Knife Sharpening

TESTING SHARPNESS

To be sure you are improving your sharpening; you need an objective way to test the results. Tests evaluating sharpness range from cutting silk to chopping trees. What you need is a test method that are useful in your workshop as you are sharpening. A major knife maker tests sharpness on nylon paint brushes.

Most people test an edge by rubbing their thumb lightly across the edge and feeling how the edge grabs as it tries to cut into the thumb pad. To keep your thumb calibrated, test a known sharp edge like a new razor blade periodically.

Shaving hair on your hand or arm is another common sharpness test. Shaving sharpness can be achieved even on heavy hunting knives or an axe. I own a hunting knife that will shave even though the edge angle is a rather blunt 30 degrees. I use the term shaving sharp to describe this degree of sharpness and razor sharp to describe even greater sharpness. Razor sharpness is comparable to a razor blade and will litreally pop the hairs off your hand or arm. Razor sharpness is only possible with both a polished edge and a small edge angle.

Testing by shaving can be misleading if the blade has a burr or wire edge. Steel naturally forms a burr - a thin bendable projection on the edge - during the sharpening process. A blade with a burr will shave but will not stand up to hard use. To test for a burr, slide your fingertips lightly from the side of the blade over the edge. You will feel the burr drag against your fingers. Test from both sides, because burrs are usually bent over one way or the other. As your sharpening improves you will be looking for smaller and smaller burrs.

The glint along this edge means a dull blade.

Many good sharpeners, have learned to see a dull edge. Hold the blade in front of you with the edge in line with a bright light. Move the blade around a bit. A dull edge will reflect a glint. Nicks and burrs will also cause glints. When the blade is sharp these glints will be gone.

Another test for sharpness is to press the edge lightly on your thumbnail at about a 30-degree angle. If it cuts into your nail it is sharp. If it slips it is dull. The sharper the blade, the smaller you can make the angle before it slips. Try this with a new razor blade to see how a really sharp blade feels. The down side of thumbnail testing is that the little cuts in your nail get dirty and look bad until the nail grows out. For this reason some people do this test using a plastic pen or pencil.

The only affordable tool I know of for edge testing is the Edge Tester from Razor Edge Systems. The Edge Tester evaluates edges on a 100 point scale for sharpness and smoothness. The principle is similar to the thumbnail test, but the Edge Tester has a special material and shape for repeatable testing. If you're serious about sharp knives, get an Edge Tester.

If you are interested in the sharpness testers used by industry, check out http://www.catra.org/products/CATRATESTEQP.htm

THE EQUIPMENT

SHARPENING STONES

No shop is complete without at least one bench stone, preferably two or more of different grits. I recommend you buy the largest sharpening stones you can afford. Stones for shop use should be as long as the longest knife you plan to sharpen. Smaller stones are handy for field use. Large tool suppliers such as MSC or McMaster-Carr and restaurant suppliers are good sources for sharpening stones.

Natural sharpening stones include both stones found in nature and reconstructed stones. The original stones were quarried natural stones, but now many stones sold are reconstructed. The abrasive material is novaculite, a mineral related to flint and quartz containing mainly silicon dioxide. The relative hardness of novaculite is 6.5 on Mohs scale, just a bit harder than file steel. The original Japanese and Greek waterstones were also from natural sources. Natural abrasives work well on carbon steel knives, but they struggle with harder tool steels and tougher wear-resistent and stainless steels. For modern steels I recommend stones made with manufactured abrasives and industrial diamonds.

Aluminum oxide, which has a relative hardness of 9.2, is also bonded to form reconstructed stones, including modern Japanese water stones (resin bond) and India stones (vitrified bond). Originally this material was from natural sources (emery and corundum), but manufactured abrasives have dominated since the early 1900s.

Ceramic stones are made from alumina (aluminum oxide) or silicon carbide in a ceramic bond. Silicon carbide has a hardness of 9.5 and will sharpen anything except carbide tipped tool bits. Spyderco and others offer ceramic stones in a wide variety of sizes and grits.

Industrial diamonds are made into hones by bonding them to steel and are therefore also called diamond files. Diamond has a relative hardness of 10. Two very different types of diamonds are used in diamond hones. Monocrystalline diamond hones last longer because the diamonds do not fracture readily. Polycrystalline diamond is less expensive.

Diamond hones are made by DMT, Eze-Lap and others. DMT uses monocrystalline diamonds. EdgeCraft's unique answer to bench stones is the Chef'sChoice 400 series diamond file system. It consists of rather thin diamond hones that fit on a magnetic holder. It is a very good value. EdgeCraft has a good pamphlet on sharpening which you can request from the address at the end of this article.

An inexpensive alternative to stones is silicon carbide sandpaper. A piece of silicon carbide (also called wet or dry) sandpaper glued to a wooden block will work as well as a stone. Wet or dry sandpaper on plate glass is popular with woodworkers for sharpening plane irons and chisels, and for flattening the sole of planes. This method is called Scary Sharp by those who promote it.

GUIDES

You will also need a guide to control the sharpening angle. Guides are available for knives, chisels and plane irons. The drawback of most guides is that they waste about 3 inches of stone, so you would need a longer stone. If you mount your stone flush with your work surface, you can utilize the full stone length.

The Razor Edge Guide

The Razor Edge guide clamps on the blade with four Allen screws and I find it inconvenient to use. Also I managed to grind away some of this guide when I tried it on diamond hones. If you find a Buck HoneMaster, buy it. It is a good guide but no longer made.

ROD-GUIDED STONE SYSTEMS

Rod-guided systems have a rod on each stone that slides through a hole in the guide. This controls the angle and also prevents scratching the blade with the stone. Since the guide slides on the rod and not on the stone, a smaller stone is needed. Rod-guided systems sell in the $30 to $50 range, depending on the number and type of stones. A variety of stones are available, including ones for serrated blades. They will sharpen up to a 4 inch blade before you have to move the guide to a new position.

Rod-guided systems are available from Lansky, Gatco, DMT and others. The Lansky has an aluminum guide that goes from 13 to 25 degrees in 4 steps; each angle is 3 to 5 degrees lower than indicated. The GATCO guide is aluminum and reinforced plastic and goes from 17 to 34 degrees in 6 steps, each step is about 6 degrees greater than indicated. I prefer the GATCO to the Lansky because of the GATCO's larger stones and selection of angles. The DMT Aligner guide is all plastic, and goes from 12 to 35 degrees in 7 steps, which are not marked. With DMT hones, which I do not have, the Aligner would be the pick of the litter for this size of system.

The EdgePro Apex Sharpening System

The class act in rod-guided systems is the EdgePro Apex Sharpening System. Ben Dale, the owner of EdgePro, has spared no expense in his pursuit of excellence in hand sharpening. The Apex is rugged and uses relatively large 1 x 6 inch aluminum oxide waterstones. The angle guide is continuously adjustable for any angle from 10 degrees to 35 degrees, with marks at 10, 15, 18, 21 and 25 degrees. My measurements confirmed that the marks were accurate. The Apex comes with a good instruction book.

 

Footnotes:
(1) The Razor Edge Book of Sharpening by John Juranitch
(2) The Complete Guide to Sharpening by Leonard Lee

THE SHARPENING PROCESS

THE COMMON MISTAKES

The mistakes commonly made in sharpening are uncontrolled edge angles, failure to establish a new edge, and leaving the edge too rough. The following methods address each of these mistakes.

The keys to success are:

1) Use an angle guide to control the edge angle,

2) Sharpen until you raise a burr, and

3) Hone or polish the edge smooth.

Some instructions refer to the sharpening motion as trying to slice a thin layer or a decal off the stone. This is bad advice, and here's why: most people won't hold a constant angle this way. Every different edge requires that you hold the blade at a different angle when slicing a thin layer. You instinctively raise the blade until you detect the edge working. This is almost a sixth sense, involving both feeling and hearing. The same thing happens when sharpening by hand. The duller the blade becomes the more you raise it more before you can sense the edge working against the stone. This creates larger edge angles as time goes on and the results gradually deteriorate. Skill and practice will overcome this problem, but the sure-fire way is to use a guide to maintain edge angle.

If you do not remove enough metal to create a new edge, you will leave some of the dull edge in place. The easiest way to determine that you have removed enough metal is to grind until you have raised a burr. Steel will naturally form a burr when one bevel is ground until it meets another. You can then remove the burr in the honing process and have a sharp edge every time.

A final honing and polishing will bring the edge to perfection.

THE CONVENTIONAL METHOD

For fast removal of the old edge, start with a coarse, fast cutting stone. Diamond stones are the fastest cutting manual stones, with Japanese waterstones second. The first step is where most of the work is, and you can benefit most from using a power sharpener.

Set the guide and take a light stroke with the stone. Check the angle against the old bevel. If the new scratch pattern is on the back edge of the old bevel, you are lowering the angle. If it is at the edge, the angle is being increased. When the scratch pattern is centreed on the bevel you are duplicating the original angle. Keeping the original angle is a safe strategy until you gain more knowledge.

If you can't see the scratch pattern, try darkening the old bevel with a black felt tip marker, then stroke the stone again. The scratch pattern will stand out against the dark marking.

When the angle is set correctly, grind one side of the blade until you have removed the old edge. Grind until you have raised a burr. The burr will appear on the side opposite the one you are grinding. With experience you will learn how to stop with just a small burr in this step. If you are not sure, grind until you can feel the burr. Then turn the blade over and grind an equal amount off the second side.
Feeling the burrFeeling the burr.

A burr is a natural occurrence in steel when one bevel is ground until it meets another. When I was learning I would show my work to my grandfather, and he would often show me that I had a burr. It seemed sharp, but the burr would bend over and become dull. I tried to avoid ever raising a burr for years after that. As a result I never got anything quite sharp. Now I know that one of the secrets of sharpening is to raise a burr, then hone it away.

Ceramic knives and some very hard steel will not raise a burr. Here again experience will tell you when you have ground enough.

There are three basic strokes when you sharpen - sliding the stone onto the edge, sliding it off the edge, or circular or alternating strokes. At the first stage, any of the three is okay.

For the next step use a medium stone. Its purpose is not so much to remove material as to grind away the scratches made by the first stone. The medium stone should be about twice as fine as the first. If you started with a 180 grit stone, you can use 320 or 360 now. Use circular or alternating strokes until the old scratch pattern is gone. Then do an equal amount of grinding on the second side.

You might still be able to detect a small burr at this stage. Finish with a few light strokes sliding onto the edge to remove the burr. This is where slicing a decal off the stone is an accurate description. The blade should now be sharp with no burr. The edge now has 320 or 360 grit micro-serrations, which is good enough for many uses.

The micro-serrations are providing some of the apparent sharpness now but they will wear and bend. A steel or a touch-up stone will straighten them and bring back the sharpness. Continue to the next step if you want a longer lasting edge.

For the third step use a fine stone, 600 or 800 grit, and hone using only strokes going onto the edge. Alternate sides with every stroke. This will help prevent forming a new burr.

Your edge should now shave. Test it as described above. If there is roughness, go back to the medium stone. If there is no roughness but the edge doesn't have enough bite, continue with the fine stone.

When the blade becomes dull, repeat the medium and fine stones. Only when the blade becomes nicked or damaged will you need to go back to the coarse stone.

A MULTI-BEVEL METHOD

This variation will give you a longer lasting edge than the conventional method described above. The multi-bevel edge that results is similar to the convex edge found on Moran and BlackJack knives and the Trizor edge on Chef'sChoice knives. This method can be adapted to many types of sharpening equipment.

The first step is to grind an initial edge bevel about 5 degrees less than you want your final angle. This is sometimes referred to as pre-sharpening or thinning the blade. You will put a little more work into this step, but you will save some work later. Grind until the old edge is removed. As described above, the proof is that you have raised a burr.

Now change to a medium stone and set your guide for a few degrees greater angle. On a clamp-on type guide you increase the angle by moving the guide closer to the edge. On a rod type systems you can easily select another angle. Other systems have different ways to adjust the angle. See the section below for a method using the Lansky sharpener.

When you get to the fine stone increase the angle again another couple of degrees. Hone with strokes going onto the edge and alternate sides with every stroke. You are now grinding only a small area right at the edge, removing the burr and the scratches from the medium stone.

Since a finer stone cuts more slowly, it usually takes quite a bit of work to remove the previous step's scratches. By increasing the angle by a couple of degrees when you change stones, you focus this work on a smaller area near the edge and reduce the work needed

HONING

You can further improve the edge by honing the edge on an ultra fine Japanese, Arkansas or ceramic stone, 1000 grit or better. Maintain the same angle as the final step above.

USING OILS AND WATER ON STONES

In North America we usually use oil on sharpening stones; in the rest of the world they use water. Tests by John Juranitch show that because oil carries the dross against the edge, better results are obtained with a dry stone. However, natural stones tend to clog without oil. I prefer ceramic and diamond stones used dry, and my second choice is Japanese waterstones.

I'll leave this up to your personal preference, with the following guidance. With India and bonded Arkansas stones you can use oil or use them dry. Clean them with paint thinner. Use and clean Japanese waterstones only with water, but store them dry and soak them before using. Ceramic and diamond stones can be used dry or with water. Clean them with water and scouring powder when necessary. Washita and natural Arkansas stones can be used with oil, water or dry, and cleaned accordingly.

If you have used water on a stone and want to change to oil, let it dry thoroughly, and then oil it. Once you have used oil on a stone, it is difficult to change back.

 

KNIFE STEELS

Traditionally knife blades are made from steel, an alloy of iron with carbon and other elements. The steels used in knives are called high carbon steels and typically have a carbon content of 0.5 to 1%. This steel in its unhardened or tempered state is easy to shape by forging or grinding. It can then be heat-treated to hardnesses suitable for knives. High carbon steel takes an excellent edge, but it has no corrosion resistance.

Most knives today are made from some form of stainless steel. Stainless steel is made by adding 12% or more chromium to the alloy. It is a little harder to work with and sharpen, but it has the advantage of corrosion resistance. Because of this, it will hold an edge longer in wet conditions. The term surgical stainless steel is meaningless, because there is more than one stainless steel used for surgical instruments. Other elements added to steel to improve hardness, toughness and wear resistance are cobalt, manganese, molybdenum, nickel and vanadium.

The most popular stainless steels in use today are the 420 and 440 families. A typical kitchen knife will be made from one of these steels or a close relative. They are easy to sharpen and have moderately good edge retention. 440C is an excellent compromise of price and performance and is used by many custom and production makers. 440C is slightly more difficult to sharpen than the others, but has better edge retention.

If you buy specialty cutlery or a custom made knife you will have more steels to choose from. ATS-34 is used by custom makers and by a few production makers, notably Benchmade. Among steels, CPM-440V is the edge retention champion, but it is difficult to sharpen. BG-42 challenges CPM-440V in edge retention, and is as easy to sharpen as 440C. Only a few custom makers are using CPM-440V and BG-42 at this time.

Powdered metal technology makes it possible to incorporate higher percentages of alloying elements than will stay in solution in molten steel. Increasing desirable elements like carbon and vanadium has created a whole new family of steels like CPM-440V mentioned above. CPM stands for Crucible Particle Metallurgy, and CPM is the pioneer in this area. Look for new knives to be produced with steels that start with CPM and end with a V.

Steel is heat treated to control its hardness. Steel hardness is measured on a Rockwell hardness tester. Knife blades may vary from about 55 to 62 on the Rockwell C scale. Blades over 60 Rc are difficult to sharpen and chip easily.

Using combinations of tempering and annealing, the maker tries to get the perfect balance between hardness and strength. You want enough hardness for wear resistance without being brittle. Cryogenic treatment, freezing with liquid nitrogen, is used to quickly complete any further transitions in the steel that would normally take place over time, creating a more stable blade.

Sometimes differential heat-treating is used to combine a hard edge with a tough spine. Mechanical methods can be used to create this same effect. Laminated steel with a hard core that becomes the edge and tough outer layers is available in both regular and stainless. The samurai sword is a well-known example of both differential heat treatment and mechanical layering.

Laminated steel is different than Damascus steel. Laminated steel has all the layers parallel to the edge for strength and hardness. Damascus steel has the layers at various angles, and is often chosen for decorative effect.

Another approach to knife steels has been taken by knifemaker David Boye. His knives are made from cast stainless steel. His steel has a matrix of carbide dendrites that are exposed to form a micro-saw when sharpened. These carbides are highly wear resistant.

The search for edge retention led knifemakers to try the wear resistant materials like Vascowear. It is used in industrial knives subject to high wear. Vascowear is a high vanadium steel that has great wear resistance.

Another wear resistant material is Stellite, a cobalt alloy with about 30% chromium, 3% or less iron and 1 to 3% of other elements. Since it contains so little iron, it is technically not steel but a cobalt-chromium alloy. Stellite tests at a low Rockwell C hardness, about 38 to 40, but it contains harder carbides that do the cutting and retain the edge. Stellite will tie or beat CPM-440V for edge-retention, but it is very difficult to sharpen. A cobalt-chromium-tungsten alloy named Talonite is similar to Stellite. Both alloys cannot be heat-treated and are non-magnetic.

Titanium is known mainly for making lightweight, high-strength fasteners for aerospace use, but it is also used for knife blades. Titanium is favoured for salt water diving because of its excellent corrosion resistance. Like Stellite and Talonite, titanium has a low Rockwell C hardness, but it has good wear resistance and requires diamond hones to sharpen. Titanium is also non-magnetic.

Ceramic materials exhibit very high hardness and wear resistance. Boker, Kyocera and others make knives with ceramic blades.

In the future expect to see surface coatings take a greater role in blade technology. It is now possible to coat extremely hard materials like carbides, nitrides ceramics and even diamond onto steel. This can dramatically improve edge retention, and application of these materials to only one side can result in a blade that is self sharpening like a beaver’s tooth. And don’t think the underlying material will always be steel. Carbon and ceramic fibres have some superior characteristics that I would love to see incorporated into knife blades.

The materials used for grinding are measured on another scale intended for minerals. It is called Mohs' scale after its inventor, Friedrich Mohs. The original Mohs' scale runs from 1 for talc to 10 for diamond. Scientists introduced a new Mohs' scale that spreads out the scale between silica and diamond to make it more closely equal to physical hardness, but it never caught on. Because the Mohs and Rockwell scales use different methods they cannot be compared exactly, but knife steel is roughly 5.5 on Mohs' scale and files are roughly 6. A chart at the end of this article compares these scales and the new Mohs' scale.

SHARPENING THEORY
A knife edge knife edge

Several things - blade thickness, blade shape, edge angle, edge thickness and edge smoothness, determine cutting ability.

Blade thickness is set by the manufacturer and has a great effect of slicing ability. Your hunting knife will never slice like a filet knife or a kitchen knife, no matter what you do to the edge. It is possible to change blade thickness a little near the edge, but that can make a big difference in cutting ability.

Blade shape likewise is set when the blade is made and is determined by the usage. For instance, more belly or curve helps skinning and filet knives slice, while a reverse curve is needed on a linoleum knife. Blade shapes like serrations and reverse curves give an aggressive look to fantasy knives.

Serrations help with some cutting chores by letting the edge attack repeatedly from different angles, always slicing the material a different point. This lets you cut with less pressure. In my opinion serrated edges are desirable for three common cutting tasks - slicing tomatoes, slicing bread, and cutting rope. Rescue workers like them for cutting rubber and Kevlar. All other tasks are done as well or better with a plain edge (sometimes called a fine edge). A plain edge is also easier to maintain.

Sharpening is about the remaining three items - edge angle, edge thickness and edge smoothness. Edge angle is measured between the centre of the blade and the bevel or flat cut by the stone. Most Western knives are double bevel, so the total angle at the edge is twice this angle. Asian knives and woodworking tools are single bevel, and the resulting smaller angle can make them aggressive cutters. That is why sashimi knifes seem so sharp.

Edge angles can vary from 10 degrees to 40 degrees, but most are between 15 degrees (filet knives) and 30 degrees (survival knives). Different angles are suited for different tasks. What's suitable in the kitchen will not do for camping. Twenty degrees is about right for kitchen knives, twenty two degrees is good for pocket knives, and twenty five degrees gives a long lasting edge to a camp knife. A good starting point is to duplicate the angle the maker put on the blade. Edge angle is difficult to measure after the fact, but is fairly easy to control when sharpening by controlling the angle between the stone and the blade.

Any edge thickness under a few thousandths of an inch may be considered sharp. Paper is about 2 to 3 thousands thick and will cut you if conditions are right. Edge thickness naturally increases with wear.

Ideally the flats cut by the stone would come together to make a perfect edge with zero edge thickness, but edge thickness is limited by several factors. First is malleability, or the tendency for steel to move when it is pushed. The yield strength of steel is thousands of pounds per square inch, but as the edge thickness approaches zero, it takes only a fraction of an ounce to move it. The force of your hand with a stone or steel can move enough steel to create or smooth a burr.

The second limit to edge thickness is edge smoothness. You can't have a 1/10,000-inch edge if you have scratches 1/1000 inch deep. The grit of the cutting stone determines scratch pattern or smoothness. Good edge smoothness requires careful work with your finest stone.

STROPPING

Stropping the edge to a mirror finish on a leather strop or a buffing wheel charged with a fine abrasive can improve an edge beyond where the hone leaves off. When stropping or buffing you always stroke off the edge to prevent cutting into the strop or buff.

STEELS

A butcher's steel is a round file with the teeth running the long way. They are intended for mild steel knifes that are steeled several times a day, but are not suitable for today's tougher and harder steels. I know a knife shop owner and knifemaker that disagrees, but in my opinion they belong in a knife museum along with natural stones.

A meat packer's steel is a smooth, polished steel rod designed for straightening a turned edge. It is also useful for burnishing a newly finished edge. Because steels have a small diameter they exert high local pressure. Therefore they affect the metal in a knife when used with very little force.

The secret of using a steel is to use an angle about 10 degrees larger than the final honed edge, and use light force. I am not aware of any guide for use with steels. The Raz-R-Steel from Razor's Edge is marked for the proper angle. It's use is similar to crock sticks.

A variation on the steel is the ceramic steel, where the steel rod is replaced by a ceramic one. Since ceramic is an abrasive, it can polish as well as burnish. Ceramic steels are available from many suppliers.

Small ceramic steels are sometimes called zip-zaps. They are available in several grades, and are useful for sharpening serrated knives, or carrying in the field for quick touchups. Ceramic sticks without handles are available very cheaply at pottery shops if you want to make your own. There are people that swear by burned out quartz lamps for sharpening rods. They are textured at about 500 grit, and are harder than natural stones.

POWER SHARPENING MACHINES

While hand sharpening meets the needs of most of us, a machine is the way to get the work done. Here are some power sharpeners worth considering if you do a lot of sharpening.

A wet wheel machine is very useful if you have to remove a lot of material, like re-grinding a broken tip. The water prevents over heating the blade and ruining the temper.

The wet wheel machines mentioned above have a limited number of guides or fixtures available, mostly for planer and joiner knives and other woodworking tools. The only wet wheel grinding system with guides and fixtures for all sharpening needs is the expensive Tormek.

Woodworking catalogs offer a variety of rubberized, nylon and composite buffing wheels for sharpening. These are usually sold industrially for deburring and polishing. They require skill and practice, and they are expensive. I think paper wheels are the best choice for the home knife sharpener.

PAPER WHEELS

If you are comfortable using power tools, try a paper wheel system. Paper wheels are safer than buffing wheels and less likely to catch and throw a knife, but you still work with the wheels moving off the edge, like stropping, for safety.

Most paper wheel sets are 3/4" wide. Koval Knives sells its 1" wide 8" paper wheel set for only $25. Their 6" set is also 1" wide and sells for $20. I also found a cheap 1/2" set made from grey composition board instead of laminated paper. Avoid it, look for the white or brown paper wheels.

I've had good luck with this system. The sharpening wheel raises a burr quickly. The honing wheel polishes the burr off and leaves a mirror finish comparable to stropping by hand. Both operations are done with the wheels moving off the edge for safety.

Using paper wheels requires a little skill, but once you get the hang of it, it is very fast. I sharpen twenty knives at a time for my church's kitchen, and I can do them in less than 30 minutes with this system.

The most difficult knives I ever tried to sharpen was an old set of Gerber kitchen knives. They were so hard that natural stones hardly touched them. Diamonds would grind them, but I don't have a diamond stone fine enough for a shaving edge. Paper wheels is the only system that has ever brought these knives to a razor edge.

I use paper wheels a little differently than recommended by the manufacturer. Normally a grinder wheel turns toward the user, and grinding is done on the front, where debris is thrown downward. The instructions for paper wheels say to use this same rotation but sharpen on top, where debris is thrown toward you. This seems inherently unsafe to me.

Here is how to modify a grinder for safer use of paper wheels.

I recommend you buy a dedicated grinder motor for this purpose. Changing the wheels too often can introduce wobble in them. When you buy a grinder make sure it has removable guards, because you are going to take them off. Put a good light over the grinder so you can see the burr as it develops then polishes away.

Mount the grinder so the top of the wheels moves away from you, and sharpen and hone on top of the wheel with the edge away from you. This lets you see better, and debris or anything caught by the wheel is thrown away from you. Hold the blade level and work near the top for a small angle, down the wheel closer to you for a larger angle.

If you thought trigonometry was something you learned in school but never thought you'd use, think about this. When the blade is horizontal the angle between the blade and the wheel is equal to the angle between the point of contact and vertical (identical triangles). I've marked angles of 0, 15, 20 and 25 degrees on my wheel. I put zero at the top and position the blade at the angle mark I want to grind before I start the motor. Then I turn it on and hold the angle steady as I move the knife lengthwise. Practice a little and you will learn to see the burr and where to hold the blade to get the proper angle.
paper wheels marked with angles

SHARPENING CERAMIC KNIVES

Diamond stones will sharpen a ceramic knife, but you must remove all scratches caused by the diamonds. Scratches act as stress risers and can cause the brittle ceramic blade to fracture.

Silicon carbide wheels or stones can be used to sharpen ceramic knives, which are made of relatively softer aluminum oxide. Since paper wheels use silicon carbide abrasive, they too can sharpen ceramic knives. SC wheels can also remove the scratches from sharpening with diamonds.

Ceramic blades will not raise a burr. You have to use the other tests to determine if you have created a new edge.

Miscellaneous Technical information:

Chef'sChoice
The angles and grits on the Chef'sChoice 110 and 301 machines are as follows:

Stage 1 20 degrees 100 grit
Stage 2 22.5 degrees 200-300 grit
Stage 3 25 degrees 500-700 grit

Thanks to Sam Weiner of EdgeCraft for information and support.

Some other sharpener angles

Normark 20 degrees
Hunter Honer 21 degrees
Byers #1 20 degrees

TABLES:

MOHS HARDNESS SCALE

STONES AND ABRASIVE GRADES - Five Different Systems Compared

TO READ FURTHER:

Woodworking catalogs have lots of sharpening equipment for hand and power tools, and most of it can be used for knives.

The best book on tool sharpening is "The Complete Guide to Sharpening" by Leonard Lee. It has a chapter devoted to sharpening knives.

"Sharpening Basics" by Patrick Spielman covers sharpening knives as well as tools.

Knife making catalogs are good sources of information. Blades N' Stuff, whose catalog was an encyclopedia of knife making, is no longer in business since the death of Bob Engnath, but their information is on the WWW at www.engnath.com

"Step by Step Knifemaking" by David Boye covers sharpening with a belt grinder and buffer, as well as manual sharpening and stropping.