The merits of the Stanhope press, and its superiority, are so well established in the minds of printers, from long experience of its valuable properties, that any additional praise from me would be an act of supererogation; I shall therefore confine myself to giving engravings of it, and a rather full description.
Figs. 1. and 2. are elevations, fig. 3. a plan, and fig. 4. a section. A A is a massive frame of cast iron, formed in one piece: this is the body of the press, in the upper part of which a nut is fixed for the reception of the screw b, and its point operates upon the upper end of a slider, d, which is fitted into a dovetail groove formed between two vertical bars, e, e, of the frame. The slider has the platen, D D, firmly attached to the lower end of it; and being accurately fitted between the guides e, e, the platen must rise and fall parallel to itself when the screw, b, is turned. The weight of the platen and slider are counterbalanced by a heavy weight, E, behind the press, which is suspended from a lever, F, and this acts upon the slider to lift it up, and keep it always bearing against the point of the screw. At G G are two projecting pieces, cast all in one with the main frame, to support the carriage when the pull is made; to these the rails, H H, are screwed, and placed truly horizontal for the carriage, I, to run upon them, when it is carried under the press to receive the impression, or drawn out to remove the printed sheet. The carriage is moved by the rounce or handle K, with a spit and leather girths, very similar to the wooden press. Upon the spit, or axle of the handle K, a wheel, L, is fixed, and round this leather girths are passed, one extending to the back of the carriage to draw it in, and the other, which passes round the wheel in an opposite direction, to draw it out. By this means, when the handle is turned one way it draws out the carriage, and by reversing the motion it is carried in. There is likewise a check strap, f, from the wheel down to the wooden base, M M, of the frame, and this limits the motion of the wheel, and consequently the excursion of the carriage. The principal improvement of Earl Stanhope's press consists in the manner of giving motion to the screw, b, of it, which is not done simply by a bar or lever attached to the screw, but by a second lever; e. gr. the screw, b, has a short lever, g, fixed upon the upper end of it, and this communicates by an iron bar, or link, h, to another lever, i, of rather shorter radius, which is fixed upon the upper end of a second spindle, l, and to this the bar or handle, k, is fixed. Now when the workman pulls this handle, he turns round the spindle, l, and by the connexion of the rod, h, the screw, b, turns with it, and causes the platen to descend and produce the pressure. But it is not simply this alone, for the power of the lever, k, is transmitted to the screw in a ratio proportioned to the effect required at the different parts of the pull; thus at first, when the pressman takes the bar, k, it lies in a direction parallel to the frame, or across the press, and the short lever, i, (being nearly perpendicular thereto,) is also nearly at right angles to the connecting rod h; but the lever, g, of the screw makes a considerable angle with the rod, which therefore acts upon a shorter radius to turn the screw; because the real power exerted by any action upon a lever, is not to be considered as acting with the full length of the lever between its centres, but with the distance in a perpendicular drawn from the line in which the action is applied to the centre of the lever. Therefore, when the pressman first takes the handle, k, the lever, i, acts with its full length upon a shorter length of leverage, g, on the screw, which will consequently be turned more rapidly than if the bar itself was attached to it; but on continuing the pull, the situation of the levers change, that of the screw, g, continually increasing in its acting length, because it comes nearer to a perpendicular with the connecting rod, and at the same time the lever, i, diminishes its acting length, because, by the obliquity of the lever, the rod, h, approaches the centre, and the perpendicular distance diminishes; the bar or handle also comes to a more favourable position for the man to pull, because he draws nearly at right angles to its length. All these causes combined have the best effect in producing an immense pressure, without loss of time; because, in the first instance, the lever acts with an increased motion upon the screw, and brings the platen down very quickly upon the paper, but by that time the levers have assumed such a position as to exert a more powerful action upon each other, and this action continues to increase as the bar is drawn forwards, until the lever, i, and the connecting rod are brought nearly into a straight line, and then the power is immensely great, and capable of producing any requisite pressure which the parts of the press will sustain without yielding. The handle is sometimes made to come to rest against a stop, which prevents it moving further, and therefore regulates the degree of pressure given upon the Work; but to give the means of increasing or diminishing this pressure for different kinds of work, the stop is made moveable to a small extent. Another plan is adopted by some makers of the Stanhope press, viz. to have a screw adjustment at the end of the connecting rod, h, by which it can be shortened; it is done by fitting the centre pin which unites it to the lever, g, in a bearing piece, which slides in a groove formed in the rod, and is regulated by the screw. This shortening of the connecting rod produces a greater or less descent of the platen, when the handle is brought to the stop.
The carriage of the press is represented with wheels, m, m, beneath, to take off the friction of moving upon the ribs, HH. These wheels are shown at fig. 4., which is a section of the screw and the platen, with the carriage beneath it: their axles, n, are fitted to springs, p, and these are adjustable by means of screws, r, so that the carriage will be borne up to any required height. This is so regulated, that when the carriage is run into the press, its lower surface shall bear lightly upon the solid cheeks, G, which are part of the body of the press, and these support it when the pressure is applied, the same as the winter of the old press: but the wheels by their springs act to bear up great part of the weight of the carriage with the types upon it, and diminish the friction, yet do not destroy the contact of the carriage upon the ribs, because this would not give the carriage that solidity of bearing which is requisite for resisting the pull. This is only at the time when the carriage is run into the press, because as it runs out, the ribs on which the wheels run rise higher, and therefore the wheels support the whole weight. The manner in which the wheels run in rebates or recesses in the edges of the ribs is shown at fig. 1. The carriage is made of cast iron, in the form of a box, with several cross partitions, which are all cast in one piece, and although made of thin metal, are exceedingly strong: the upper surface is made truly flat, by turning it in a lathe. The same of the platen, which is likewise a shallow box: the slider, d, has a plate formed on the lower end of it, which is fixed by four screws upon the top of the platen, and thus they are united. At the four angles of the carriage, pieces of iron are screwed on, to form bearings for the quoins or wedges which are driven in to fasten the form of types upon it in the true position for printing. The tympan, P, (fig. 2.) is attached to the carriage by joints, with an iron bracket or stop to catch it when it is thrown back: the frisket, R, is joined to the tympan, and when opened out, rests against a frame suspended from the ceiling. The register points are the same as in the wooden press, and all the operations of working are exactly the same. The iron frame, A, of the press is screwed down upon the wooden base, M, by bolts, which pass through feet, s s, projecting from the lower part of the iron frame. Another wooden beam is fixed into the former at right angles, so as to form a cross, which lies upon the floor. The ribs, H, for the carriage to run upon are supported from the wooden base by an iron bracket, T.
The advantages of the iron presses in working are very considerable, both in saving labour and time. The first arises from the beautiful contrivance of the levers, the power of the press being almost incalculable at the moment of producing the impression; and this is not attended with a correspondent loss of time, as is the case in all other mechanical powers, because the power is only exerted at the moment of pressure, being before that adapted to bring down the platen as quickly as possible. This great power of the press admits of a saving of time, by printing the whole sheet of paper at one pull, the platen being made sufficiently large for that purpose; whereas, in the old press, the platen is only half the size of the sheet. In the Stanhope press, the whole surface is printed at once, with far less power upon the handle than the old press. This arises not only from the levers, but from the iron framing of the press, which will not admit of any yielding, as the wood always does, and indeed is intended to do, the head being packed up with elastic substances, such as scaleboard, pasteboard, and the felt of an old hat. In this case much power is lost, for in an elastic press the pressure is gained by screwing or straining the parts up to a certain degree of tension, and the effort to return produces the pressure: now in this case, the handle will make a considerable effort to return, which, though it is in reality giving back to the workman a portion of the power he exerted on the press, is only an additional labour, as it obliges him to bear the strain a longer time than he otherwise would. The iron presses have very little elasticity, and those who use them find it advantageous to diminish the thickness of the blankets in the tympan; the lever has then very little tendency to return; in fact, if the pull be so justified as that, when the bar is pulled home, the end of the lever, i, that is attached to the connecting rod, h, passes in a small degree the centre of the second spindle, I, the pressure is past its maximum power, the press bar has no tendency to return, and the pressman can rest upon his pull in fine work, without any exertion.