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Knife Sharpening Techniques: The Basics

Knife Sharpening Techniques: The Basics

The sharpening of cutting tools, from crude stone spearheads to fancy knives and swords, has been practiced and perfected by humans for thousands of years. It’s only in recent human history that sharpening techniques, abrasives, materials, and equipment have radically improved, along with steel quality and variation.

While opinions and preferences on knife sharpening techniques can vary from person to person, everyone should be familiar with the following basics and include them in their knife sharpening process:

  1. Select the Proper Abrasive & Coarseness
  2. Find Your Angle
  3. Select Type of Stone Lubricant
  4. Establish A Burr
  5. Refine the Edge
  6. Fully Deburr & Strop

1. Select the Proper Abrasive & Coarseness

For softer steels, more bargain friendly and less wear resistant abrasives will work fine. For harder super steels, using diamond, cubic boron nitride (CBN), or quality ceramic abrasives are best. If it’s your first time sharpening a knife, selecting a coarse stone to start will allow you to more quickly profile the edge and set the bevel. Most factory edges are done by hand on a powered belt or grinding wheel. This leaves substantial variations in angle that need to be evened out and profiled with your first abrasive. For knives that have already been profiled, you can generally start with a medium to fine grit stone, depending on the condition of the edge. A coarse stone will only be needed to fix damage to the apex, such as a chip or severe roll, or to quickly bring back a very dull knife.

2. Find Your Angle

One of the more crucial steps in knife sharpening is finding or establishing your angle. There are three basic options: match the existing angle, reprofile to a higher or lower angle, or add a microbevel. Which you choose is up to you but may take into account certain factors, such as the knife’s intended use or how much time and effort you want to spend.

Match the Existing Angle: When matching the existing angle as closely as possible, there are several methods, and your choice may depend on personal preference or whether you are sharpening freehand or with a guided system. Two reliable methods when freehanding are to simply go by feel or to start with the knife at a low angle and tip it upward, slowing increasing the angle until the shadow just under the bevel disappears. A tried and true method for freehand and guided sharpening is to cover the bevel with permanent marker and adjust your angle until you are completely removing the marker. This will be difficult if sharpening a factory edge, due to the inherent angle variation of most factory bevels. All you can do it get it as close as possible and then proceed with profiling the entire knife to that angle, until everything is evened out.

Reprofile to A Higher or Lower Angle: If you choose to reprofile a knife to a higher or lower angle, it will generally take more time and effort than matching the existing one. Choosing a lower angle will widen the bevel, increase cutting performance, and extend edge retention. It will, however, provide less stability to the apex and increase the possibility of sustaining damage, such as a chipped or rolled edge. The sharpening process involves removing steel from the bevel’s shoulder, until it’s completely apexed at the new, lower angle. Choosing a higher angle, on the other hand, will narrow the bevel, provide more stability to the apex, and decrease the risk of sustaining edge damage. It will, however, decrease cutting performance and edge retention. The sharpening process involves removing steel from the very edge or apex at the new higher angle, until it is ground back far enough to encompass the entire bevel.

Add A Microbevel: Alternatively, if significantly grinding the edge back is not desirable, or time is of the essence, simply adding a microbevel at a higher angle is a great option. It is not only quick to establish and touch-up without hardly removing any steel, but it also adds the positives of a more obtuse angle (i.e., edge stability and less risk of damage), while still maintaining many positive attributes of an acute one (i.e., increased edge retention and cutting performance).

Any of the above options (lower angle, higher angle, or microbevel) can be accomplished either through look, feel and experience, or more accurately with the aid of a digital bevel gauge, also known as an angle cube.

 3. Select Type of Stone Lubricant

Which stone lubricant you use is largely personal preference. That said, some stones have particular ones that should or shouldn’t be used. So, be sure to check the product page or manual to see what the manufacturer recommends. The most common options are water, water with a drop of dish soap, honing oil, mineral oil, lapping fluid, and dry. Certain stones are porous and will need to be soaked in water before use, others do not. Some sharpeners add a small amount of dish soap to carry away swarf and reduce stone loading. A benefit of oil is that it will not evaporate and need regular reapplication like water. Certain diamond and CBN stones can be used dry, but this tends to speed up loading and wear.

4. Establish A Burr

Once an angle and lubricant has been chosen, it’s time to start sharpening and forming a burr on both sides of the knife. A burr is a raised, thin strip of metal at the very apex that protrudes and curves around to the opposite side of the knife from which you are sharpening. The goal on your first stone is to form a burr along the entire length of the blade, at which time you know you’re ready to flip it over and sharpen the other side until a burr is also formed. Once you have done so on both sides, you can be confident your knife’s edge has been fully apexed and is ready for refining. A burr can often be difficult to see by the untrained eye, and there are several methods for confirming if one has been properly formed. They include using a flashlight, cotton ball, fingertip, or fingernail.

Flashlight Method: Shine a light from the spine of the knife towards the edge. The light will catch and reflect back from the burr, as seen in the below picture. It will appear as a thin, shiny wire along the edge. If a full burr has not been formed, there will be dark spots or gaps in the burr that do not reflect light.

Cotton Ball Method: Gently drag a cotton ball across the burr side of the edge. If there is a burr, it will catch and pull away strands of cotton. The only downside to this method is it may not pick up on any tiny areas without a burr.

Fingertip Method: Gently rub your fingertip perpendicular across the burr side of the edge. A burr will be noticeably rough and catch your skin.

Fingernail Method: Carefully run the edge of your fingernail in a perpendicular direction down the bevel until it meets the apex. If there is a burr, your nail should catch on it. Once hooked onto the burr, you can run your nail along the entire edge. It will slip off any areas without a burr.

If you’re using a guided system, sharpening will likely involve back and forth scrubbing strokes with a 1” x 6” or 1” x 4” stone, moving in a slight sweeping motion to ensure even grinding on both straight and curved portions of the blade until a burr is formed. If you’re freehand sharpening on larger whetstones, it will involve locking your wrists and using sound technique to hold a consistent angle until a burr is formed on each side of the knife. If you’re interested in more details on the different methods, tips, and tricks of sharpening with a guided system or freehand, the internet has a plethora of great instructional videos to learn from.

5. Refine the Edge

Once fully apexed at the lower grit, the edge will still be very rough and unrefined, like a microscopic saw blade. Working through a full progression of stones (e.g., coarse, medium, fine, and extra-fine) will not only refine the scratch pattern but the apex itself, increasing sharpness and cutting ability. Which grit you finish with is largely personal preference. In general however, stopping between 600 and 1,000 grit will yield a more aggressive, toothy edge. Most find this effective for general slicing and cutting materials such as rope, tape, and cardboard. Finishing higher than 1,000 grit will yield a more polished, refined edge, usually preferred for push cutting, shaving and whittling.

6. Fully Deburr and Strop

While it’s a good practice to deburr at the end of each stone, it’s absolutely crucial at the very end of the sharpening process to achieve maximum sharpness. Deburring with a stone is generally accomplished with alternating finishing passes. There’s no exact sequence, but a good example would be finishing with five passes on each side, then three, two, and one. Whether you use into or away from the edge passes is personal preference as well. Each has its pros and cons and is often the subject of friendly sharpening debate. Into the edge, however, has less risk of leaving a wire edge or micro burr on the apex.

Finally, a fantastic way to finish and ensure maximum sharpness with no remaining burr is to strop. Popular choices for strop material are cowhide, kangaroo leather, balsa, and basswood. Even using denim, cardboard, or rolled up newspaper can be quite effective. Stropping can be done on the bare material or after applying an abrasive compound to speed up the polishing and deburring. Stropping should only be performed using away from the edge passes. If using multiple strops and compounds, be sure to clean the edge between strops to avoid cross-contaminating higher grit strops with lower grit particles.

 

Once fully deburred and finished with alternating passes, the sharpening process should be complete. An easy way to then test the sharpness of the knife and ensure there are no dull spots is via the paper test. It should be able to cleanly slice printer paper without getting caught on any part of the edge. The thinner the paper, the harder it is to cut cleanly. For example, after regular paper, you can try magazine paper and finally phone book and receipt paper. If you can cut them all cleanly, rest assured your sharpening session was successful and your knife extremely sharp.

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