Learn To Sharpen
Learn To Sharpen Your Own Knives At Home
With a little practice and some acquired skills, you can learn to sharpen your own knives, and experience the thrill of making a blade shaving sharp!
Professional Quality Knife Sharpening-
Sharpening is a precise, repeatable process to bring the edge of your knife to the keenest possible apex. Hopefully, hair shaving sharp or better. Some think sharpening a custom knife is an art form or some sorcery handed down from wizard to apprentice. I believe that my knife sharpening service is a science-based skill learned through trial and error and can therefore be understood by anyone who desires to do so. This first article familiarizes us with some common terminology and practices, so we can be on the same page while communicating.
Sharpening a blade is bringing the two sides, or "cheeks," of the knife together by grinding or honing away steel evenly from either side to create an "apex." The objective is to finish this apex to the finest, narrowest "edge width" you can. In well-sharpened knives, that edge width is below one micron. A micron is approximately forty-MILLIONTHS of an inch, so while it sounds simple, the process requires high precision!
Multiple tools and systems are available to sharpen a custom knife professionally, but only one WAY to sharpen it. That is, the two bevels of the blade must be ground with stones or sandpaper in such a way as to bring them together and create an APEX, with as small an edge width as possible, in a fine, straight line, with no burrs. The "grinding" is where multiple tools and styles come into play.
Sharpening By Hand-
The old, tried, and accurate method of sharpening, hand sharpening, involves using stones or other abrasives to grind and shape the bevels in a progression from coarse to fine grit stones. Typically this style is purely by feel and requires many hours of practice to develop the skills and muscle memory to achieve repetitive success. A good tip is to mark the edge of your knife(JUST the edge) with a black magic marker or sharpie. Then gently rub the blade on the stone while adjusting the angle till you erase all the marker with the stone. This will tell you you're on the edge bevel. Additionally, it is hard to know the angle being applied to the blade. Many sharpeners follow the rise already there, whether right or wrong. As a machinist, I like quantifiable, measurable, REPEATABLE results and sharpening knives to the angle appropriate for the steel and their job. Read on below...
Fixed angle tools-
Several sharpening aids set the angle between the blade and the stone and keep it constant during sharpening. They include Edge Pro, Wicked Edge, Hapstone, KME, and Lansky. Some use hand power, and some are motorized belts and wheels, but all set a fixed angle and hold it more or less steady. I DO NOT care for the powered models, and here's why: It has been proven through edge retention testing that motorized sharpening of knives is detrimental to the edge retention of a knife steel. It is probably due to overheating the edge on a microscopic level that cannot be recognized with the unaided eye.
Here is an in-depth article by Dr. Larrin Thomas about power grinding edges.
I use a Hapstone fixed-angle hand sharpener because it's mechanically solid, easy to use, and didn't break the bank when I purchased it. I also bought a complete set of diamond stones from 80 to 2000 grit and some finer natural and synthetic stones. Diamond stones remove material, including hard carbides, much faster than natural or artificial stones. For my use, speed, the accuracy of the angle, and the final finish are the most critical factors. Sometimes, I still freehand sharpen my pocket knife, but YOUR knife will get the best edge I can offer. That requires precision, and a fixed-angle HAND sharpener is the way to go.
When I finish the edge on a custom knife, I HAND SHARPEN to an angle appropriate for the regular use of the blade. A 12-15 degree per side angle is perfect for a kitchen slicer made of quality steel, but it is way too thin for a hard-use survival knife. For this reason, I like to have the ability to set the angle and hold it steady through the entire process. Once the bevels are set and symmetrical, I always hand-sharpen a tiny micro bevel at a slightly steeper angle to offer more strength to the edge. For example, if I've set that "primary" bevel at 12 degrees, I'll hand sharpen a 14 or 15-degree micro bevel to finish the edge.
Types of Bevels
There are several ways to professionally sharpen or create the edge on a custom handmade chef knife or Outdoor Knife, and each has advantages and disadvantages. Some are very specialized, while others are pretty common. As you can see in the picture of different bevel types, they vary significantly in the way the blade is brought to an "apex" or the actual cutting edge of the blade. I won't discuss all these, but I think a few more common ones deserve mention. Remember that the picture exaggerates the features of each grind, and we are only looking at the last several thousandths of the blade, usually 1/8 inch or less.
This is the most common way to produce an apex in most US knives, particularly for custom kitchen cutlery. At lower sharpening angles (12 -15 degrees per side), it can have an extremely keen edge capable of slicing hard veggies without breaking them. The disadvantage is that there is minimal "thickness behind the edge" to support the apex and prevent rolling and chipping. Therefore, the maker must select a robust and tough steel to support these thin, keen edges. At higher angles(18-25 degrees per side), this type of edge can become a capable "hard-use" knife. Your custom knife maker can assist you in choosing the steel for your bespoke knife!
Convex edges serve several purposes on blades, most often seen and recognized on axes, hatchets, and hard-use bushcraft knives. They function well on these blades by allowing more steel behind the edge for better support and strength. Some folks believe this edge also helps food release in the kitchen, with the convex curve tending to push the food away from the blade's flat. Maybe an experiment is to verify this claim!
Compound (double) bevel-
This is the grind I modify slightly and use on all kitchen and low-impact knives. Essentially I sharpen the blade to shaving sharp at the appropriate angle for the knife's purpose, then raise the pitch one or two degrees and hand sharpen with light strokes to create a "micro-bevel," honed to 3000 grit. This allows for a little more steel to support the edge and helps ensure the edge is clean and deburred. After a light stropping with .25 micron diamond paste on smooth leather, this is my favorite edge for kitchen use and my EDC. It is exactly the edge I will put on your blades too!
Hollow Ground Bevel- Another highly common grind is the hollow grind. As the image above shows, the hollow thins the steel dramatically behind the edge, allowing for a keener edge. It can produce a fine edge on a thick, heavy use outdoor knife or something as delicate and precise as a straight razor. Several "factory" makers employ hollow grinds so they can use slightly thicker blade material and still have a crisp edge. In my opinion, this helps reduce warranty claims for breakage.
Chisel (single) Bevel-
In the West, this grind is mainly seen in woodworking chisels, planer blades, etc. However, the Japanese regularly make kitchen cutlery with a chisel grind. It is important to note that such a knife must be made with respect for the "handedness" of the end user. A knife chisel ground for a right-handed person will not perform as well for a lefty, and vice versa.
How to Sharpen-
Now I'll tell you how I put the final sharpening on a Handmade Knife or YOUR knife. It involves a combination of wet, slow belt grinding to set the initial angle of the edge or "secondary bevel" and a final hand refinement of the "micro-bevel" apex with the Hapstone Hand Sharpener and a series of bonded diamond stones, seen in the picture above.
For the initial setting of the secondary bevel, I use my Reeder Grinder with the knife sharpening attachment. I can easily set the angle within a half degree with this attachment, and the accuracy pays off! I also use a Kool Mist, which delivers a cooling and lubricating fluid and compressed air to the point of contact between the knife and belt to keep the edge from overheating and becoming brittle. Again, this sets the angle of the secondary bevel and merely roughs out the profile of that, saving time for me and money for you.
Then it's on to the Hapstone for hand finishing, where the edge angle can also be precisely controlled. I use a progression of diamond, and natural stones to hand sharpen, refine, and finish the final edge to 3000 grit, remove the inevitable burrs, and polish. So again, running through a progression of diamond stones from coarse (80 grit) to excellent (3000 grit), I refine the edge, raising and removing a burr at each determination. Even at 80 grit, the blade is shaving sharp, and each subsequent step only refines and polishes the edge.
From there, it's to a denim strop loaded with Flitz chrome polishing compound for a few strokes to refine the edge further. The final step is a strip of top-grain cowhide glued to a flattened 1x4 board and charged with 1-micron diamond spray. Here the rim gets a few more strokes to ensure burr removal. Final inspection under 20x magnification guarantees a keen burr-free edge from butt to tip, and testing with the Edge on Up sharpness tester assures a super sharp, high-quality edge. (Click HERE to see me using the sharpness tester in real life!)
Notes and Tips for Freehand Sharpening--
Sharpening by hand, or freehand sharpening, takes practice. Don't get frustrated if it takes hours or days to learn! Follow these tips for a head start:
1) I suggest again that you use a felt tip pen to color the edge bevel of your knife before you start. This will help you "find" that edge as you hone or sharpen your blade.
2) Concentrate on holding the angle steady as you stroke the knife across the stone, first one side, then the other, in EDGE Leading passes.
Notes and Tips On Stropping-
My strops are glued to 1x4 boards, and I primarily use only two.
The first is a denim strop loaded with Flitz chrome polish. This step requires only 3-5 strokes per side to remove the bulk of the burrs left from sharpening (if you deburred with your stones). It also polishes the bevel and apex, creating a micro convex at the peak.
I follow the denim strop with a top grain leather strop(smooth side out), charged with a 1-micron diamond compound consisting of sifted and screened 1-micron diamond chips in a carrier of water or alcohol and designed to remove light scratches and burrs. Again, 3-5 strokes per side are needed to remove all traces of burrs and add some final polish to the bevels.
Keith Nix Knives sharpening services are available to individuals and businesses in Asheville, Weaverville, Swannanoa, Black Mountain, Old Fort, Marion, and greater Western NC.
We'll follow up soon with more of the Learn To Sharpen Series!
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Photo Credit: ZKnives.com