Spine 2.3 mm too wide after a paper change
A 176-page perfect-bound book trims to 148 × 210 mm. The first edition used 80 gsm bulky cream text (bulk 1.60 cm³/g, caliper 0.128 mm per leaf) and a 300 gsm matt art cover (0.30 mm per sheet) with matt lamination; the spine was set at 12 mm and the binder accepted it. The reprint moves to 90 gsm cream (bulk 1.05, caliper 0.0945 mm per leaf) to cut postal weight, and the cover artwork was not changed. The bindery now reports a visibly loose spine with glue squeeze-out at the spine edges, a 2–3 mm wave along the fore-edge of the cover, and cracking at the hinge where the cover was scored. The cover delivery note says long grain; the text paper was ordered short grain so that it would fit the press sheet. Binding is 12-up, notched and side-glued, with 0.8 mm allowed for glue.
1. Calculate the spine width for both editions, stating your assumptions, and list the cover-template changes that follow.
Read the worked answer
Formula Spine = (leaves × caliper) + (2 × cover caliper) + glue allowance. Leaves = 176 ÷ 2 = 88.
First edition
- Text: 80 gsm × 1.60 bulk = 128 µm = 0.128 mm per leaf; 88 × 0.128 = 11.26 mm.
- Cover: 2 × 0.30 = 0.60 mm.
- Glue: 0.8 mm.
- Total: 12.66 mm, so a 13.0 mm spine would have been right; the 12 mm used was about 0.7 mm tight and survived only because a perfect-bound block compresses.
Reprint
- Text: 90 gsm × 1.05 = 94.5 µm = 0.0945 mm; 88 × 0.0945 = 8.32 mm.
- Cover: 0.60 mm. Glue: 0.8 mm.
- Total: 9.72 mm, call it 9.7 mm.
The new spine is 2.3 mm narrower than the 12 mm artwork, which is exactly the visible slack.
Template changes Rebuild the cover from the binding docket, never scale the old file: spine 9.7 mm, total width 2 × 148 + 9.7 + wrap, 3 mm bleed, 5 mm wrap on all three open edges, spine text re-centred on the new width and kept 3 mm clear of both spine folds.
2. Diagnose the loose spine, the fore-edge wave and the hinge cracking, and state what you would specify differently.
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Loose spine and squeeze-out. The cover carries 2.3 mm more spine than the block needs. A perfect binder applies glue and presses the cover against the block; with slack, the cover cannot be pulled tight, the block rotates slightly in the case, glue is forced out at the joints and the spine looks rounded and hollow. Correction: the calculated 9.7 mm spine, confirmed on a bound dummy before artwork is released.
Fore-edge wave. A 300 gsm sheet laminated on one side only is a two-layer composite: the film is a moisture barrier, the paper is not. As the bindery humidity moves, one face responds and the other does not, and the sheet waves across its width. It is worsened by a knife score, which locally compresses the sheet. Correction: condition the stock at 50–55% RH before lamination, use a controlled-tension matt film or a coating applied to both faces, and replace the score with a proper crease on a matrix.
Hinge cracking. Two contributors: the crease cracks the laminate and the coated surface at the hinge, and the text paper was ordered short grain, so its grain runs across the spine. Every opening fights the grain, which loads the hinge joint and stops the book lying flat. Correction: text grain parallel to the spine (long grain for this format) on every edition, crease rather than score, and a breaker pass on the cover.
3. Before the third edition goes to artwork, what must be agreed in writing with the paper merchant and the binder?
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With the merchant
- Caliper and bulk stated as a tolerance, not a nominal: for example bulk 1.05 ± 0.03, caliper measured with a micrometer on a sample from the actual mill lot. At 88 leaves a 3% caliper error is 0.25 mm of spine.
- Grain direction declared on the delivery note and confirmed on the reel or pallet label, with the text paper long grain (parallel to the spine) and the press sheet size adjusted around that, not the other way round.
- Single mill lot for the whole edition; mixing lots is the usual cause of a spine that is right on the dummy and wrong on the run.
- Cover: caliper, coating, and whether the lamination is film or aqueous.
With the binder
- A signed spine-width docket based on a 12-up dummy bound from the actual production paper, approved before the cover file is released.
- The cover template dimensions (spine, wrap, bleed, hinge positions) and a rule that no text sits within 5 mm of a spine fold.
- Creasing method for 300 gsm laminated cover, conditioning requirements, and the acceptable spine tolerance on the finished book (typically ±0.5 mm).
Only then does the designer rebuild the cover: artwork after docket, never docket after artwork.