The average running speed of a two-revolution press is about one-third greater than that of a stop cylinder, or about eighteen hundred impressions an hour, as against from one thousand to thirteen hundred and fifty impressions from the stop cylinder, this being the comparison in presses of the average size, printing sheets about 33 × 46 inches. The driving power required is in the proportion of about five for the two-revolution press to three for the stop cylinder, and the wear and tear is in about the same proportion.
Another press, which is still employed to a small extent for book-work, is the flat-bed perfecting press. This press is virtually two two-revolution presses combined into one, with the advantage that they require only one man as "feeder," but with the disadvantage that they produce only about two-thirds as much work as two separate single-cylinder, two-revolution presses. Their greatest disadvantage lies in the difficulty of preventing the fresh ink on the side of the sheet first printed from "setting off" on the packing of the cylinder which prints the reverse or second side. Mechanisms are employed to move the "tympan sheet" or outside covering of the second cylinder along at fixed intervals, but they are complicated and troublesome. These presses are expensive and cumbersome, and can generally be used only for inferior grades of work in large editions. Under the care of a skilful and painstaking pressman, good work can be produced from them, but fine book-work is always done on stop-cylinder and two-revolution, single-cylinder presses, which have now been brought to a high state of perfection.
Nearly a hundred years ago Hansard wrote, "The printing machine in its present state appears susceptible of little improvement." He was, in truth, right so far as the main principles of the flat-bed cylinder press are concerned, but there have been immense improvements in many of the details. With the introduction of automatic sheet-feeding devices, and improvements in the driving, inking, and delivery arrangements, mechanical ingenuity seems to have been exhausted. The temptation is strong to apply Hansard's prediction to the flat-bed cylinder press of the present day, but with the many surprises that meet us in other fields this would border on temerity.
Already there have been great advances in adapting the entirely rotary principle to the printing of high-grade work, although its use is still restricted to the production of large editions.
As early as 1852 Hoe & Co. made a rotary press for D. Appleton & Co., especially for printing the famous Webster spelling-book. The types were locked up on the cylinders in curved beds, called "turtles," and the sheets were delivered by a sheet-flier. Probably thirty million copies were printed on this press, which was dismantled nearly twenty-six years ago.
In 1886 this same concern made a press which is still used for printing some of the forms of the Century Magazine. This press had two pairs of cylinders, and curved electrotype plates were used on it. The paper was in a roll at one end, and at the other end there were delivered, to each revolution of the cylinders, eight eight-page signatures already folded to the size of the Century page. This was the first rotary press made for a good grade of book-work. Two similar presses were afterward made for Harper's Weekly and for the Strand Magazine of London.
What is known as the rotary art press was made in 1890 for printing the fine half-tone illustrations in the Century Magazine.
This has one plate cylinder and one impression cylinder, and curved electrotype plates are used. The sheets are "fed" by hand in the usual manner, and are printed on one side at a time and delivered by a sheet-flier. It produces as much work as four flat-bed cylinder presses and of better quality. The plates are inked by sixteen rollers. The performance of this press is another demonstration of the superiority of the rotary over the flat-bed principle of printing.
Since then hundreds of rotary presses have been made for magazine and book printing, most of them equipped with attachments for folding the sheets as they are printed, and all having a high rate of speed. C. B. Cottrell & Co. have made many rotary presses for magazine printing, most of which deliver the sheets flat, without folding, and most of them made to suit some predetermined size or sizes of sheets or pages.
In the evolution of the printing press there are three sharply defined stages: first, the flat impression surface and the flat printing surface, requiring the exertion of all of the impressing power upon the entire surfaces; second, the cylindrical impression surface and the flat printing surface, requiring the exertion of all of the impressing power upon only a narrow line or a small portion of the printing surface; third, a cylindrical impression surface and a cylindrical printing surface, still further reducing the area upon which all the impressing power is exerted.