FIG. 152.—_Diagram of Applegath and Cowper’s Perfecting Machine._ ]
FIG. 153.—_Cowper’s Double Cylinder Machine._ ]
Fig. 152 is a similar diagram, to show the action of the double or perfecting printing machine, in which the sheets are printed on both sides. It will be observed that the general arrangement of impression cylinder, rollers, &c., is represented in duplicate, but reversed in direction. There are also two cylinders, B B, the purpose of which, as may be gathered from an inspection of the diagram, is to reverse the sheets of paper, so that after one side has been printed under the cylinder, E´, the blank surface may be turned downward, ready to receive the impression from the form, A B. Fig. 153 gives a view of the Cowper and Applegath double machine, as actually constructed. The man standing up is called the _feeder_ or _layer-on_. He pushes the sheets forward, one by one, towards the tapes, which carry them down the farther side of the more distant cylinder, under which they pass, receiving the impression; and so on in the manner already indicated in the diagram, Fig. 152, until finally they reach a point where, released by the separation of the two sets of tapes, they are received by the _taker-off_ (the boy who is represented seated on the stool), and are placed by him on a table. The bed or table which carries the form moves alternately right and left, impelled by a pinion acting in a rack beneath it, in such a manner that the direction of the table’s motion is changed at the proper moment, while the driving pulley continues to revolve always in the same direction. The movements of the table and of the cylinders are performed in exact harmony with each other, for these pieces are so connected by trains of wheels and rack-work that the sheets of paper may always receive the impression in the proper position as regards the margins, and therefore, when the sheets are printed on both sides, the impressions will be exactly opposite to each other. This gives what is technically called “true register,” and as this cannot be secured unless the paper travels over both cylinders at precisely the same rate, these are finished with great care by turning their surfaces in a lathe to exactly the same diameter. The action of the machine will not be fully understood without a glance at the arrangement of the endless tapes which carry the paper on its journey. The course of these may be followed in Fig. 154, and a simple inspection of the diagram will render a tedious description unnecessary.