(3) A press with double levers.
(4) A gyrating or sliding press.
(5) The roller press used by Herr Andre.
(6) And the press of Herr Steiner in Vienna.
Herr Müller in Karlsruhe and Herr Ackermann in London have a press with paper cylinders the construction of which is unknown to me.
IV
THE LEVER PRESS
This was the first press that I used with advantage, and it is used still in Munich in all important establishments for work that demands speed particularly. It would be an excellent printing-machine in all respects if it did not have the defect that its power cannot be increased much more than six hundredweight without forcing the workmen to undue exertions. Therefore it is no longer available for large plates or for works that require immense power. It is very good for pen designs not larger than a letter-sheet, and two workmen, one to ink-in and the other to print, can produce twelve hundred impressions in a day without hardship.
The pressure is produced by a lever six to twelve feet long, fastened to the scraper below and to a spring (an elastic board) above. It is connected with a tread, and when forced down, presses with the desired force on the scraper and so on the plate. The board holding the lever overhead must be partially movable like a spring because the lever describes a part of a circle on the plate below. Hence the pressure at the beginning and end of the impression is not so great as in the middle, and great care in choice of wood and manufacture is demanded to give the spring board the necessary elasticity and power combined. I have found a board of young dried pine the best, the dimensions being six feet long, eight inches wide, and two inches thick, provided that the fibres all ran lengthwise. It is not always possible to find a good board at once. Often I have found that the difference between two boards made a great difference in the effectiveness of two presses otherwise exactly the same.
The scraper arm consists of two parts, of which the shorter one, to which the scraper is fastened with a screw, is only one and one quarter feet long. The other part is as long as the height of the press permits. The higher a lever press is, the better is it, because then the circular motion described by the scraper wood approaches a straight line more and more, so that the press exercises a more uniform pressure during all stages of the impression and is easier to handle. The second illustration shows this kind of press in the moment when the impression has been finished, the printing-frame opened, and the scraper arm swung back again.