Choosing a binding structure and fixing the spine width for 512-page registers reprinted yearly

Recommendation: section-sewn (thread) case binding with a hollow back, mull and three tapes, cased in with French joints. The hollow back (hollow tube) lets the case swing clear when the book opens, which is exactly the lie-flat behaviour the cooperative is asking for, while the sewn sections give the page-pull strength a daily-use register needs over five years. Sewn sections also mean the 50-copy reprint is a repeat of a known process rather than a new tooling setup.

Rejections:

• Perfect binding (EVA or PUR). The cooperative's own two-year failure is direct evidence that an adhesive spine on a 512-page A4 block will not survive daily use. PUR would be better than EVA, but it still will not lie flat at a 30 mm spine, and it needs a notching and clamping setup this workshop does not have.
• Wire-o or plastic comb. These lie flat and are cheap and quick, but at 512 pages the block is heavy, the punched holes tear under daily handling, and the register cannot be cased or given the cloth-jointed look the cooperative expects.
• Side stitch or stab binding. Quick, but it will not open flat without a large gutter loss and would hide the inner margin of a register that is written in.

Design points to state in the offer: no rounding and backing, because a flat spine keeps the book open on a desk; tapes rather than cords; headbands optional.

Text block:

• 512 pages ÷ 2 = 256 leaves.
• 256 × 0.10 mm caliper = 25.6 mm of paper.
• Sewing swell for 16-page sections on 80 gsm is about 10–12%: 25.6 × 1.12 = 28.7 mm, say 29 mm.
• Add mull and paper lining ~0.3 mm and three tapes ~0.3 mm: block pressed thickness ≈ 29.5 mm, take 30 mm for setting the casing jig.

Case spine width:

• Spine = block + two boards = 30 + (2 × 2.5) = 35 mm.
• Add covering material allowance, about 1 mm total for 1.2 mm rexine turned over the joint: 36 mm finished spine width.

Boards:

• Height = page height 297 + two squares of 3 mm = 303 mm.
• Width = page width 210 − French joint 8 mm + fore-edge square 3 mm = 205 mm.

Why the joint matters here: a 30 mm block needs a full 8 mm joint; a 5–6 mm joint borrowed from thin-book practice will make the boards bind when the register is opened and will break the covering material at the hinge within months. Also check the millboard grain runs head-to-tail on the board, i.e. vertical when the book stands, so the boards do not bow.

Fix in a signed specification sheet, with a retained dummy copy:

• Paper: 80 gsm cream, caliper 0.10 mm, bulk 1.25 ± 0.02, grain long grain.
• Section size 16 pages, sewing thread type and number of tapes, stitch length.
• Pressed block thickness and the measured swell percentage actually used.
• Board: 2.5 mm millboard, grain direction.
• Case spine width 36 mm and the cover artwork's spine panel width, so the printed spine does not drift onto the boards.
• Covering material: supplier, batch, thickness, turn-in 15 mm.
• Board dimensions 303 × 205 mm and joint 8 mm.

What can change the spine width: a new paper lot with a different bulk is the main risk - 80 gsm paper from another mill can run 0.095–0.11 mm caliper, which over 256 leaves is a 4 mm swing and will make the reprint's case either loose or tight on the same cover template. The same applies if a reprint is produced digitally on a different stock, or if the printer changes the section size and therefore the swell. So the specification must include a clause that each lot is checked with a ten-sheet caliper reading before the cover is printed, and that any change beyond tolerance triggers a revised spine width and a new dummy, rather than a silent adjustment on press. Keep the dummy and one production copy sealed as the reference.