The sharpest knives are those whose cutting edge is down to a very small point. Clearly the sharpest knife would be one with only one molecule of width at the cutting edge. While that “perfect knife” would be very sharp indeed, the edge would be so weak that it would break almost immediately. There are a number of techniques used to prepare and edge to give the best performance. In a cutting application a sharp edge may be the best solution but in a crush cut application that uses pressure to crush the target material, a more durable and rounded edge may be more appropriate. Cutting edges in nature can give us some good guidance when thinking about sharpness. Shark’s teeth and Rat’s teeth, among the sharpest teeth found in nature, are serrated. These serrations allow the tiny serrations in the edge of the tooth to begin the cut more effectively. Sometimes the same can be true of an industrial knife. This depends very significantly on the material being cut and how it is presented to the cutting edge. In one application a very highly polished edge may give the best cut while in another, a rougher surface finish like the shark’s tooth may be the better alternative. Here is a list of some of the edge preparation techniques that can be applied:
- Beveled edges or multiple bevels – the steeper the cutting edge angle, the sharper the knife but the thinner the cross section. The thin cross section makes for a weaker but sharper knife.
- Honing – A specific radius, bevel or profile can be honed onto an edge, especially in crush cut applications to give a more durable and consistent edge to the knife. This gives a less sharp but stronger cutting edge and allows the edge to withstand higher cutting pressures.
- Polishing – A polished edge give a very sharp condition to the edge itself. A highly polished surface or bevel also provides less surface irregularities reducing adhesion and surface friction making for a cleaner cut.