Once the printing is complete, the stacks of fully-printed and dried parent sheets are taken to be folded by the folding machine. Each parent sheet zooms through the machine one at a time entering into gates that are set to the proper fold size. A final fold is applied by a heavy arm, called the knife fold, that applies pressure on the fold line. The final project rolls out of the machine as a signature. The majority of projects are folded by these machines, although extremely large projects or those with unique requirements may occasionally be folded by hand.
The folded groups of pages that emerge from the folding machine are called signatures. Most projects have signatures of 16 pages (8 pages on each side of the parent sheet), but projects 6″ x 9″ or smaller may have signatures of 32 pages, and projects larger than 9″ x 12″ may only have 8 pages per signature.