Part 18 (2/2)

Most owners of lithographic printeries have tried their hands at inventing presses, but in the end it has always been something based on the sc.r.a.per or the cylinder principle. I myself have made more than twenty designs. Some were very useful and had advantages either in power or convenience, but generally were handicapped by some defect, so that I cannot even say with certainty which was the best of them all. So much depends on the mechanic's execution of one's plans, and a perfect design can be so spoiled by a workman that it is worthless.

I will, however, recount the best that has been done so far for lithography.

In Munich two kinds of stone presses are mostly used. They are:--

(1) The lever press, or, as the workmen generally call it because of its form, the Gallows Press.

(2) The Cylinder or so-called Star Press, the latter term being used because a star-shaped lever is commonly used instead of a crank to turn the rollers.

I have tried and found good the following:--

(3) A press with double levers.

(4) A gyrating or sliding press.

I know also--

(5) The roller press used by Herr Andre.

(6) And the press of Herr Steiner in Vienna.

Herr Muller 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 hards.h.i.+p.

The pressure is produced by a lever six to twelve feet long, fastened to the sc.r.a.per 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 sc.r.a.per 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 sc.r.a.per arm consists of two parts, of which the shorter one, to which the sc.r.a.per 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 sc.r.a.per 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 ill.u.s.tration shows this kind of press in the moment when the impression has been finished, the printing-frame opened, and the sc.r.a.per arm swung back again.

The printing-frame is much like a book-printing frame, and is furnished inside with a second small frame which holds the paper, being furnished with small springs or strings. When the frame has been turned over the stone, the paper must be at least half an inch from the stone to avoid s.m.u.tting, which will occur if it touches. The paper must not touch the stone till pressure is applied, and then only on the spot pressed downward by the sc.r.a.per.

As soon as both parts of the sc.r.a.per arm are in a straight line, so that they form practically one piece, the sc.r.a.per wood is pulled down and the printer draws it toward himself over the printing-frame and the stone plate. At this time the following is to be observed:--

(1) Both parts of the arm must be so fastened to each other that they may be bent like a knee, but once they are straight in line, they must stay in that position. It is well, therefore, so to adjust the parts that they will not be directly over each other, but rather exceed a straight line under pressure, and bend a little inward. The position of the sc.r.a.per must be considered also. On the whole the following rule holds good: the point where both parts are united with a nail or a screw must not be in a perfectly straight line between the point where the sc.r.a.per rests and the point where the arm is fastened above, but should be at least two and a half inches forward of that point. Otherwise the arm may spring outwards toward the workman and injure him severely. The third ill.u.s.tration shows the construction of the sc.r.a.per arm and the sc.r.a.per.

(2) The arm must be grasped as low as possible when being drawn toward one's self, in order to diminish the danger of springing outward.

(3) The workman must press his body tightly to the table of the press to get proper leverage. Standing free, a man of moderate strength could not move the sc.r.a.per at all when the pressure is on, but a man standing in correct position can do it without difficulty.

(4) Under very heavy pressure the inker-in, who stands on the other side of the press, can help by pus.h.i.+ng.

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