Lithographic Machines.—The hand-press is used for proving and transferring and, in some cases, for printing a job of small numbers. This may be said to be composed of a frame with a roller upon which a movable bed rests, supported by the frame. At the head there is an upright section with a movable bar, actuated by a screw or lever to impart the necessary pressure. The bar is so made that a "scraper" made of boxwood can be fitted into a slot on the underside and secured by a screw. On the end of the bed there is a hinged frame upon which a sheet of metal or leather is stretched. This is called a tympan and is turned down on to the top of the stone, placed on the bed and run through the press under the scraper. It is by this means that an impression is obtained on a press. Small presses are usually operated by hand but the larger sizes are run by power. The method of obtaining a print on a hand-press is to damp the stone, pass a roller charged with ink several times over the surface, and place a sheet of paper on to the stone to marks which determine the position of the print upon the sheet. A few sheets of packing are then placed on the top, the tympan turned down, and the bed containing the stone propelled under the scraper. Thus, an inked impression of the design is made upon the paper. The bed is then returned to its normal position, the tympan raised, the packing removed, and the printed sheet carefully taken from the stone. These various operations have to be repeated for each impression.
Flat-bed.--Flat-bed machines are power driven and are mainly used for printing from stone. They are of a heavy build and comprise a frame held together by cross-stays. Running within the sides of the frame is a bed with racks fixed on the under-side and supported by runners, the machine obtaining its to-and-fro motion by means of a system of gears connected with the main driving shaft. Geared into the upper side of the bed is a cylinder
which is driven by the bed and held in position by brackets. The impression exerted by the cylinder is obtained by springs or levers with weights. The inking apparatus consists of a duct or trough which holds printing ink. This can be regulated by screws and the required quantity of ink supplied by means of a roller to a slab attached to one end of the carriage. As the carriage moves to and fro the ink is distributed by means of a number of rollers. The inking rollers take their supply of ink from the slab and in turn transfer it to the printing surface. At the back of the cylinder there is a damping equipment where water is taken from a trough, transferred to a slab (fixed on the opposite end of the carriage to that of the ink slab), from which the damping rollers obtain a regular supply of water to moisten the stone.
On the crown of the cylinder is a feed-board upon which the paper is placed and from which a feeder takes a single sheet at a time and places it in lays, usually fixed on the inside of the grippers which are connected with the cylinder. As the cylinder rotates it takes the sheet and presses it on to the stone, and in this way an impression of the design is placed upon the paper which is then taken off at the back of the machine either by hand, or by a mechanical device called "flyers." This type of machine is rapidly being superseded by the rotary.
Direct Rotary.—This machine, on which plates only can be used, gives a larger output than a flat-bed stone printing machine. In this type there are two cylinders, one of which carries the plate with the design, the other supplying the pressure. The inking and damping apparatus are so arranged that the plate is auto matically damped and inked as the machine rotates. In this machine the sheet to be printed is placed to lays, fixed on to a bar, which automatically rise as the grippers on the impression cylinder take the sheet from the feed-board to receive the im pression from the plate, the sheet being automatically delivered at the rear of the machine. It is on this class of machine that pictorial posters are usually printed.