Text 3 Letterpress printing machines

There are four main types of letterpress printing machine. All combine the following elements; inking, printing, feeding and delivering.

The platen press consists of two plane surfaces: the forme constitutes one of these, the blank paper being placed on the opposite surface. The forme is inserted into the machine vertically and locked firmly into place, Ink is picked up by inking rollers from a revolving disc or drum above the machine, and these are then passed across the forme to charge it with ink, While the machine is open, the paper is inserted and the two flat surfaces, which are hinged at the bottom, are brought together under pressure by the press to make the impression (the printed sheet).

On a platen press it is very easy to adjust the impression for different thicknesses of paper and board by altering the distance between the two surfaces, so the machine lends itself to a variety of types of work. Platen presses are normally small (up to A2) and used for jobbing work such as stationery, tickets and small leaflets. Most of this work can now be, and usually is, printed by the process of offset lithography; nevertheless, platen presses are still used for embossing, cutting and creasing and for hot-foil stamping.

The flat-bed cylinder press In this type of press, the forme is held horizontally in the flat-bed while the ink rollers and sheets of paper rotate over it alternately, the paper being held around a cylinder while it is being pressed on to the forme to make the impression.

These presses can print a sheet up to AO size or even larger, and used to be used for printing more substantial work, such as books and magazines.

The rotary press Rotary presses print from a curved or flexible metal or plastic plate. The plate can be produced from a forme — by moulding from it and then making the plate from the mould — or photographically. It is clamped to a cylinder which revolves against another cylinder carrying the paper. The plate cylinder first revolves against ink rollers and then makes an impression on the paper carried on the impression cylinder.

Rotary presses can be sheet-fed or web-fed, and letterpress is still widely used with this latter kind of press.

The advantages of web-fed printing are speed. Web-fed presses therefore lend themselves to long runs. The disadvantages is that the web-fed presses involve a very high initial outlay, need more time before they are ready to start printing and mostly produce only items of a fixed length.

Web-fed rotary letterpress is used for labels, business forms, computer stationery and national newspapers. The technique is used also for a large proportion of mass-market paperback books, with specialized presses printing by letterpress from plastic or, by flexography rubber plates. Sheet-fed rotary letterpress presses are now rare.

The belt press The belt press is a version of the rotary press where flexible relief plates are mounted on two continuous belts that revolve against a web of paper. The belts vary in length depending on the number of pages in the book. The printed pages are cut and folded into four-page units, collated in order, and fed directly into a binding machine, so the process can turn reels of paper into bound books in one operation. However, the belt press can print in only one colour, and the binding has to be unsewn.

These presses are used almost solely for bookwork. The great advantages of belt presses are that they can produce virtually any size of book and lend themselves to short runs, down to two or three thousand copies, enabling the publisher to gear his runs closely to the demands of the market.