How do you sharpen a knife?

Question

Just got done sharpening a few knives, and thought it could be useful to post a question about it here.

So lets say I have one of these guys.

With a coarse stone, a medium stone, and a fine stone.

• What is the proper way to sharpen a knife with a stone like this?
• Do I need any other tools?
• Do I need any protective equipment?
• Do I have to use some type of oil?
• Is it better to go fast, or slow?
• Is the procedure different with a knife that has never been sharpened before?
• Do I have to do anything different if the blade has rust on it?
• How do I know when the knife is sharp?

Answer 1

It is very hard to describe knife sharpening in text. I'd recommend searching out a few Youtube videos for tips on technique. That said, I'll add my 2 cents worth. Everyone has a different idea of the "correct" way to sharpen a knife; below is just how I was taught.

What is the proper way to sharpen a knife with a stone like this?

If the knife is already sharp and you're touching up, start with one of the fine stones. If not, start with the coarsest. Work your way from coarser to finer. Put some oil on the stone, put the edge of the knife on the stone at the angle you want (try to match the existing angle), then stroke the knife along the stone as if you're trying to remove a fine shaving of stone. Pull the knife as you do it to sharpen the entire edge.

Do I need any other tools?

No. A jig for keeping the sharpening angle can help, but most likely wouldn't be usable with a stone like this.

Do I need any protective equipment?

No, but be very wary of where your fingers are, and where the edge can go if you slip. Keep your fingers out of that area.

Do I have to use some type of oil?

Yes, to carry away the swarf, or metal particles. For cooking knives I use a vegetable oil. Yes, veggie oil can go rancid, but cooking knives are used and washed often enough that it's not an issue.

Is it better to go fast, or slow?

Slow. I like to take long strokes along the whole edge, concentrating on keeping my angle consistent. I use about a 20 degree angle on kitchen knives.

Is the procedure different with a knife that has never been sharpened before?

Only that you would probably start on a coarser stone.

Do I have to do anything different if the blade has rust on it?

Remove the rust first with fine sandpaper.

How do I know when the knife is sharp?

There are many ways to test. The old newspaper test, where you hold a piece of newsprint in one hand and cut it with the other is a good one. You can try shaving your arm hair until you run out :)

But really, watch some videos and just practice.

Answer 2

I can tell you one thing. In my opinion - sharpening knives very easy to understand but hard to do.

The hardest part is to maintain proper angle when sharpening. Japanese knives like smaller angle, german knives like bigger angle and your hunting knive is even bigger angle.

You need to look for a sharpening system that takes care of angles for you. Here is 2 choices that were recommended to me by knife maker-hobbyist (I'm not affiliated with any of those)

This sharpener system supposed to work very well but I watched video and still wasn't sure I can maintain angle :)

After I got this set - I sharpen knives in no time and I never was able to do it before with just a stone. Angle is perfect. I bought simple set but I got yellow stone later. With yellow stone - it just makes it perfect. I use 17 degree for my Shun knive, I had to make new edge because I think factory is 16 degrees for those. And I use 20 degree for German knives

Answer 3

I like Japanese water stones, which use water as a lubricant. Those look like oil stones, but I'd check with the manual that came with them to see what to use as a lubricant. I'm not familiar with oil stones, but the technique should be the same.

For a knife that has never been sharpened before, (not talking about a new knife here; a commercially-made knife will already be sharpened when you buy it), you'll need to grind an edge on it. That's a bit more involved, basically you need a coarser grit on a moving wheel. This shouldn't be necessary unless you're making knives or restoring a knife that is so dull and rusty it doesn't have an edge anymore.

I think the hardest part is to get the right angle in the first place. Maintaining it isn't so hard once you get used to it. Once you have some experience, you'll be able to tell by the sound and feel of the edge sliding across the stone.

If you place the knife at a shallower angle than the edge, and slowly tilt it to a steeper angle, you can see your oil or water squeeze out from under the edge and form a thin line along the edge just as you reach the correct angle.

Another trick is to run a Sharpie or other permanent marker along the edge. As you remove material, keep checking to see if you're removing all of the black from the edge. If there's still some marker along the "blade side" of the edge, your angle is too steep. If there's still some along the "air side" of the edge, your angle is too shallow.

I usually start with either my coarse or medium stone, depending on how dull the knife is to begin with. I do five strokes on each side, then four, then three, two, and one. If I started with the coarse stone, I move to the medium stone at this point and repeat the process. To see if it's sharp, I use my fingernail. I run my thumbnail perpendicular to the edge of the blade. If it catches, I know it's sharp enough to move on to my finest stone. If not, I do another ten strokes (switching sides between each stroke) on the medium stone and test again.

The fine stone I have is something insane like 20,000 grit. It feels very smooth, and all it really does is polish the edge. It's probably overkill for kitchen knives but it's great for razors and chisels.

Answer 4

A few odds and ends...

Another good test for sharpness of a knife is to hold the edge straight up so you can look along it. With a light above you (a point source of light would be best), look for any reflected light from the edge. A dull knife will show a visible reflection. Only once my knife passes the reflection test do I bother to test cutting paper with it.

For coarse sharpening, I like diamond stones, in two different grits depending on how much sharpening must be done. These are nice because water is a good lubricant. Once I get past that point, I use a ceramic stone to touch up the edge. If the knife is close to being sharp, I'll skip the diamond stones completely.

Of course, always take care when sharpening a knife. Hold the edge in a way so you will not carelessly slice your hands while sharpening.

Answer 5

Sharp tools and knives are a joy to work with and produce better results, faster, and more safely.

The best book on the subject is The Complete Guide to Sharpening. My library has a copy, so check there first.

With good practice, anyone can learn to sharpen well. But you'll need to be able to recognize a sharp edge, correct honing angles, and how long to hone at each step. Developing those skills with tools you're trying to work with is very frustrating. Consider paying someone to sharpen for you to give you something to compare to, and pick one tool or knife to learn on as you go.

I once took my kitchen knives to the grocery store, where the meat department will sharpen for free. They came back sharp but the edges were not straight. There was a wave that I had to grind away before I could sharpen again. Uggh.

Today I take my knives to a sharpening service. He's very good, and it's easy and quick.

Kitchen knives are generally difficult to sharpen because they have a changing-radius curve. Getting the right angle across that is hard. I'm going to write about woodworking tools because kitchen knives are a natural progression after woodworking tools.

If you want to learn to sharpen, probably the easiest blade type is a hand plane. The edge is straight and the iron is size gives you a lot of control. However, the large amount of material also requires more patience. A 1" chisel is the same idea but a bit faster. If you grind the tip on a 6" bench grinder, it will get a concave shape that makes it easier to feel if the blade is on the stone at the right angle. Go slowly so you don't burn the metal. A simple jig helps you get a consistent angle.

To hone blades on a stone without honing your skill, add tools and jigs. For a plane or chisel, there are simple honing gides that give you a consistent angle without too much work.

My friend has a Tormek and loves it. He says that after many years of struggling, he now has sharp tools. There are accessories for just about anything you might want to sharpen. If money is no object, and you're not interested in learning a new skill, this might be the way to go.

Once your knives are sharp, take care to keep them that way. Make sure the food is supported by a surface that is softer than the knife, like a bamboo cutting board. Use a honing steel to touch up the edge often. Avoid pushing a knife through food (like an axe) instead draw it back and forth (like a saw). Don't let the sharp edge bump in to other dishes when washing it. Protect it from rust by drying it quickly and oiling it if you won't use it for a while. Be careful about where you store sharp edges - knives don't belong in drawers.

Answer 6

The way I have always sharpened my knives is to turn an old cup upside down and run the blade across the bottom of it first one side then the other. You will be surprised at how sharp it gets. I learned this from my granny. It's quick, easy and cheap.

The technique can be seen in this video. Turn an old coffee mug upside down and use the unglazed edge of the porcelain

Answer 7

I am a professional, please visit my profile for more information.

To abstract the important points:

1. Keep the sharpening angle constant. I recommend a one to three foot common clamp, or a clamp-style knife guide.
2. Start at roughest and go up 70% of current grit when current finish is uniform around the blade edge.
3. Go slow with no lubricant, faster with common lubricant (your stones); fastest with water-cooled diamond belts.
4. It is highly recommended to finish with some kind of cold, non-toxic polish to ensure microscopic metal dust does not rub off into food. I suggest Flitz.

To Answer your questions

• What is the proper way to sharpen a knife with a stone like this?

These kind are for straight-edge knives no larger than a kitchen knife. Generally, one pushes the knife gently against the stone like they are trying to cut a thin slice of cheese, maintaining a constant angle and drifting diagonally (like slicing the cheese) to prevent grooving in the blade. Always start with the roughest, then finer, then finest, unless the knife is already sharp. To simply keep it sharp, start with middle roughness or fine, but end on the finest possible.

• Do I need any other tools?

I suggest either a clamp with a long end or a specialized sharpening guide. See below and other answers on this page for examples.

• Do I need any protective equipment?

You shouldn't need anything special for the hand-sharpener you show here. You might use leather gloves to prevent minor accidents, or latex/nitrile gloves if you are using petroleum lubricant.

• Do I have to use some type of oil?

Some stones use water, some oil, some either is optional. Your picture looks like the kind that uses oil, optionally. I suggest you try Flitz metal/plastic polish at least once, but if normal oil/water is used then here is a list of choices that are recommended by specialists and pros beside myself in order of kitchen-safeness and effectiveness:

• Simple Green (professionals use this)
• Mineral oil (cheap at drug store. Graphus suggested mixing with mineral/white spirits, for viscosity)
• Crystalube (branded silicone-base lubricant for abrasives)
• Water with very light detergent (pre-soak stone if it's a true water stone)
• Diesel or kerosene
• Amsoil (purely synthetic) 0W-30 (very thin) motor lubricant.

Do not use any vegetable oils, because they will gradually gum your sharpener.

Always polish and clean the knives (in that order) thoroughly before using them on or around food.

• Is it better to go fast, or slow?

That varies by the person and the materials. If you can safely maintain a constant angle, you should go as fast as you are able, because using these stones is a slow and tedious process. Generally slower is better because most people cannot maintain a constant angle while stroking fast, and that is much more significant to the time it take to sharpen than the strokes per minute. Also, heat produced will weaken the metal and possibly slow the effect per stroke. If using a lubricant and keeping the stone wet, it should be heat-safe to go as fast as humanly possible.

• Is the procedure different with a knife that has never been sharpened before?

The procedure is the same, but there are a few small things to be aware of when sharpening a new knife: Is the blade edge already at the best angle for the type of knife? Is it serrated?

If the edge's bevel is not right for the type of knife (most should be about 20 to 25 degrees bevel from the center-flat plane of the blade), you have to correct it with extra time spent on the roughest stone.

If it is serrated, you should start with no more than medium roughness and have a plan for polishing/deburring the serrated side if necessary. With your kind of stones, it is only possible to sharpen the flat side of a serrated knife. You must be very careful to keep the flat side or the flat side's bevel completely flat against the stone. This can ruin the polished finish on some knives.

• Do I have to do anything different if the blade has rust on it?

If the blade has rust on the edge, just sharpen it with the roughest stone on both sides until the rusted area is completely replaced with a shiny, new edge. If rust is elsewhere, rub out what you can with a 220-grit rubber/abrasive composite brick (resembles a big, black eraser), then use Flitz and a thick scrap of cork or a hard sponge to scrub the remaining rust out until it looks smooth and shiny again.

• How do I know when the knife is sharp?

First, be aware that hand sharpening with a stone of this kind is very slow. It might feel like using a horse and carriage on the freeway. Many people who have the patience for it lessen used the time by taking good care of their knives and touch-up sharpening often.

That said, it is best keep sharpening past the point that you "think" it is sharp, because the sharper the knife, the less resistance it has to cutting something and the longer it may stay sharp. Some common tests are:

• Wipe the edge clean with a microfiber cloth and look straight into the edge with a light being positioned behind you. If you see light shining off the edge of the blade, it is not yet sharp.
• Test it on something normally difficult to cut, like scrap cork or scrap bamboo. If you can cut a thin shaving with a smooth, possibly shiny surface being left by the blade, it is probably as sharp as you will ever need it.
• Just cut something (nothing you intend a human to eat), like banana peel or paper or what ever is near you. If you are not very picky, or dull the knife frequently, this will suffice.

General Sharpening Instructions

I wish show two main paths to go to sharpen nearly any knife or scissors. The first is with belt sharpening. Then I will present a few low or no cost options.

The most important thing in sharpening with any tools is a consistent angle through all grades of roughness. If you have an assembly that insures this, you can skim to the next paragraph, otherwise there are three techniques that will yield adequate results.

• First, a three-foot clamp is long enough to insure accuracy if the opposite end is held in place, either free-hand or anchored.
• Many sharpening services use a simple lean-to metal rod, like a clamped dowel rod, that can guide the flat side of the blade.
• Last, you can create or buy a V-shaped guide that fits around the belt and only lets the blade in a single way. The Work Sharp Ken-Onion Edition sharpener is a good example of this.

The simplest and most flexible to use is the three-foot clamp, or a one-foot clamp for hand sharpening on a bench or table.

After the angle, the next most important thing is to go through multiple grades of roughness. Going straight to fine (from 300 grit to 3000 grit) with eagerness to see a sharp edge will be very slow and wear out the fine abrasive belt more than necessary. The magic in "grit" measurements is to go up approximately 70% of the current grit. For example: 200grit to 360grit, 400grit to 700grit, etc.

The last most important practice is to use the right belts and medium. If your belt grinder comes out of a typical hardware store, then all except 220 grit ceramic belts may have to be mail ordered. The best belts for any size grinding system will be the Eastwind Diamond Abrasives products, but they must be water cooled (a fast dripper or water stream added to grinder frame). Another great wet/dry belt would be cork-composite-grit which range from around 120 grit to 800 grit to no-grit. If you want the blade sharpened super-fine and you use the cork-based belts, then you will need to have a Surgi-Sharp leather belt, as well.

As a general rule, plain aluminum oxide and silicon carbide belts either wear out too quickly or are too slow. If you need to sharpen ceramic knives and you don't have diamond, however, you will need the silicon carbide.

Water cooling/rinsing is the best, but if that is not possible, then frequent use of a belt lubricant is required to keep the belt from loading too much in the abrasive surface and to keep the heat down. If the blade gets too hot, the carbon will burn away, softening the metal, and the heat may shorten the life of the belt drastically. A big green 2000 grit compound block, or a silicone-based Crystalube syringe should be the bare minimum.

Now, there are only two definitely-need-to-know items left. Never put the sharp edge of a blade to a medium-to-high speed belt opposite to it's running direction, except with the thickest, hardest-abrasive belts, and with a tensioning back-plate under the point of contact. If the belt material is soft or if the belt vibrates in the slightest it will probably catch on the edge of the blade and be cut up and destroyed. The last item to need to know is to always keep the belts trued with a dressing stone (a ceramic stick made with 220 aluminum oxide). Without this, the belts will have inconsistent performance and will break down faster.

If you want to invest little or no money into the matter, There are four options:

(1) Go to a thrift store or junk yard and look for several roughnesses of straight, narrow ceramic or hard glass materials, like car windows with dulled edges, kitchen-ware, or large heating element insulators. Most ceramic and hard glass objects make good sharpening surfaces for a medium sharpening.

(2) Any whet stone or nickel plated diamond sharpener that can be used on a bench or flat surface. These are common and available in almost any camping store, just don't expect razor sharp results.

(3) An old real solid leather belt (layered leather doesn't work well). Just a little polishing compound and you can strope a knife like an old-fashioned razor.

(4) A can or tube of Flitz polish, if you have one in your garage. This with the leather or any flat-micro-textured surface makes a beautiful, shiny, sharp finish.

Even with these cheap methods, remember to use a one to three foot clamp to hold the blade at exactly the same angle (ideally 20 degrees on each side, approaching 40 degrees total edge angle), except of course, the stropping with leather belt. This can be done on a bench, but may work poorly. Also, with all methods, you must carefully, thoroughly scrub your finished blade, since there will be metal particles too small to see in all the microscopic grooves that could end up in your food and your body.