We have already mentioned, that the lower ends of the bolts b, b, which are generally shaped like the frustum of a wedge, gn into a hollow of the same form when the platen is pulled above the types. The object of this is to lock' the platen to the compound lever* EFGHKL, which, when moved by the handle H, presses the platen upon the types. This part of the apparatus consists of two levers DF, DF, moving upon fixed centres at D, D. The clutches, or wedge-shaped cavities, are joined to these levers near the fulcra D, D, so that when the extremities F, F of the levers DI:, DF are pulled down, the clutches are also pulled down, and therefore pull down the platen to which they are locked. The descent of the ends F, F is produced by a link G united to both, and this link is again joined to another lever, whose fulcrum is at K, while the other end is connected with the handle 11, by which the pressure is given. These levers are so arranged, that the maximum force is given when the platen just begins to touch the tympan. The platen in Mr. Ruthven's large presses is the size of a full sheet ; and, in consequence of the pressure not being propagated from its centre, the pressure over the whole sheet becomes more equable than in other presses. This press has also the advantage of being much cheaper than the Stanhope press, and other presses upon a similar construction.
lever with the second lever n, 6, moving on a fixed centre at o, in the great frame. Another link p is connected by an universal joint to n at one end, and at the other to the lever or handle H, at which the pressman works. This handle turns on a fixed centre pin extended from the great frame.
On the top of the vertical bars at n is placed the fulcrum f, of the counter-lever g, f, It, which carries an adjustible counter-weight W, the end g being united by a link to the end L of the main lever. The use of this counter-weight is to raise the main lever into its acting position, after the handle H has been let go by the pressman.
Barclay's .11merican Press.
This press has been lately introduced into this country from America, by Mr. David Barclay, its inventor. The great parts of the machine it is unnecessary to represent, as it is only the method of giving the pressure to the pla ten that gives it its chief interest. We have, therefore, represented this in Fig. 7, where A, A represent the two *upper inclined plates, and B, B the under one, which is fixed on the top of the platen, while the upper one A is fixed to the head of the press. A wedge NV, made of well hardened steel, is fixed to the end of the lever handle of the press, so that when this handle is pulled, the wedge \V is forced between two steel rollers C, D, so as to roll them along between the two inclined steel plates, and 'con sequently leave the lower plate 11 and the platen to descend. The left hand figure represents the rollers when the platen is pressed down ; and the right hand onethe same rollers when the platen has risen to its place of rest. The lever handle H moves round n as a fulcrum, and by increasing or diminishing a connecting link the required force is ob tained.
As the rollers are necessarily above the centre of the platen, the platen is guided in its ascent and descent by two metallic bars, not very distant from its margin, and at the top of each of these bars there is a spiral spring, which bears against the lop of the frame, and by balancing the weight of the platen, keeps it always clear above the tympan when the handle is at rest.
Clynzer's Columbian Press.
This press, which also depends on a combination of levers, was invented in Philadelphia, in 1814, by Mr. George Clymer of that city. It was introduced into Lon don in 1818, and a manufactory established for making ' them. The construction of this press will be readily understood, from an inspection of the elevation in Fig. 6, where AA is the main frame resembling the letter U. The platen BB, fixed by screws to the bottom of a square pillar P, two opposite angles of which slide in angular grooves in the two pieces of metal a, a, which stretch from the frame, and have adjusting screws, &c. to tighten them to the square pillar.
The mechanism or combination of levers, by which the descent of the platen is produced, is shown at H1KLMN. The main lever LMN moving round a strong bolt at N, passes through a fork in the frame at N. The other end L of the lever passes through an aperture between the vertical bars at m, and its central part at M has a stout pivot or gudgeon cast upon it, which goes into collars at the top of the square pillar P, kept together by strong bolts. Two links L, 1, one being on each side, connect the main IVells's Printing Press.
This press, which has been recently constructed in America by Mr. Wells of Hartford, has been described by the late Professor Fisher. See Fig. 8. The plates, draw ing, and description of it, are taken from Ferguson's Lec tures, vol. ii. p. 265. " The frame is of iron, cast (with the exception of the feet) in a single piece ; and is of such form and dimensions as to be incapable of springing while the press is in operation. The platen (4) is of cast. iron, and is of the dimensions of an entire form. The cir cular projection in the middle, with six radiating pieces, gives it an ample degree of firmness. The platen is im mediately acted on by bringing nearly into a straight line the two main levers (6) and (17 ) These levers, in presses of the medium size, are fifteen inches each in length, and in the position represented in the figure, which is that of the greatest obliquity, they want two and a quarter inches at their point of contact of being straight. The lower end of each lever is four inches broad, and is rounded off into a portion of a cylindrical surface of half an inch radius. A piece of steel fixed within the circular projection in the middle of the platen has a hollow bush or bed of corres ponding figure ; in this the lower end of the lever (17) is set. The upper end of this lever is hollowed out in the same manner to receive the lower end of(6), and the upper end of (6) to receive a projection from the under side of the top of the frame. At (5) there is a provision for rais ing or lowering this projection by slips of sheet iron or tin, and thus adjusting the position of the levers to the best working state. The ends of the levers and the beds in which they rest are overlaid with steel, and the beds are so con trived as permanently to retain a small quantity of oil. (9) is a spindle of wrought iron, fastened at the upper end by a screw and nut to the shorter arm of the balance lever (7), and branching below into three parts, each of which is attached by an adjusting screw to the platen. This answers the double purpose of keeping the platen steady, and enabling the weight (18) attached to the longer arm of the lever (7) to lift the platen and carry back the bar im mediately after each pull. The platen is still farther guided by lateral projections which run in grooves con nected with the cheeks of the press.