(Continued from page 189.) HAND PRESSESmdash;The mighty printing machine counts its hourly productions by thousands, the humble hand-press produces at the utmost but a few hundred impressions in the same time ; such being its vast inferiority, its total disuse would appear inevitable, and yet, contrary to this inference, the hand-press maintains its position, chiefly owing to its simplicity and consequent cheapness. As any kind of pressure is sufficient to obtain an impression on paper, a printing press might be an exceedingly simple machine, but it is made complex in order that the printing may be done well and rapidly. The first hand-presses were merely common screw-presses made of wood, and such, with slight improvements, they remained until within the last half century, when iron superseded wood in this machine, as it has in most others; nor was this the greatest change, for the screw was first improved by the addition of well-arraBged bars, then totally abandoned, as not permitting sufficient rapidity, and its place supplied by compound levers. But without tracing its successive de-velopements, let us content ourselves with examining the hand-press as it is now generally made. The frame is composed of a heavy mass of cast-iron, and consists of a stout head piece connected to an under piece neatly similar, by two strong columns. It will be easily understood that the whole of the pressure exerted has to be endured by these two cross-pieces of the frame, whence the necessity tor their being made massive. On the under piece are placed the ribs, which form, as it were, a railroad, on which moves the bed destined to bear the type. Over the bed is suspended the platen which is intended, by being forced down, to press the paper against the type. This is effected by levers, having a fulcrum on the under side of the head piece, and bearing on the centre of the platen; the power ol the pressman is further increased by the bar-handle, which is also a lever acting on those we have just mentioned, so that the whole arrangement forms a compound lever of great power, and which furnishes an exemplification of the law of virtual velocities. For the pressman grasping the bar-handle near its extremity, his hands describe an arc of a circle, whose diameter is considerable, whilst by this action the platen is made to descend through only a small space, but capable of overcoming a great resistance. When the impression is imparted, the next thing to be done is to raise the platen from the form, which is performed without occasioning any trouble to the pressman, for he simply relaxes the intensity of his grasp, wken the platen is pulled up by spiral springs with considerable energy. The next duty of the pressman is to turn a crank, by which the bed (on which are lying the form and paper) is moved from under the platen, so that he can raise the blanket, the tympan frame, and the frisket. All which form the apparatus for securing the paper and preventing any injury to it from the type. Whilst he is occupied in detaching the printed sheet, and then fixing another to the tympan frame, the type receives a fresh supply of ink from a roller, impelled by means to which we will hereafter advert. The tympan frame is now folded down on the form and the bed made to resume its place under the platen, when the work of printing is resumed, all these several operations being performed 250 or 300 times per hour. In some hand-presses the bed is not movable but remains stationary, whilst the tympan frame alone is run out, and during its absence from its position on the bed, an inking roller is made to move over the form, which retires in time to allow the tympan frame to resume its original situation. For convenience, the press is placed upon standards to raise it to a sufficient height, so that the bar. handle which moves in a horizontal plane can be worked by the pressman, without the necessity of inclining the body. Such is a description of the machine more especially known as the hand-press, but a variety of presses that may be worked either by the hand or foot, are like-wisejnanufactured. Probably the most ingenious ot these latter are the card presses, now so much, used by printers, they are intended for expedition, and as the form contains but a tew pieces of type, a small bed and platen of about the size of the cards to be printed are placed vertically opposite to each other. The platen is stationary, and two small guides that are fixed to the upper part conduct the cards to their place on the platen, where they are held by a light spring. On the bed is fixed the form, and when the type is inked the bed is forced against the platen by a cam, it then runs back, when the card is released and drops into a box, whilst the printer who keeps the press at work by a treadle, can supply another card to the platen. Not the least ingenious part of the mechanism is the inking apparatus which is self-acting, a fountain with the usual arrangement of rollers being placed above the bed and platen, when the bed has retired some distance from the latter, it stops, and an inking roller runs down, pressing against the type in its progress, and as quickly re-ascends. Nor is this the only form of the card press, many excellent machines of different shapes have been invented, some otthe best kinds of which will be found described in the preceding volumes of the Scientific American. For example, in one kind the platen moves on a pivot, and is lorced down by a roller on a vibrating angular piece, which latter also supplies an inking board ; (see Sci. Am., Vol. 7, p. 316). In another (Gordon's Card Press) the form is attached to a revolving cylinder, ar.d the paper or card-board, in an endless web fed down to a flat bed, and as the cards are printed they are cut off. The supply of ink to the type is an important subject of consideration to the printer his predecessors used inking cushions or balls formed of sheep-skin, and stuffed with wool; yet later, a boy provided with a roller composed of a mixture of molasses and glue, supplied the form with ink after each impression, but it is now very common to have for this purpose a separate machine, termed an inker. There are various sorts of this apparatus, some of which are more simple but less convenient than others, but almost all employ a fountain or reservoir. In this fountain a roller is made to revolve, and as the ink, irom its unctuous nature, is likely to collect in masses on the roller, a steel straight-edge is made to bear against it, and thus act as a scraper. Another roller that, in addition to its rotary movement, also vibrates lengthwise, receives the ink from the above, and finally, alter these or further additional transfers, the ink is yielded to composition rollers, which are placed on carriages so as to be propelled over the form. It is in the mode of effecting this latter processthat the inkers mostly differ, perhaps that which is worked by steam power is the neatest. In this case it is placed by the side of the press, so that the roller carriage easily runs on to the press bed. To operate it, the pressman, after raising the tympan, merely touehes a handle, when the cog wheels which impel the carriage are thrown into gear, and, by a crank motion, turn a spindle, to which is attached one extremity of a long elbow joint. The other extremity is attached to the roller carriage, which, consequently, moves forward along the press bed, and afterwards returns, during which time the inking rollers bear against the type, the whole operation resembling the actions of a man who might hold a cylindrical body between his fingers and roll it back and forwards on a table. When the carriage has returned, the wheels are thrown out ef gear, and then, although the distributing and other rollers are revolving and supplying the ink, the carriage is unable to move forward until the pressman desires. On the use of gutta percha and papier ma-che stereotype cylinders, we will here make no comments, but wait until something practical has resulted ; there is, however, a species of printing which has made advances equal to those already mentioned, and to which its processes are often very similar,mdash;we allude to calico printingmdash;all the cheaper cottons being now printed by a cylinder press. The pattern is engraved on the surface of a copper cylinder, which, by mechanism, is made to feed itself with color, take off what is superfluous, drawin the material to be printed, and then perform the printing. In this process several cylinders are employed (every colorrequiring a separate one), which are ranged around a large drum, each copper cylinder being supplied with its own trough of coloring matter ind attendant rollers. To effect the printing, the cotton is passed between the large drum and the printing cylinders, which, in some recent presses of this description, amount in number toeight; an improved Calico press has been lately introduced by which each copper cylinder can be made to print in three or lour colors by a novel arrangement;mdash;this is the mode of printing ordinary articles, but those of a costlier kind are still printed by the block method.
This article was originally published with the title "Machinery and Tools as they are.—Printing Presses"