Offset plans: inks, passes and keeping items together

An offset run prints a few forms (plate sets), each a fixed number of times. The run chooses which items share a form, how many copies of each item sit on it, and how many sheets each form runs, so every item stays within its overrun at the lowest cost. Three choices change that plan: whether an item may be split across forms, which items may share a form, and how the form's inks fit the press.

Keeping an item on one form#

By default an item may be split: part of its quantity on one form and the rest on another, when that saves sheets or money. The job's Splitting items across forms setting chooses how splits are treated:

• Allow (the default) splits an item across forms whenever that saves sheets or money.
• Avoid plans both ways. A plan that splits an item ranks first only when it saves more than the job's minimum saving (5 % by default, 0 to 50 %).
• Never plans only groupings that keep every item whole.

Each item can also be set on its own to Keep together (always on exactly one form), to Allow, or to Job default. See Keeping items together.

When no plan within the job's forms and overrun keeps the kept items whole, the run says so, names the items that would have to split, and offers the best plan that splits them, marked as breaking keep-together, so you can choose it knowingly. That plan is searched only while enough of the run's time limit is left.

On digital sheets, keep-together depends on the method. True shape and Strips plan repeated forms: each form is printed several times, and each kept item sits on one form. Every item that fits the sheet gets a plan: at worst one form per item. True shape keeps at most 40 items per gang group together this way. N-up builds whole plans with each kept item on one form. Rolls print one continuous layout, so keep-together doesn't apply to them.

Which items may share a form#

Ganging rules split the items into groups (for example by stock or coating). Each group is laid out on its own forms, so no form mixes groups. Keep apart and Due within stop particular items from meeting on one form. If the groups need more forms than the job allows, the run stops at once and says how many groups there are ("These items form 3 gang groups but the job allows 2 forms").

Inks, units and passes#

When an offset job has a press (its own or the team's default offset press) and at least one item's inks are known, every form is costed with the inks it needs. Item inks come from the files or are entered by hand (see Item inks: detected and declared).

An item's Coating property, when it names a coating (for example "Gloss UV"), replaces the flood coating found in its file. Two varnishes of different finishes (gloss and matte) need two units. Two names for what may be one ink (PMS 185 and PMS 185 C) are counted separately, so a form never looks cheaper than it is; a run note points them out, and entering the same name makes them one ink.

An item whose inks are unknown, next to items whose inks are known, is counted as CMYK on each printed side, and a run note says so. When no item's inks are known, or the job has no press, ink limits aren't checked.

Passes#

A pass is one trip of the sheets through the press.

The job's Work style can force straight passes on a convertible press (Single-sided or Sheetwise); Auto uses the press's perfecting. Work-and-turn and Work-and-tumble aren't available yet.

The ink limit#

• Fit the press (the Default on offset): ganging never adds a pass. A form may need no more passes than its neediest item needs on its own, so an item that needs 2 passes anyway can take other items along in those 2 passes.
• Allow extra passes: forms may need up to the press's Max passes (1 to 4), and every pass is costed. For each number of forms the run keeps a plan with extra passes only when it costs less than the best plan that fits the press.
• Warn only and Off plan without the limit, but forms are still costed with their plates and passes.

An item that needs more passes on its own than the press's Max passes still runs; a run note says so.

Fit the press and Allow extra passes also respect what the press can apply. A coater that only floods a whole side can't coat part of a sheet, so a form never mixes items with different coatings on that side (a gloss and a matte varnish differ, and so do a coated and an uncoated item). An item whose coating or foil the press can't apply at all (no coater of its type and no flood coating from a printing unit, or no cold foil unit) stops the run: choose another press or set the limit to Warn only. When no plan fits, the message says whether it was the ink limit ("allow more forms or passes"), the overrun, or the number of forms.

What a form costs#

The sheets printed are the good sheets, plus the job's Makeready sheets for every pass and the press's makeready sheets per plate for every plate, with spoilage added, rounded up. Impressions are the passes times the good sheets plus makeready, with spoilage, rounded up. A form's cost adds up:

• the paper: sheets printed × the sheet cost;
• the plates, each at the price of whoever makes the job's plates (see Offset press runs), plus the press's makeready per plate time;
• the press's makeready per pass time for every pass, and the impressions at the press's hourly cost ÷ its speed;
• the press's custom ink charge for every ink on the form that isn't one of its house inks;
• the job's Extra cost per form.

Forms then run in the order that washes the fewest units between them (an ink entering a unit is one wash-up; house inks stay loaded). The count is approximate (shown as ≈), and the wash-ups × the press's wash-up per ink change time are added to the plan's cost.

Example#

Postcard A and Postcard B (4 × 6 in) print CMYK; Flyer C (5 × 7 in) prints CMYK + PMS 185 C and Flyer D CMYK + PMS 286 C. They run on a 5-unit straight press, with a 28 × 40 in sheet, ⅛ in bleed, ⅜ in margins, up to 3 forms, 10 % overrun, 150 makeready sheets per pass, 2 % spoilage, $0.25 a sheet, $30 a plate, $60 makeready per pass and $0.018 an impression (no wash-up or custom ink charges). Planned with Allow extra passes (2 at most):

The single form needs 6 inks (2 passes, 6 plates, 612 sheets printed); the two forms keep the spot colours apart (1 pass each, 10 plates). Short runs favour fewer plates, long runs fewer impressions. With Fit the press, PMS 185 C and PMS 286 C always stay on separate forms, because each flyer fits the press in one pass on its own: the short run then costs $577.05.

Over and Under per item#

On an offset job, each item may carry its own Over and Under %, next to it in the item list; an item without them uses the job's Overrun % and Underrun %. The planner keeps every item between its own lowest and highest count, so an item at 0 % / 0 % gets exactly its quantity. See Item properties.

Fixed stations#

On a die the form isn't laid out: every station holds one piece of an item that fits its single-up, unmirrored and with the grain, so a form is a count of slots per kind of station. A die with several kinds (a combination die) fills each kind on the same sheets, so its lower bound is the largest of the kinds' needs, not their sum. A die run may use as many forms as Max forms allows; when the items need more forms than allowed ("needs at least 4 forms") it stops at once. After the forms are chosen, the run lengths are solved exactly. With Fill empty stations on, empty stations are filled with extra copies of an item on that form (or another item whose inks the form already prints) only within an explicit Over %; stations still empty are die-cut blank. Every plan is checked: each piece within 0.25 mm of its station, one piece per station, the station's kind accepting the item. See Standing dies and new tooling.