Offset lithography is the most popular commercial printing because printers using it produce results quickly and cheaply. Other processes work better in specific situations, while lithography performs best for the most jobs. Lithography products good results because plates carry sharp images. Its plates are easy to make allow to run at high speed, so this process is fast and low price.
- knowing how offset presses work means you can plan jobs to take advantages of different machines and avoid expensive problems.
- Familiar with presses makes you judge good service and be on the schedule.
- Printers very in the types, sizes and abilities of the presses in their shops.
- Customer who understand the limitations and advantages of various presses make good choice between printers to economy and quality
Feeding and register units
The feeding and register units of a sheetfed press take 1 sheet of paper at a time and position it ready for printing. Good register requires that each sheet enter the printing units from precisely the same position. the feeding and register requites that each sheet enter the printing units from precisely the same position. The feeding and register units of small, inexpensive presses may very the position of each sheet by a much as 1/16″. Largely, costly presses may have register to tolerances close to 1/1000. Perfect registration is difficult for a machine running 3 sheets per second.
Paper small presses goes in shortest dimensions 1st. For instance, on an 8/5″ x 11″ sheet, the 8.5 size is the gripper edge. Large presses take paper the wide way. For example, a 35″ press take a 23″ X 35″ sheet, with the 35″ side providing the gripper edge. Gripper hold tightly to about 3/8″ of paper, forming a strip that cannot receive ink.
With large presses, the griper edge is usually no problem because paper is almost always trimmed or cut up after printing. However, small presses usually run stock cut exactly to 8.5″ x 11″ or A4, 11″ x 17″ or A3.