Before we get to the offset printing machine let's first understand what is offset printing all about. In offset printing, the image or text that is to be printed needs to be transferred from a metal plate to a rubber blanket which is mounted on heavy iron rollers. This roller is one of the most important parts of the offset printing machine as it is that component of the machine which does the printing. "Offset" is a technical term which is meant to convey the process by which the image is transferred from the metal plate to the rubber blanket and thereafter, to the substrate or surface which is the final printing medium, which could be a book, a magazine, a newspaper, or any other printing medium.
Going a little deeper into the functioning of an offset printing machine, it's important to note how the image transfer happens flawlessly with no spillage of ink on the non-printing areas of the substrate. It is known as the offset lithography process wherein the part of the substrate to be printed, draws the ink from the ink rollers while the rest of the substrate draws a soluble film from the water roller that keeps the ink away from the non-printing areas. The main components in an offset printing machine are the ink rollers, water rollers, plate roller or cylinder, offset roller or cylinder and the blanket or impression roller.
There are two types of offset printing machines - sheet-fed machines and web offset machines. In a sheet-fed machine, single sheets of paper are fed into the machine with the help of an automated suction bar which uses mechanical registration for consistency of printing. These machines are perfect for short-run jobs like magazines, brochures, catalogs, etc. On the other hand, the term web offset has nothing to do with the WWW (World Wide Web); the term web offset was coined when WWW was not even in existence. Web in offset printing machines refers to the huge roll of paper that is fitted on the machine to feed the paper into the machine in a continuous stream. Such machines are perfect for bulk printing jobs like newspapers.