Fig. 18.
Another matter of a similar character and quite as important in its issues is more directly connected with the gripper.
The type of gripper shown in [Fig. 18] is probably the best for general use. It enables the printer to use two or more pins upon which to rest his sheet, according to the particular requirements of his work. Two pins are usually sufficient and answer best, for the following reasons. It is by no means unusual to find that the paper, trimmed though it may be, has slightly convex or concave edges, owing either to insufficient damping or an inaccurate setting of the knife in the guillotine cutting machine. This can, of course, be avoided, but the point at present under consideration is one of possible effects. This contingency and its effect are considerably exaggerated in [Figs. 19A and 19B], but for purposes of illustration the suggestiveness of the two sketches is not at all too emphatic.
Fig. 19.
Start the machine with a light pressure, for once the stone is locked up a certain amount of danger will always exist if at any time it is necessary to reduce the pressure. The stone may still be held by the blocks, even after the bed of the machine has been lowered, only to come down with a snap when pressure is applied. Such a danger might, of course, be averted by slackening the screws and blocks; but then the stone would almost certainly move out of position and the registration of the forme be altered.
Narrow slips of paper folded two or three times, and inserted between the block and the stone, will often check any tendency the latter may have to lift when the screws are tightened.
Of the many annoyances associated with the lithographic machine printer’s work, grit is probably the most troublesome, inasmuch as its presence is almost imperceptible, while its effect is extensive and often disastrous. Its sharp grains become embedded in the inking-roller skins, and plough tiny furrows across the printing forme, doing much damage before the printer realises the presence of any foreign matter on the inking-rollers. Prevention is a simple matter enough, but a cure is rarely, if ever, accomplished. Dust the rollers and examine them carefully before commencing operations, and in this way ensure perfect cleanliness. It may seem a trifle, but it is none the less an important one, and perhaps the reader has already realised that “trifles make perfection, and perfection is no trifle.”