Alongside this, fixed to a back centre, there is an arm which rests upon a cam, and its duty is to close in again the metal which has spread during the thinning process. If only one width of plate was used, this last piece of mechanism would not be required, as a groove in the roll would prevent the metal from spreading. The whole combination can either be driven from the shafting, or, where this is absent, by a small vertical engine with ordinary gearing, and is operated by one man. For all ordinary grades, say up to about 48 tons per square inch tenacity, this machine operates upon the plates at ordinary temperatures, but should a harder grade be required, the plates are got to a dull red heat before being machined, and then portioned out in complete sets to the various smiths. The pin ends of the spring back are stamped in blocks from a good quality iron, which in the long run is the most economical, because they can be cut out of damaged backs and welded on to new ones, and should the holes wear they can easily be closed again, whereas if made from any grade of steel beyond a mild, it would be more difficult to cut them out and close the holes, or re-weld in new backs.

Solid ends are prepared by turning the plate round a piece of «-inch iron, welding up and finishing in a swage fixed on the anvil Fig. M. Each smith has a setting table about 5 by 2 feet 6 inches by 4 inches thick, and a block to sketch, Fig. L, also a good set of cramps to assist in placing on the buckles, and one oil tank 4 feet in diameter by 5 feet 6 inches deep serves for two hearths. The use of the block chiefly lies in rectifying the cambre of plates after tempering, for although the tendency is to straighten, it is never known in which direction the plate may go or behave during slacking - one edge may go more than another - also for bringing to cambre any plates that have been damaged through accident or unusual wear and tear. Each smith makes his own backs by welding on the ends, which have been drilled for the pin, and clearance slotted for the link. This job alone shows the smart action required in welding steel of moderately high carbon, for the backs are a special welding grade not quite so hard as the body of the spring. After each end has been welded on, a composition being used to aid this, the whole is got to a uniform heat and the cambre set in to a template, and then followed on by each succeeding plate to the preceding one. Each, as it passes through the smith's hand, is hardened and tempered in oil, the latter operation generally depending upon the behaviour of the heated plate when rubbed with a piece of wood. Judgment in this case depends entirely upon the knowledge of the grade of steel, any change in which can easily be detected by its ring when struck, but sometimes in the case of safety valve springs, one or two are tried in the testing machine. The collection of plates is then cramped together, and the buckle. Fig. 246, p. 145, is placed on hot, compressed upon all sides simultaneously in a specially designed hydraulic press, and then quenched.

Fig. 271.

Every spring is tested to a pressure sufficient to take out the cambre, not more than ⅛ or 3/16 inch permanent Bet being admitted. The finished spring is shown in Fig. 271. The safety valve spring consists of six coils of 25/32 inch diameter steel bar, one half of a coil at each end being turned inwards for suspension. The length between the points of suspension is equal for 140 lb. and 160 lb. per square inch, the difference in the tension being effected generally by temper, but it may also be regulated by composition of the metal or reduction in sectional area. It, and the mandril upon which it is made are shown in Fig. 272, which will also serve as an example of the production of this class of spring. Owing to the strong section of some volute springs, the motion of the mandril must be produced by mechanical effort.

Fig. 272.

Among the processes accessory to smiths' work, it may be stated that tempering in its broadest sense embraces hardening, case-hardening, annealing and toughening. Considerations to be regarded when effecting a certain degree of temper are resistance to abrasion, the sustaining of a great pressure upon a cutting edge, and also the elasticity of the remaining portion of the tool or article in hand. The intrinsic value and total efficiency of a tool depends much more upon the manipulation of the operator during its production, and its tempering qualities, than upon its direct hardening property. The former is adjusted to suit the nature of the work it has to perform, and is really the obtaining of a hardness with resilience, less than the ultimate or dead hardness. The heating should he as uniform as possible, otherwise there will be an unequal expansion, and sometimes to such an extent as to render the finished article of very little value. The rapidity with which the heat should be developed depends entirely upon the size and the utility of the article; but in most cases it is safe to state that slow and even heating should be resorted to, with as little decarbonisation going on as possible, but if the article is of large dimensions and even section, it may be of considerable service to heat the exterior rapidly and evenly, then, after cooling, the interior will he of a lower temper than the exterior, and consequently the article will be backed up with an interior of greater resilience than the exterior. Hardness is the direct result of quenching, which should be carefully done, so as to prevent as much as possible, warping and cracking; rectifying any deviation from the straight being possible by careful insertion in the cooling medium.