Lay Marks: Press Sheet Orientation and Alignment Guide

Lay marks (also called lay edges, alignment marks, or side guide marks) are reference marks printed in the non-printing margin of a press sheet that indicate the correct paper position on the press bed. They tell the press operator exactly where to place the sheet against the Side Lay and Front Lay guides — the physical stops that position the paper for each impression.

Every offset press has two positioning guides: the Front Lay (or gripper guide) that stops the paper at the correct distance from the printing cylinder, and the Side Lay (or side guide) that stops the paper at the correct distance from the press's lateral reference edge. These guides must be set precisely on the first sheet and maintained throughout the press run. Lay marks verify that the guides haven't drifted and that every sheet is in the correct position.

Lay marks are distinct from registration marks (which verify color-to-color alignment) and crop marks (which indicate where to trim). Lay marks serve a different purpose: they verify that the entire press sheet is correctly positioned on the press bed before printing begins.

Without lay marks, the press operator must rely on visual alignment of the sheet edge against the guides — a process that's prone to error, especially at high speeds. Lay marks provide a precise reference point that eliminates guesswork and reduces make-ready time.

PDF Press generates lay marks automatically based on your sheet size, gripper margin, and side-guide position.

There are three standard types of lay marks, each serving a specific alignment function:

1. Arrow Marks (Lay Arrows): Triangular or arrow-shaped marks that point toward the exact position where the paper edge should align with the lay guide. Arrow marks are the most common and most visible lay mark type. They're typically 8–12 mm long and positioned in the non-printing margin at the front and side lay positions.

The arrow points inward toward the printable area, and its tip indicates the exact alignment position. During make-ready, the press operator adjusts the lay guides until the arrow tips align perfectly with the paper edge. Any gap between the arrow tip and the paper edge indicates misalignment.

2. Line Marks (Lay Lines): Short horizontal or vertical lines (typically 15–20 mm long, 0.5–1.0 pt weight) that indicate the alignment position. Line marks are simpler than arrow marks and are used when the press has automated alignment sensors. The sensor detects the line as a reference edge and adjusts the lay guides automatically.

Line marks are often paired: a solid line for the primary alignment position and a shorter reference line 1 mm inside the trim area to help the sensor distinguish the lay line from the sheet edge.

3. Cross Marks (Lay Crosses): Small + symbols positioned at the intersection of the front lay and side lay guidelines. Cross marks serve as a combined reference point, indicating both the front and side alignment in a single mark. They're positioned at the two corners of the sheet where the lay guides meet — typically front-left and front-right.

Cross marks are less common than arrows and lines but are preferred by some press operators because they provide a single reference point for both front and side alignment, rather than separate points for each axis.

The press bed has two reference guides: the side lay (the guide that stops the paper laterally) and the front lay (the guide that stops the paper longitudinally). Each requires its own lay marks:

Side guide marks: Positioned along the left or right edge of the press sheet (depending on which side the lay guide operates). They indicate where the paper's side edge should align with the side guide. Side guide marks are essential for ensuring that the image is centered laterally on the sheet and that the registration is consistent from side to side.

Side guide position: Most offset presses use a pusher-style side guide that pushes the paper against a fixed stop on one side (typically the operator side). Some presses use a puller-style guide that pulls the paper from the opposite side. The side guide mark must be on the same side as the side guide — if the guide pushes from the left, the mark goes on the left edge.

Front lay marks: Positioned along the gripper edge of the press sheet. They indicate where the paper's front edge should align with the front lay guide. Front lay marks are essential for ensuring that the gripper grabs the paper at the correct position and that the image is centered top-to-bottom on the sheet.

Front lay position: The front lay is always at the gripper edge (the top edge as the paper feeds into the press). Front lay marks are placed in the top margin, typically 10–15 mm from the sheet edge, one at each corner.

In PDF Press, the side guide position can be set to Left or Right, and the front lay position is always at the top (gripper) edge. The engine generates the correct lay marks based on these settings.

The gripper edge (or lead edge) is the front edge of the press sheet that the press grippers grab to feed the paper through the press. The gripper margin — typically 10–15 mm of non-printable space along this edge — serves multiple purposes:

• Physical grip: The press grippers need 8–12 mm of paper to hold securely. This area cannot have printed content because the gripper metal presses into the paper.
• Lay mark position: Front lay marks are placed in the gripper margin, close to the physical edge.
• Gathering marks: Step marks and OMR marks for automated gathering are also placed in the gripper margin.
• Registration targets: The top row of registration marks is often placed in or near the gripper margin.

Gripper edge positioning for lay marks:

• Front lay arrow: centered in the gripper margin, typically 5–8 mm from the sheet edge
• Side guide arrow: at the side of the sheet, in the gripper margin, pointing toward the side guide position
• The gripper margin must be clear of all printed content — only marks, targets, and color bars should appear in this zone

Common gripper margin widths:

• Small-format presses (A3, B3): 8–10 mm
• Medium-format presses (SRA3, B2): 10–12 mm
• Large-format presses (B1, full-size): 12–15 mm
• Web offset: No gripper margin (continuous web), but lay marks are still used for the cut-off position

PDF Press lets you set the gripper margin width and automatically positions all lay marks, gathering marks, and registration targets within the available space.

Not every press run needs all three types of lay marks. Here's when each is appropriate:

Arrow marks: Always recommended. Arrow marks are the most universally useful lay mark type because they're visible to the operator at production speed and provide a clear, unambiguous reference point. Use arrow marks for all offset press runs and any digital press runs that require manual alignment.

Line marks: Use when your press has automated alignment sensors that can detect a line reference. Many modern Heidelberg, Koenig & Bauer, and Komori presses include laser alignment sensors that read lay lines and adjust the guides automatically. If your press has this feature, line marks reduce make-ready time significantly.

Cross marks: Use when you need a combined front-and-side reference point, particularly for presses with a single alignment camera positioned at the sheet corner. Cross marks are also useful for short-run jobs where you want to minimize the number of marks on the sheet.

When you can skip lay marks:

• Digital presses with automated registration (the press uses the sheet edge as reference)
• Proof prints that won't be run on a press
• Jobs where the registration marks alone are sufficient for alignment

Industry standard recommendation: Always include arrow marks at minimum. The cost of printing a few arrows in the margin is negligible, but the cost of a misaligned press run (wasted paper, make-ready time, potential remake) can be significant. See also registration marks and crop marks for the complete marks system.

Adding lay marks to your imposed PDF in PDF Press:

1. Open the Marks panel in the imposition settings and enable Lay Marks.
2. Choose the mark type: Arrow, Line, Cross, or Any combination. PDF Press defaults to Arrow marks for maximum visibility.
3. Set the side guide position: Left or Right. This determines which edge of the sheet receives the side guide marks. Check your press operator's preference — most presses use left-side guides.
4. Set the gripper margin: Enter the width of the gripper margin (8–15 mm). PDF Press positions all front lay marks within this margin.
5. Set the side margin: Enter the width of the side margin (5–10 mm). PDF Press positions all side guide marks within this margin.
6. Configure mark size and weight: Default arrow size is 10 mm, line length 15 mm, line weight 0.5 pt. Customize for your press operator's preference.
7. Add other marks: Combine lay marks with registration marks, crop marks, color bars, and gathering marks as needed.
8. Preview and verify: The live preview shows all lay marks in their correct positions relative to the printable area, gripper margin, and side margin.
9. Export: Generate the imposed PDF with all marks.

PDF Press ensures that lay marks never overlap with other marks in the margin area. If the margin is too narrow for all marks, the engine will warn you and suggest increasing the margin width.