| BackBone Prep |
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| Great page pulls and flexes are always the result of good backbone preparation. Likewise, poor book strength almost always results from poor backbone preparation. Proper backbone preparation exposes the greatest surface area for adhesion. That is, it provides surface area for the adhesive to penetrate or flow around the paper fibers. |
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| Factors Affecting Good Roughing |
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| The amount of backbone roughing needed varies with the type of paper stock. Easy stocks, such as ground wood and free sheets, are full of fibers and need minimal roughing to expose them. More difficult papers require more roughing. These include clay coated or UV-coated sheet and papers containing fillers such as clay, titanium dioxide and calcium carbonate. The more fillers in the sheet, the fewer fibers available for roughing. Another challenge to roughing occurs when machine speeds increase. It becomes more difficult to attain a good rough surface. The grain direction of the paper, whether straight or cross grained, is important to consider for adequate roughing of signatures. Straight grain papers align the fibers parallel to the backbone, and are easier to bond, as the glue has more area to wrap around the horizontally oriented fibers. Cross grain papers become more difficult to bond since the fibers angle perpendicular to the backbone, and only present ends of fibers for the glue to grab. Roughing of cross grain papers becomes particularly important to expose the ends of the fibers. |
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| Roughing Equipment |
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| Roughing methods for perfect binding include circular roughing saw, miller-rougher, sanding disk, rougher-raker, notching and slashing. The standard 48-tooth carbide saw works well on easier papers and some coated papers. A miller-rougher cuts the spine with milling heads that carry additional cutters for roughing the edges of the sheets. On difficult cross grain and coated papers, and on faster moving production lines, a sanding disk with a coarse grit exposes fibers well. A coarse grit is essential because it tears through the paper, leaving more surface area exposed. A fine grit sandpaper, however, smoothes out as it strikes the paper fibers, eventually forming a solid, smooth mass. The fine sandpaper then merely smoothes the backbone surface instead of roughing it. A rougher-raker is also good for difficult stocks and fast production lines. Its specially angled tearing inserts rip out chips, forming a fibrous anchor for the hot melt. |
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| Notchers and Slashers |
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| Notching and slashing increase the gluing area by roughing the surface in a cutting action. This is particularly important when the book is bound cross-grained. A notcher, i.e., a rotary disk with notching units attached, exposes the ends of fibers to provide a large surface area for good glue adhesion. A square notcher tears rectangular pieces from the backbone as the notcher passes through. A triangular or conical carbon bit notcher cuts out a triangular V-shaped notch. The V-shaped notch is particularly effective for exposing fibers when papers of different grains join in the book block. Before notching, the signature must be roughed. You can't make good books with notching only. A sanding disk combined with a notcher is effective on difficult stocks. Some machines mount the notcher on the same wheel with the rougher. Larger machines might include (on the same wheel or interchangeably) a circular saw blade, a notcher, wire teasers and rotary brushes to remove the paper dust. Roughing with a slasher cuts small slashes in the paper to expose a surface area on which to bond. The trick is to expose more fibers by avoiding sharp slashes. The slasher should punch more than cut, as punching and tearing expose more fibers than cutting. A slightly dull slasher exposes more fibers for the glue to bond. Dust removal by brushing and vacuuming is essential to prevent chips of paper from entering the side- or spine-gluing units or the hot melt tank. Otherwise you'll be gluing the dust remaining on the spine rather than gluing the spine itself. Dust collecting in the glue pot will cause foaming in the pot and create char. |
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| When No Roughing Is Needed |
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| Two other adhesive binding methods - notch binding and burst binding - bypass the need for roughing. These methods need little or no backbone preparation because they rough the paper as they cut notches in the signature. Notch binding (perforate binding) cuts notches from the backbone; the adhesive fills the resulting holes and penetrates into the center of the fold. This method roughs as it notches, so needs no roughing. Burst binding (also perforated backbone) needs slight backbone preparation/roughing. In burst binding, it's important to cut off the tabs that remain after punching out the notches, so the glue can penetrate the fibers. Notch and burst binding, by requiring minimal or no roughing, remove less paper from the signature. This allows printing closer to the gutter to realize cost savings for paper. These methods also produce a top quality book. The main point of this discussion: roughing the backbone is essential to prepare the surface for best glue adhesion at the spine that yields strong page pulls and a quality, lasting book. This issue's "Cline's Comments" further discusses getting best adhesion of the spine glue once it is applied to the roughened surface. |
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