(8) On the outer side of the frame there are four wooden strips that can be adjusted as desired. One serves to show the point where the impression is to begin. Another shows where it is to end. Both must be so strong that they can resist the scraper. The other two are adjusted at the sides and guide the scraper.
V
THE CYLINDER PRESSES
When Herr Professor Mitterer installed a lithographic institution for the Feyertags-Schule, the lever press appeared to him to demand too much labor, especially when powerful pressures were desired. He invented the so-called Cylinder or Star Press, which has its place in most establishments, especially those in other countries. It has had minor changes made in it by many persons, but on the whole, nobody has succeeded in improving it notably, except for a considerable improvement made by Herr Mitterer himself. My description will include this improvement.
The cylinder press might almost be called a reversed lever press. Herr Mitterer borrowed from it the idea of effecting the impression with a scraper, but he did not let it move over the plate, as in the lever press. He gave the scraper a fixed, immovable position while the stone was drawn through underneath, thus making his press resemble a copper-plate printing-press somewhat.
Illustration number 4 shows this machine in the moment when the impression has been made. In the middle of the machine is a cylinder ten to twelve inches thick and as long as the breadth of the press. It has strong iron spindles that revolve in well-lubricated brass bearings. Above the cylinder is a board on which is fastened the stone with the printing-frame. The scraper is on a strong lever that is held up by a counterpoise. When everything is ready for printing, the scraper is forced down. By means of a strong iron hook it engages the treadle and thus can be pulled down with the utmost tension. Then the cylinder is turned by means of two levers affixed to the crank, and this draws the stone and printing-frame through under the scraper. One workman alone can do this under ordinary pressure, but an appliance at the other end of the press enables a second workman to help.
VI
GYRATING SCRAPER AND DOUBLE LEVER PRESSES
I have already mentioned the gyrating scraper press. I have improved it considerably. It has the form of the ordinary lever press, but all the parts can be much lighter. For instance, the lever is only one and a half inches thick. The spring (the elastic board) is very elastic and need exert a pressure of only one hundred pounds. The little scraper is only an inch long and presses on the plate with a force of fifty pounds. The press is useful for very thin stones that might crack under greater pressure. The pressure, nevertheless, is great, because it is all exerted on such a small area. The press has two defects. It is easy to miss many parts of the design with the small scraper, and the paper is likely to stick to the leather, producing poor register. I have obviated these faults with the following invention: A large scraper is fastened to the lever to press on the plate with a force of one hundred pounds. A small one is fastened to this in such a manner that it can be moved to and fro easily. While one workman rubs to and fro with the small scraper, another draws the entire stone and printing-frame slowly along under the large one. If good underlays are used in addition, this process will produce beautiful work that cannot be produced so well with any other machine. However, a large field is left in this form for improvement.
The fact that the concentric motion produced by a single lever can be transformed into an almost straight motion by use of a second lever, led me to design a double lever press, which has turned out very successful, giving great force with speed. As its description would demand much space, and since on the whole it ranks equally with the improved cylinder press, I offer to send models to those who desire to have everything useful for the art.