Printing and Finishing - The Graphic Design: Reference and Specification - page 143

t y p e s o f o f f s e t l i t h o g r a p h y
Offset lithography is the most widely used method of printing. The process can be broken
down into two basic categories: sheetfed offset and web offset. Print shops are often set
up to specialize in one of these two types of offset printing. Consult the following descrip-
tions for further information on which method is most appropriate for a specific project.

Sheetfed Offset: Individual sheets of
paper pass through the press. Small,
sheetfed presses print on papers smaller
than 18 inches (457.2 mm) in width and
are used for printing fliers, letterheads,
envelopes, and business cards. Larger
presses that accommodate paper sizes
ranging from 19" × 25" (482.6 × 635
mm) to 55" × 78" (1397 × 1981 .2 mm)
allow printers to run larger jobs, such as
posters or book signatures, or gang sever-
al pieces on one sheet. Sheetfed presses
generally work best for small- to mid-size
press runs or when quality is critical.

Web Offset: Paper going through a web
press is fed from a roll and is cut into
sheets after printing. Small-sized web
presses that accommodate paper widths
of up to 9 inches (228.6 mm) are used
for printing business forms and other
small pieces. Larger presses (called
full web presses) that run rolls from 35
inches to 40 inches (889 to 1016 mm)
wide are used for publications. Full web
presses can print sixteen-page signatures
on a trim size that is typically 23" × 35"
(635 mm × 889 mm). Web presses are
designed to print hundreds of impressions
per minute and many thousands per hour
and are suitable for high-volume publica-
tions such as newspapers, magazines,
and catalogs. Many presses also come
equipped with heating units to speed up
ink drying time as well as folding and
binding units to expedite production.

Printers will often gang several pieces on a single sheet,
such as fitting nine 4 1 ⁄ 2 " × 6 1 ⁄ 4 " (114 × 159 mm) invita-
tions on a 23" × 35" (584 × 889 mm) sheet of paper.

Web presses are categorized according to the size of the
paper rolls they run. Small presses called form webs are
used for business forms, while large presses called full
webs are used for publications. In-between sizes include
miniweb, half web, and three-quarter web presses.