It consists of two upright beams, called cheeks, about six feet long, tenoned into a cap above, and, at their lower ends, into a stout square frame, on which it stands. The head of the press is sustained by two iron bolts that pass through the cap. A screwed nut is fixed in the head, through which the screw works when operated upon by the lever; the lower extremity of this screw is called the spindle, which is a cylindrical piece of steel working in a metallic cup of oil, fixed to an iron plate let into the top of a broad solid, and thick piece of mahogany, whose surface is brought to a true and smooth plane, and is called the platten. This platten, by pulling the lever, is made to descend and press upon a blanket, which covers the paper laid upon the form of types, and thereby produces an impression. The form is laid upon a broad flat stone, or thick marble slab, which is let into a wooden frame called a coffin; this coffin is fixed upon a carriage, which is made to run upon a horizontal railway under the platten for an impression, and out clear of the same, to take off the printed sheet, and put a blank one in its place. This backward and forward motion of the carriage and form is produced by a strap and pulleys turned by a winch handle.
The paper is adjusted and held down by a folding frame, called the tympan and frisket, which again fold down over the fresh inked type, in a very exact manner, before the form is run in under the platten to receive an impression'. By presses of this kind, about 250 impressions are run off in an hour; in light work it is extended to 300 in an hour; and when presses of this kind were used for printing newspapers, the printers managed, by extraordinary efforts and relays of men, to work as many as 500 in the hour.
The principal defect in the common or old fashioned press just described, consists in the effective power of the lever being uniform throughout its range of motion, requiring the pressman to exert his bodily strength to the utmost, in giving it a tug at the end of the pull; at which time only, when the platten is down upon the form, great force becomes necessary This disadvantage is completely obviated in the improved press invented by the late patriotic Earl Stanhope which machine we purpose describing after having explained the principle upon which its chief excellence depends, namely, the combination of levers, by which the platten is forced down upon the form of types. In the annexed diagram a b represents a short lever, which is connected to the top of the screw which carries the platten, the shorter arm of the said lever being the radius of the screw; its longer arm the distance between the centre of the screw to the point b. This lever, by means of a connecting rod e, acts upon the bent lever deg, whose fulcrum is at e; and as, by this combination of the lever, the platten acts but through a small space in comparison to the space passed through by the power, it follows that the effect must be very powerful.
But it is necessary that this effect should be at a maximum when the platten impinges upon the type, and this object is accomplished by the angular position of the levers; for when the platten is elevated, the lever eg is parallel to the line h i, and its shorter arm e d is nearly perpendicular to the same line, and also the connecting rod c; therefore will move the rod c with its greatest velocity during the first part of the motion of the lever e g; at which time the lever ab forms an acute angle with the line k i; consequently acts at a disadvantage in causing the revolution of the screw; hut by the time the lever eg is brought perpendicular to the line hi (when the platten impinges upon the type) the lever ab is also perpendicular to the connecting rod c; consequently it will then exert its greatest influence in causing the revolution of the screw, and at this time also the power of the workman will be applied at right angles to the lever eg, therefore will produce the greatest effect precisely at the moment of impact.
The "Stanhope press" is, in other respects, a considerably improved machine. The whole frame is made of one massive iron casting, as repre, sented at kk in the subjoined cut, which exhibits a perspective view of it In the upper part of the machine a nut is fixed, into which a stout, wel cut screw l works, having a conical end that operates upon the upper end of a slider m, which is fitted into a dovetailed groove formed between two vertical bars n n of the frame. The slider has the platten o firmly attached to the lower end of it; and being accurately fitted in the guide bars n n, the platten rises and falls parallel to itself, when the screw l is turned. The weight of the platten and slider is counterbalanced by a heavy weight p, which is suspended from a lever, that acts upon the slider to lift it up, and keep it always bearing against the point of the screw. At q is a forked support to the railway and carriage. The carriage is moved by a winch or "rounce," with a "spit" and leather straps, which pass round a pulley r, one strap extending to the back of the carriage to draw it in, and two others pass round the wheel in an opposite direction, to draw it out: s is the table on which the type is laid.
The combination of levers in this machine, it will be observed, is precisely the same as in the preceding diagram, and their action is the same; consequently further description of them is omitted.
The superiority of iron presses over the wooden ones may, in a great measure, be attributed to the extreme accuracy with which the corresponding surfaces of the platten and table are levelled. This is effected by turning them m the lathe, with a slide-rest; and this is performed with such precision that if they do not bite a hair or a thin piece of paper in every part, they are not considered to be finished. The advantage of true workmanship must be apparent in printing such surfaces as those of our large newspapers, and clearly bringing up every letter and dot out of perhaps a hundred thousand or more.