The duties of press operators and their assistants vary according to the size of the printing plant in which they work. Generally, they are involved in all aspects of making the presses ready for a job and monitoring and operating the presses during the print run. Because most presses now are computerized, the work of press operators involves both electronic and manual processes.
In small shops, press operators usually handle all of the tasks associated with running a press, including cleaning and oiling the parts, making minor repairs, and ensuring that printing software is updated and working properly. In larger shops, press operators are aided by assistants who handle most maintenance and cleanup tasks.
Once the press has been inspected and the printing plate arrives from the platemaker, the "makeready" process begins. In this stage, the operators mount the plates into place on the printing surface or cylinder. They mix and match the ink, fill the ink fountains, and adjust the ink flow and dampening systems. They also load the paper, adjust the press to the paper size, feed the paper through the cylinders and, on a web press, adjust the tension controls. When this is done, a proof sheet is run off for the customer's review.
If a digital printing process is being used, most of the aforementioned steps required when printing with plates are automated. The operator receives the customer-approved digital file from the prepress worker and uses computer software to prepare the file for printing.
When the proof has been approved and final adjustments have been made, the press run begins. During the run, press operators constantly check the quality of the printed sheets and make any necessary adjustments. They look to see that the print is clear and properly positioned and that ink is not offsetting (blotting) onto other sheets. If the job involves color, they make sure that the colors line up properly with the images they are assigned to (registration). Operators also monitor the chemical properties of the ink and correct temperatures in the drying chamber, if the press has one.
On a web press, the feeding and tension mechanisms must be continually monitored. If the paper tears or jams, it must be rethreaded. As a roll of paper runs out, a new one must be spliced onto the old one, often at a very fast rate to keep up with the speed of the presses. At such a rate, the press might run through a giant roll of paper several times throughout the hour. In large web printing plants, it takes an entire crew of specialized operators to oversee the process.
Most printing plants now have computerized printing presses equipped with sophisticated instrumentation. Press operators work at a control panel that monitors the printing processes and can adjust each variable automatically.