This Machine occupies a great part of [Plate 37]. It is represented in [figs. 1 and 2]; the first being an inside view of one of the cheeks; and the second, a view endwise—represented as broken in the middle, to gain space in the [Plate]. As far as possible, both the parts are marked with the same letters.
To begin with [fig. 1], A B C is the cheek: being a kind of shallow box with edges to strengthen it and give it thickness for the steps a b, &c. These steps are strongly fixed to the screws that slide in the boxes A B, and the nuts of which, are seen at c d. The screws enter, besides, into the heads of the perpendicular levers D F, E G, against which these nuts press to set the cylinders, by their steps a b, against the bowl H. This pressure of those cylinders a b is a modified effect: for the levers D F, E G, are drawn inward by the pulling bars I K; which, meeting in the centre of the Machine, are pressed downward by the hanging bar L, to which are suspended the scales and weights M, these being more or less heavy according to the wish of the Printer. It were well to mention a circumstance of some importance connected with this subject:—If the bars I K form together an angle very obtuse, the power of pressure is immense; and the weights at M might be the lighter: But, then, the degrees of pressure at different angles of the bars I K would vary too much, if any excentricity of the cylinders a b, occasioned any motion. It is therefore best to use a sensible angle between the bars I K, together with a weight at M, so much the heavier; by which means these motions will be the more mild and manageable. Proceeding with the description: e f are two hooked screws, by which the pulling bars I K are raised, when necessary, so as to increase the nip in any corner of the Machine, without affecting the rest. It should be observed also, that the steps a b, have dove-tailed slides screwed to them from under the rim, and in it’s thickness, to make them move more correctly, when pressed horizontally by the nuts c d. The upper works of this Printing Machine are not greatly different from those of the common one. In one respect, however, I think them superior. The roller, prepared for the returning blanket, is mounted in a frame g, ([fig. 2]) which moves on a pin in the centre of the Machine, insomuch that one screw and nut h, suffices to regulate this return. This then, is an improvement, as the printer has but one operation to perform instead of two. The use of the piece-roller is the same as usual; and the goods are carried down on stretching bars, &c. exactly in the same manner.
But a more important property of this Machine remains to be noticed, The two cylinders a b, are made to press diametrically across the centre of the bowl H; so that it’s shaft suffers no friction from that pressure. And hence, this two-coloured Machine requires no more power to work it, than a common machine for one colour.
A further property of this Machine deserves attention; but for want of room on the [Plate], we are obliged to describe it by means of dotted lines on the face of the present [figure]. At a b, and at H, we have dotted three toothed wheels, of which one is keyed on each of the mandrels, while the central one is placed in a frame, forming part of a slide N, (fixed on the plate N of [fig. 2]) and by which this wheel is moved up and down at pleasure. Here it is evident, (see again [fig. 1]) that if this central wheel rises, it will turn the mandrel a, backward; and the mandrel b, forward: and this is a peremptory method of increasing or lessening the distance between any two points on the cylinders; or in other words, of fitting the colours of one cylinder into those of the other—an operation which is thus performed by a single movement; while in other machines it is necessary to go on both sides of the machine to produce the same effect. In a word, this process is completed in a few moments, by turning backward or forward a nut like that h, applied to the screw placed against the side of the Machine, as at P Q.
But we have another important property to speak of. The colours on the two cylinders must be fitted in, laterally, as well as longitudinally: and the Machine performs this by an easy method. At each side of the Machine (see [figs. 1 and 2]) is fixed on a centre i, a short lever k l, the bent end of which (l) rises just to the brass step which carries the mandrel of the cylinder a, and is formed so as to push that step inward, when it’s end k is pressed outward; which latter motion is occasioned by the screw m n, which goes all across the Machine, and performs the same office on either side as wanted. This then, is another economy of time and pains; this setting being usually done by passing round the Machine, from one side to the other.
Finally, R S shews one of the cross-bars by which the two cheeks are connected. They are formed as portions of a hollow cylinder, and screwed to the cheeks through flanches, the breadth and form of which give considerable strength to the Machine; which is further strengthened by the bars T V and W X, in it’s upper parts.
In the above description of this Machine, (in which the parts common to other machines are omitted) I have endeavoured to avoid all invidious comparison: and have only said what my additions appear to warrant, and what, I am persuaded they will justify, when this Machine shall be compared with others, placed in the same circumstances for the sake of liberal comparison.