Crop marks

Crop marks are short hairlines drawn just outside each trim corner, and their only job is to tell whoever is standing at the guillotine exactly where the knife goes. FastImpose draws them from three numbers, all of which you can change:

Taken together those defaults mean every outside trim edge needs 8 mm of clear sheet beyond it — 3 mm of gap plus 5 mm of mark. That figure is worth committing to memory, because it is the number that decides whether a grid which technically fits the sheet is actually printable.

What each number is for

Distance exists so the mark is not printed on the piece. A mark that runs right up to the trim line will, given the ordinary tolerance of a guillotine, sometimes end up on the finished piece as a stray tick in the corner. Three millimetres of clear air is the customary allowance and it is what FastImpose uses.

Length has to be long enough to sight along. Five millimetres is comfortable for a hand-fed guillotine; if you are cutting on a machine with an optical sight or working with a cutter who prefers a longer sighting line, increase it — remembering that every millimetre you add is a millimetre of sheet margin you must also have.

Thickness is a quarter point by default, which is about as fine as a mark can be and still reproduce reliably on a digital press. A heavy mark is worse than a fine one: at 1 pt the operator has to decide which side of the line to cut on, and different operators decide differently.

Why mark distance and bleed must be decided together

This is the part that goes wrong most often, and it is a geometry problem rather than a software one.

Bleed is artwork that extends past the trim so that a slightly inaccurate cut still lands on ink rather than on paper. FastImpose applies a single bleed allowance around the placed page. A mark sits 3 mm outside the trim. If the bleed is 3 mm or more, the mark is drawn on top of the bleed — over the artwork it is supposed to be measured against — and it becomes unreadable exactly where it matters most, in the corners of a dark or busy image.

The relationship to hold in your head is simple: mark distance must exceed the bleed. With the 3 mm default distance, a 3 mm bleed puts the near end of every mark precisely on the outer edge of the bleed, which is the worst possible place for it. Either push the distance out to 4 or 5 mm, or accept a 2 mm bleed. Both are ordinary choices; making neither of them is not.

The bleed also drives the space you need between neighbouring pages, which is a separate calculation with the same flavour. That one is covered on bleed and gutters.

Marks stay true at any scale

The marks are drawn from the sheet transform, not from the placed page. That has a practical consequence worth stating: scaling a page to 65% to fit four-up on A3 does not scale the marks to 65%. A 5 mm mark is 5 mm on the paper at any scale, 0.25 pt is 0.25 pt, and 3 mm of clear air is 3 mm.

This is the behaviour you want, because the guillotine does not scale. The knife has a fixed accuracy in millimetres, and a mark that shrank with the artwork would become useless on precisely the jobs — small, many-up, heavily reduced — where accurate cutting matters most.

What FastImpose does not draw

The setting is a single boolean called crop marks, and it means exactly what it says. There are no other marks in the product:

• No registration marks. There are no colour-separation targets, because nothing here separates colour.
• No fold marks. Booklet mode imposes the fold order but does not print a dashed line at the fold. Fold to the trim marks, or to a made-up dummy.
• No collation marks. There are no stepped spine bars for checking gathered sections.
• No colour bars, no ink strips, no densitometer patches. FastImpose does no colour management of any kind — see format notes.

That is a narrower set of marks than a full press-imposition system offers, and it is worth being clear about rather than vague. For short-run digital work, where the sheet goes to a guillotine and not to a four-colour press with a scanning densitometer, crop marks are the marks anyone actually uses. If your workflow genuinely needs a colour bar, it needs a colour-managed workflow, and that is a different tool.

Common mistakes

Filling the sheet and leaving the marks nowhere

A grid that reaches the sheet edge has no room for marks, so they are clipped or fall off the page entirely. Work backwards instead: subtract 16 mm from each sheet dimension — 8 mm at each end — and solve the grid inside what remains. On A3 that means designing into 281 × 404 mm rather than 297 × 420 mm.

Setting bleed equal to or greater than the mark distance

Three millimetres of bleed against a 3 mm mark distance is the exact configuration that produces unusable corners. Increase the distance or reduce the bleed; the two settings are not independent and cannot be chosen in separate sittings.

Thickening the marks to make them easier to see

A 1 pt mark is 0.35 mm wide and introduces 0.35 mm of ambiguity about where the cut is. If marks are hard to see, the problem is usually contrast or bleed overlap, not weight. Leave the thickness at 0.25 pt.

Marks already baked into the source PDF

If the exported artwork from the layout application already carries its own crop marks, those marks are page content and get placed, scaled and repeated along with everything else — usually somewhere useless, and often overlapping the marks FastImpose draws. Export source pages at trim size with bleed and no marks, and let the imposition add them.

Exporting with marks off and finding out at the guillotine

It happens. Check the corner of sheet 1 in the exported PDF before the job leaves your desk — it takes three seconds and it is the last cheap moment to catch it.