Mastering the fine art of sharpening metal blades

ALBANY — The basics of knife-sharpening haven’t changed in thousands of years. But today’s metals can make it a challenge.

When I first heard the admonition, “A dull knife is a dangerous knife,” I was determined to master the art of sharpening a metal blade. As a literal and figurative “tenderfoot,” I learned to judiciously use a whetstone to keep a keen edge on knife and axe so that either could slice paper and shave the limited hairs my preteen arms had to spare.

For those unbelievers out there, the admonition is true. The majority of self-inflicted cuts I’ve received have come when my knife slipped while butchering game, carving wood or cutting lines. One of the reasons for this phenomenon is that a dull knife requires more force to be used while cutting than a sharper knife would. This greater pressure increases the chance of slippage or lack of control over the blade. Whereas a sharp knife uses the wedge geometry of the blade to make the cut without relying on force. The blade glides through materials with little effort and is easier to control in regard to the direction and depth of a cut.

My first sharpening experiences were with blades made of carbon steel, which is relatively soft and has been the primary material for knives and other cutting tools for centuries. In an effort to create blades that retain a sharp edge for a longer period of time many modern knives are made of various steel alloys, which create a “harder” steel. However, all blades have one thing in common regardless of the materials they are constructed from — they will all get dull.

The knifemakers’ art is akin to wizardry in that the steel must be soft enough for the maker to craft and shape the blade but hard enough to retain a sharp working edge. Therefore, makers strive to achieve a balance between strength and hardness in the blades they craft. Strength prevents a blade from breaking, while hardness affects its ability to hold an edge. Hardness is measured on a Rockwell hardness tester with most knife blades being in the mid-50s to low-60s on the Rockwell C scale. Most 440 C knife blades come in on a Rockwell C scale of between 58 to 60.

Whereas I could sharpen my older style carbon steel blades in a short period of time, I found myself taking an hour or more to achieve less satisfactory results on my first stainless blades. My earliest sharpening tools were a series of whetstones. These stones are made from natural sedentary stone and use water as a lubricant. Stones come in a variety of Grit sizes:

• Coarse grits: For repairing damaged edges or for very dull knives;

• Medium grits: For general sharpening;

• Fine grits: For refining and polishing an edge;

• Extra fine grits: For achieving a razor-sharp edge.

The condition of the blade being sharpened dictates which grits are used. In a perfect world, a blade should never be dulled to the point that coarse and medium grits are required. To prevent this, knives and other cutting tools should be sharpened periodically while being used to retain a finished edge. Think of the stereotypical depiction of a butcher frequently stopping to use a steel to ensure his blade retains a razor-sharp edge.

Synthetic whetstones are now available with superior cutting materials and a more consistent grit size increasing their performance. Today, diamond whetstones are now available at affordable prices. They are known for their durability as well as the ability to sharpen very hard materials. This makes sharpening 440 and other alloys much easier.

Another factor critical to the sharpening process is maintaining the correct angle between the edge of the blade and the sharpening medium. A variety of guides and systems are available to ensure the proper angle is maintained. This becomes more important with harder steel where more passes on the stone are required.

Over the years, I have had the opportunity to observe and interview a number of custom blade-makers and pick their brains on sharpening techniques:

• Sharpen the blade to the appropriate angle or relief for the task it was designed for, i.e. carving, skinning, butchering;

• Use stones, rods or other abrasives that are hard enough to efficiently remove the steel being worked;

• Use a series of abrasives in a graduation from coarse to fine ensuring a smooth final grind;

• Work one side of the blade until a “burr” is created then work the other side (some systems will sharpen both edges at once);

• Remove the burr with a leather strop.

When it comes to the sharpness of a blade, a frequent comparison is the edge of a surgeon’s scalpel. A number of years ago, I watched professional blade sharpener Phil Comiskey sharpen a variety of surgical instruments. Comiskey used a series of small belt sanders. With 17 years worth of experience, he did not use a guide, relying instead on a steady hand and delicate touch as he passed the blade’s edge across the abrasive belt. The belt moved at a speed that made my hand-sharpening efforts laughable. However, it did not move so fast that the friction between blade and belt overheated the blade, damaging its temper.

Today, a variety of belt grinding/sharpening systems are readily available to anyone seeking the ultimate edge on their cutting, carving tools. Regardless of the sharpening system, select the universal goal to create a safe and efficient cutting edge. The 1860’s slogan for IXL knives brings the point home: “My IXL cuts real well. But when she slips, she cuts like hell.”