Making The Cut
When I think about the workings of the bindery, I naturally think about the various machines and systems that are part of finishing. But If I "dig down" to a deeper level, I come to the various components that make up the machines. You know, belts, rollers, and especially...knives. Nothing is more critical to the finished product than the multitudes of knives that are used!
Knives cut and slit, they crease, score, trim, and convert. In short, they're absolutely essential! But few of us realize how high-tech knives are. Take guillotine paper cutters. Large machines are spec'd at 110˝. The knife that is the heart of this machine must be perfectly straight. No "bow" across the width of the main blade, and no variation from one tip of the blade to the other.
Knives are (basically) three different types—regular steel, high-speed steel and carbide steel. The "knife edge" is the cutting instrument, which is welded to the backing insert. And there are the supporting players. The cutting stick (which is typically made from a polymer designed for the knife) is where the blade arrives at the end of its cycle. The "bed knife" is the partner of the shearing knife. Both the manufacture, and the sharpening of knives, is a high-tech art. If you wish to extract maximum life from a three-knife trimmer, or cutter, you will have to have the blades ground to a precise specification on a precision grinding system.
Not many people know that a significant amount of paper dust is generated when paper is cut. In order to minimize this, producing an optimum knife edge is crucial. Kelly Willauer, known in the industry as the "bindery doctor," says; "the proper knife grind can reduce paper dust by 90 percent, and extend the life of a knife by 100 percent."
Further challenges are the materials to be cut. Chipboard can contain a high percentage of metal, and there are papers (mainly imported) which can contain lots of metallic bits and pieces. Obviously, these substrates are going to present a challenge to even the best blades. The grind angle, the control of blade temperature during the grinding process, and other factors, all effect the quality of the knife edge that results. Carbide steel, the king of cutting edges, is also quite brittle, and can easily suffer nicks from things such as un-removed wire stitches.
In a large finishing operation, the sharpening budget can be a major operating cost, so it's the knife life after sharpening that should be watched closely. Not many of us think of knives as being so critical to finishing, but they're essential in your ability to "make the cut."