Heavy platens are of exceptional strength built to meet the exacting demands of high grade printing. The frame is cast in one solid piece and the platen is placed on finished rails. The move ment of the platen is known as the "rocking-sliding" action due to the platen having on its underside semi-circular rails which work on the rails on the frame and is controlled by a cam known as a "swan's neck." The platen is connected with the back of the frame by two arms, the ends on the platen side working in eccen trics. As the machine works the platen is brought into action with a rocking motion until it reaches a perpendicular position and is then pulled into contact with the forme by a "slide up" or parallel movement.
A cylindrical inking system is a feature of this class of machine. The ink from the duct is fed on to a series of rollers, and oscillat ing metal drum. This ensures a better distribution and also enables a graduated supply of ink to be conveyed to the forme by four inking rollers. It is on this style of machine that the best half-tone and colour work is printed. The machines are built for large sheets (the usual size being about 22 by 14), and are fed and operated in the same way as light platens. The average production from a heavy platen is approximately about i,000 impressions per hour.
The drum cylinder, the successor to Koenig's machine (181I ), is now but little used. The cylinder, continually revolving, makes one revolution for each impression. One half of the cylinder is lower to allow for the return of the type bed which has a short travel. When the cylinder completes its travel the gripper auto matically opens and the printed sheet is transferred to a delivery apparatus known as the "flyers." The sheets as they are delivered are placed one on top of the other on a board at the rear of the machine. The inking equipment is what is usually known as the "pyramidical system," the ink duct being placed in front of the cylinder and the ink transferred to the forme by a system of rollers. The sheets are fed in from the top or crown of the cylin der. These machines are made in various sizes, and a production of between 2,000 and 3,00o is a fair average.
The stop cylinder is essentially an English machine, and com monly known as a "Wharfedale." In this class there is a small cylinder, about three quarters of the circumference being used for impression. On both ends of the cylinder pinions are geared into corresponding racks on each side of the type bed. One of the gears on the cylinder "runs loose" and the other is fixed with the teeth on the under portion cut away. This allows for the return of the bed after the sheet has been printed. The carriage is supported by "bowls" running on rails and receives its reciprocating motion by means of racks fixed on the underside of the carriage geared into large wheels running on bearers and in gears. These are connected by a rod to another set of gear wheels which obtain their motion from small pinions keyed on to the -driving shaft.
The cylinder is rotated by means of racks fixed on the side of the bed. As the carriage is propelled to and fro the gears on the cylinder turn the cylinder and in this way the sheet is printed and is usually fed by hand to lays at the base of the cylinder. When printed it is automatically removed to the delivery board by means of "flyers." The inking system includes an ink trough, or "duct," situated at the back of the machine. From the duct a supply of ink is fed by means of rollers and placed on to a "slab" fixed to the end of the carriage. As the carriage moves to and fro, the ink on the slab is distributed by a group of rollers. The inking rollers (held in brackets behind the cylinder) get their supply of ink from the slab as it passes under them and by this means inking the printing surface. This type of machine is made in a large number of sizes and can run at anything from i,000 to 2,000 impressions an hour.
This machine has been likened to a cylinder machine placed on its end but with the cylinder on which the sheet is placed travelling over the inked forme. The cylinder stops to enable the grippers to take a sheet from the feedboard. The sheets are automatically fed into lays and, after printing, are delivered at the back of the machine. It is a high speed machine capable of printing a sheet 19 in. by 131 in. and producing about 3,00o copies per hour.