Printing presses print an entire set of pages on a single large sheet of paper to make the most efficient use of the paper and to shorten the time required for printing a large number of different pages.
Imposition is the arrangement of the job to be printed on the large press sheet so that after they are printed, folded and trimmed, the resulting pages will back up correctly and be in the proper order.
Work-&-turn and work-&-tumble are both imposition schemes (the layout of the job to be printed on a large sheet-fed litho press). So what are they – and what’s the benefit of using them?
With both, the front or back of the printed piece are printed onto one side of the sheet of paper and the paper is then rotated or flipped to print the other side. This results in the printing of both halves of the sheet and after cutting the printed sheets, the job is done. It requires half the number of impressions that would have been required with standard one-up printing and only one set of printing plates is used, which cuts costs dramatically on jobs that require an equal number of colours to be printed on both sides of the sheet.
The “fronts” of the print job are put on one half of the plate and the “backs” appear on the other half. The sheet is printed, then dried and turned to print the same image again on the other side of the sheet.
In work-&-turn the sheet is rotated 180° and turned over and the gripper edge remains the same. In work-and-tumble the paper is flipped head over heels and the gripper edge changes ends.
The work-and-turn and the work-and-tumble options are economical for several reasons. Using only one plate saves both materials and time. For smaller jobs, step-and-repeat (duplicating) can be used to print multiple images in one pass through the press to save press time.
Imposition was traditionally a manual process of stripping the negatives for each page onto flats. Today it is created electronically using special imposition software and large format imagesetters and platesetters.