Amazing articles on just about every subject...

Printing Presses

( Originally Published 1883 )

Printing-Presses.—The limits of this little manual will not admit of a detailed description of the various presses now in use in book-printing.

We show herewith an old engraving of a sixteenth-century press, and another of Franklin's press. From these to the present newspaper machines, turning out from a roll of paper nearly four miles long 20,000 copies per hour of a newspaper printed and folded, is a long step, and the comparison will convey some idea of the vast amount of study which has been given by inventors in their attempts to perfect the modern press.

For ordinary book work in this country, the press generally in use among printers is the Adams. In this press (see cut), the bed upon which the form of type or plates is placed has no horizontal motion in printing, the impression being taken upon the entire sheet at one upward movement of the bed and form. This press does not print with any great rapidity, and its great advantage lies in the ease with which forms can be " shifted " for ordinary book work.

The Cylinder Press.—When large editions are required, or the book contains wood-cuts, it is usual to employ a cylinder press (see cut), of which there are now in use a great variety.

In these presses, unlike the Adams, the " form " moves horizontally, while the sheet to be printed revolves on the cylinder under which the form of type or plates passes. This cylinder, of course, touches but a small section of the form at once, and by proper making ready," the highest results in printing can be attained upon these presses, while the rate of speed, for book work, is double or triple that of the Adams press.

If it is desirable to still further increase the speed, this is accomplished by the use of the double cylinder machine which, through a most ingenious contrivance of the two cylinders, admits of two sheets being printed at the same time.

Making Ready.-This operation, to which reference 'has already been made, is probably the most important part of press work, as upon its proper execution largely depends the appearance of the printed sheet. The pressman who is able to " make ready " and prepare the " overlays " for fine illustrated work commands a high salary in any printing-office where such work is executed.

All forms require more or less making ready," for even with the utmost care in casting and finishing plates, it is quite impossible to obtain a number of plates whose face and thickness shall be absolutely true. There will be depressions in the plates in some spots where the plate, in printing, seems scarcely to touch the paper, and corresponding elevations in other places. The first impression taken from a form is, therefore, more or less imperfect, and it is the work of the pressman to overcome these irregularities, either by " overlaying " or " underlaying" as may depend upon the character of the press. This process is a very nice one, and it requires no slight amount of judgment upon the part of a pressman to do it effectively. Small pieces of very thin paper are cut and pasted over the low spots either upon the cylinder, or (in the Adams press) underneath the plates. When the impression is too heavy the soft covering of the cylinder is cut away in the proper spot and the pressure equalized throughout the entire form, thus giving an even appearance to all the printed pages.

When, however, wood-cuts appear in the text., the difficulties of " overlaying are greatly increased, and the expert pressman must possess a good deal of artistic judgment to prepare his form so as to produce effectively in the printed sheet the design of the artist and engraver. Few people in examining a finely illustrated book, realize the amount of care required in the pressman to produce such work, and they would be surprised to see the difference between the first impression of the form of cuts and a printed sheet after it is properly " made ready." Indeed, no matter how artistic the work of both designer and engraver, if the pressman fail to understand his business, the result must invariably prove disastrous.

The pressman may, perhaps, devote two or three days to making the " overlays " to a single form of cuts, building up the " blacks," toning down the half tints," or cutting away entirely the " high lights " of the design. This is all done in the general way already explained for the plain text, but of course it requires a thousand times more delicate treatment. Paper about the thickness of tissue is used in making these overlays, and a form of cuts may require hundreds of these small pieces of paper, of every conceivable shape, pasted upon the cylinder before the press can be started for printing.

Hydraulic Pressing.—When the sheets come off the press they are allowed to dry for a time, and are then placed between very hard mill-board, and subjected, in an hydraulic press, to an immense pressure. This does away with the roughness existing on the sheet when it comes off the press ; but if a very glossy surface is desired, it becomes necessary to run the printed sheets through hot steel rollers, called a calendering machine. The book is now ready for the bindery.


Home | More Articles | Email: