Finishing and post-press
Finishing questions check that you can plan the sequence cutting, folding, binding, laminating and die-cutting so tolerances do not accumulate, and that you know the tolerance each operation can hold.
Cutting and creasing
- Guillotine work needs correct clamp pressure, a true back gauge and a fresh cutting stick; cut the largest dimension first and check squareness with a diagonal measurement, typically to within 0.5 mm.
- Die-cutting uses cutting rules around 23.8 mm high and lower creasing rules with a matrix in a platen press; make-ready is impression adjustment until cuts nick cleanly and creases fold without cracking.
Folding and binding
- Parallel folds suit leaflets, right-angle folds build sections; score coated stock above roughly 170 g/m2 and fold with the grain to prevent cracking.
- Saddle stitching suits roughly 8 to 64 pages depending on stock and requires creep compensation; perfect binding mills and notches the spine and glues it, and needs a minimum spine width for the title.
- PUR gives lay-flat behaviour and better grip on coated stock; wire-o and spiral need extra gutter allowance, commonly 5 to 8 mm.
Laminating and packaging
- BOPP film of 15 to 25 micrometres, matt or gloss; delamination usually comes from too low a roller temperature, too little pressure, or an ink or coating the adhesive cannot key to.
- Folding cartons: crease lines must run parallel to the grain. Corrugated board is stiff in one direction only, so design the box to take compression along the flutes.
Worked example
A 32pp saddle-stitched booklet on 120 g/m2 stock, calliper 0.11 mm, is one section of eight nested sheets. Each sheet sits inside the previous one, so its head trim shifts by one calliper and the innermost sheet creeps 7 x 0.11 = 0.77 mm. Compensate by shingling, stepping each sheet 0.11 mm inward in the imposition, or split the job into two 16pp sections, which halves creep to 0.33 mm.
Traps that cost marks
- Folding against the grain on heavy coated stock and then treating the cracking as an ink fault.
- Ignoring creep until the inner pages show visibly narrower margins.
- Trimming after binding when the imposition assumed trimming flat sheets before folding.