The Sharpening FAQs from the Usenet News Group rec.knives
Author: Joe Talmadge
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When I started writing this FAQ, I began by writing a detailed treatise on how to sharpen. I soon found that there was no way I could do this in the kind of detail I wanted without ending up with a book-length FAQ. As it turns out, someone has already written a book on sharpening, and done a better job than I could have done. So the most important part of this FAQ, for the beginner, is the following recommendation: the first thing you need to do is buy and read _The Razor Edge Book of Sharpening_ by John Juranitch. No matter what sharpening system you end up using, the fundamentals as laid out by Juranitch remain intact. I don't agree with Juranitch on everything, but the illustrations he gives really help with understanding the principles.
So this FAQ will discuss the central elements of sharpening, and then go on to more detailed subjects. Sharpening angles, hones, sharpening systems, the latest fads in edges (e.g., chisel grinds), etc. Basically, Juranitch will show you how to get a burr and grind it off to end up with a sharp knife. Hopefully, the FAQ will tell you everything else.
For many people, when they try to sharpen a knife, the knife actually gets duller! If it's any consolation, I was in the same boat at one time. The best way to start out is to read about the sharpening fundamentals, and then use some kind of sharpening system (discussed below) that pre-sets the angles. That way, you can begin by learning how to raise a burr, feel for the burr, and then grind it away, without having to worry about keeping the angle consistent as well. When you understand how to sharpen, then you can get rid of the rig, buy some flat hones, and learn how to sharpen freehand.
II. The Fundamentals of Sharpening
Getting a Sharp Edge
Okay I lied about not discussing the sharpening ritual itself. Here's a much-too-short review of the sharpening process, before we get into the rest of the FAQ. If this section is confusing, read _The Razor Edge Book of Sharpening_. Many of the subjects in this section (e.g., stone grits) are explored further elsewhere in the FAQ.
You grind one edge along the stone edge-first until a burr (aka "wire") is formed on the other side of the edge. You can feel the burr with your thumb, on the side of the edge opposite the stone. The presence of the burr means that the steel is thin enough at the top that it is folding over slightly, because the bevel you've just ground has reached the edge tip. If you stop before the burr is formed, then you have not ground all the way to the edge tip, and your knife will not be as sharp as it should be. The forming of the burr is critically important -- it is the only way to know for sure that you have sharpened far enough on that side. Once the burr is formed on one side, turn the knife over and repeat the process.
To re-cap, you've sharpened one side only until you felt a burr along the entire length of the opposite side, then you switched sides and repeated the process. I suggest you do not follow the directions that come with many sharpeners, of the form "Do 20 strokes on one side, then 20 strokes on the other". You go one side only until the burr is formed; if that takes 10 strokes or 50 strokes, you keep going until you get a burr, period. Only then do you flip the knife over and do the other side.
Having raised a burr, our job now is to progress to finer stones, in order to make the edge smoother and remove the burr. So now we run the blade along the stone from end to tip, this time alternating sides with each stroke. Switch to a finer stone, and then do it again.
Sometimes, the burr is turned directly downwards during sharpening, and since it is very thin and razor sharp, it seems like an incredible edge. This is called a "wire edge". But being fragile, it will break off the very first time you use the knife, leaving you with an extremely dull knife. If you seem to be getting good sharpening results on your knives, but they are getting dull very quickly with little use, you may be ending up with a wire edge. If that's the case, you'll need to be careful and watch out specifically for a wire edge; you should try progressing down to finer stones, try double-grinding the edge, and give the knife a quick stropping once you're finished (all these terms are explained below). If your knife is fading fast as you're sure it's not because you left a wire edge, steeling between uses may be what you need. My last few strokes on the stone become progressively lighter, to avoid collapsing the edge and raising another burr.
On a badly-worn or damaged edge, I'll typically start with a medium (300-400 grit) stone, then move to a fine (600 grit) stone, and then sometimes I'll finish on an extra-fine (1200 grit) stone if I want a more polished edge. However, once my knife is sharp I try to re-sharpen before it gets too worn down. In that case, I can usually start on the fine stone. But be sure to read the important notes on grits later in the FAQ.
Lastly, I may use a leather strop on the knife.
On other sharpening systems, the same fundamentals as laid out above still apply. For example, on a V-type sharpener, I'll start by sharpening one side only against the right-hand stick until a burr forms. Then I switch to the other stick until a burr forms. Only after I've raised a burr from both sides will I follow the manufacturer's directions and alternate from one stick to the other between strokes.
The smaller the angle, the sharper your knife will feel. But the smaller the angle, the less metal that's behind the edge, and thus the weaker the edge. So your sharpening angle will depend on your usage. A surgeon's blade will have a very thin, very low-angle edge. Your axe will have a strong, thick, high-angle edge.
Something like a razor blade will having an angle of around 12- degrees, and it's chisel-ground so that's 12-degrees total. Utility knives will have angles anywhere between 15- and 24- degrees (30-48 degrees total). An axe will have something around a 30-degree angle.
For double-ground utility knives, a primary edge of 15-18-degrees, followed by a secondary grind of 21ish-degrees, works well. Don't be obsessed with getting the exact right angle; rather, make sure that at whatever angle you've chosen, concentrate on holding it precisely.
See also the sections on convex edges and chisel-ground edges.
What Kind of Stone?
Basically, a stone needs to cut metal off the edge. The stones below do this well, and for most of us our time would be better spent actually learning how to sharpen than worrying too much about the minor advantages of one stone vs. another. Get the biggest stones you can afford and have room for. Big stones make the job much much easier.
The time-honored stone is the arkansas stone. Soft arkansas stones provide the coarser grits, with harder stones providing finer grits. Many people use oil on these stones, ostensibly to float the steel particles and keep them from clogging the stone. John Juranitch has popularized the notion that oil should absolutely not be used when sharpening, and indeed results from people using arkansas stones without oil have been very positive. However, if you have ever used oil on your arkansas stone, you need to continue using it, or it will clog. If you never put oil on your arkansas stone, you will never need to.
Synthetic stones are very hard, and won't wear like natural stones (a natural stone may get a valley scooped out of it over time). They clean well with detergent-charged steel wool, I use SOS detergent pads, they clean very very fast and very well. I know you're thinking that cleaning with steel wool will cause the stone to shear off the steel wool and fill up the stone even worse! But I assure you that is not the case, for whatever reason SOS pads clean synthetic stones, they do not make the stones dirtier. Spyderco and Lansky are some manufacturers who sell synthetic stones.
Stones with diamond dust embedded in them cut aggressively. You can remove metal very quickly if you need to, but be careful lest you remove too much too fast! DMT, Eze-Lap, and Lansky are some manufacturers who sell diamond-based hones. Some diamond stones have the problem that the diamond dust wears off quickly, leaving you with a useless stone. I have experience with the DMT stones, and can say that they do not have this problem.
Natural stones will eventually dish out in the center with use. To flatten them back out, put some sandpaper on a flat surface and rub the stone top on it. Wet/dry 400 grit sandpaper mounted on a table top or glass is reputed to work well.
Should I Use Water or Oil on My Stone
John Juranitch has popularized the notion that no liquid should be used on the sharpening stone. Since oil has been used for many years on stones, this leads to some confusion.
Basically, the purpose of the stone is to rub against the blade and remove metal. Slippery liquids, like water and especially oil, make the rubbing slicker, causing less metal to be removed, causing sharpening to take longer. On top of that, Juranitch claims that as your edge is being sharpened on the stone, the oil-suspended metal particles are washing over the edge and dulling it again.
On an arkansas stone, the oil is supposedly needed to float metal particles away from the stone surface, lest the stone clog and stop cutting. Some people on this group have used their arkansas stones without oil or water, and have reported good results. However, if you've already used oil on your arkansas stone, you'll probably need to keep using oil forever on it, because an already-oiled stone will clog up if not kept oiled. If you have a fresh arkansas stone, go ahead and use it without the oil, and things should be okay.
I've used diamond and synthetic stones without liquid, and they worked just fine.
In any case, the bottom line is: use liquid or don't. Using the liquid will make the sharpening process slower and messier, but if you insist on using liquid and are willing to spend more time, that's your call. If you don't have the skill to hold a consistent angle, it's all moot anyway!
How Fine Should My Stone Be? Important notes on grits!
The finer the stone, the more polished your edge will become. The rougher the stone, the more the scratches in the edge function as "micro-serrations". Though the actual ontological status of the micro-serrations is debatable (Juranitch says there's no such thing, having looked under a microscope), the serrated effect of the coarser grind is undoubtably there.
The more polished the edge, the better your edge will work for doing push-cut applications like shaving, whittling, peeling an apple, skinning a deer. Also, your cut will be more clean and precise with the polished edge.
A rougher, more micro-serrated edge will work better for slicing-type applications like cutting through coarse rope, wood, etc. The serrations present more edge surface area, and tend to "bite" into the thing being cut.
It is possible to get an edge that will shave hair with a medium (300-400 grit) stone, with practice [I specifically mention stone grits because many manufacturers call the 300-400 grit stones "coarse" rather than "medium"]. The medium stone will have pretty big micro-serrations. In previous version of the FAQ I stated that I find this too rough a finish for my general utility edge. However, I've since found this to be a really nice edge finish for utility work -- it won't shave great, but it does a really nice job on cutting coarse materials.
Anyone should be able to get an edge that shaves hair easily with a fine (600 grit) stone. I find this to be a pretty useful finishing stone, leaving enough micro-serrations for general utility work but still being hair-shaving sharp.
An extra fine stone (1200 grit) should start polishing the edge, and you should end up with a hair-popping sharp edge. This is also a good choice for a general utility finish, especially on a partially-serrated blade, where the serrations can be used when the slightly-polished main part of the blade becomes less effective.
************ IMPORTANT TIP ****************
Many treatises on sharpening tend to focus on getting a polished, razor-like edge. This is partially the fault of the tests we use to see how good our sharpening skills are. Shaving hair off your arm, or cutting a thin slice out of a hanging piece of newpaper, both favor a razor polished edge. An edge ground with a coarser grit won't feel as sharp, but will outperform the razor polished edge on slicing type cuts, sometimes significantly. If most of your work involves slicing cuts (cutting rope, etc.) you should strongly consider backing off to the coarser stones, or even a file. This may be one of the most important decisions you make -- probably more important than finding the perfect sharpening system!
Recently, Mike Swaim (a contributor to rec.knives) has been running and documenting a number of knife tests. Mike's tests indicate that for certain uses, a coarse-ground blade will significantly outperform a razor polished blade. In fact, a razor polished blade which does extremely poor in Mike's tests will sometimes perform with the very best knives when re-sharpened using a coarser grind. Mike's coarse grind was done on a file, so it is very coarse, but he's since begun favoring very coarse stones over files.
The tests seem to indicate that you should think carefully about your grit strategy. If you know you have one particular usage that you do often, it's worth a few minutes of your time to test out whether or not a dull-feeling 300-grit sharpened knife will outperform your razor-edged 1200-grit sharpened knife. The 300-grit knife may not shave hair well, but if you need it to cut rope, it may be just the ticket!
If you ever hear the suggestion that your knife may be "too sharp", moving to a coarser grit is what is being suggested. A "too sharp" -- or more accurately, "too finely polished" -- edge may shave hair well, but not do your particular job well. Even with a coarse grit, your knife needs to be sharp, in the sense that the edge bevels need to meet consistently.
Stropping consists of running the edge along a piece of leather charged with some kind of abrasive like stropping paste or green chromium oxide (I had previously said jeweler's rouge is okay, but have since heard that a more aggressive cutter is needed). It is done for a short time to finish off the burr, or for a long time to give the edge a final polish. Stropping is an easy-to-use finishing step (as opposed to the difficulty in keeping a consistent angle on a stone).
Before you strop, remember to wash and dry your newly-sharpened knife. If you don't, you might grind leftover metal particles into the strop itself. If you need to charge your strop, put a little paste on your fingers and rub it into the leather.
To strop, you run the edge along the leather with the blade positioned spine first and the edge trailing (opposite way from sharpening on a stone). With a thin straight razor, the spine of the razor is always kept on the strop, and direction is switched by flipping the razor over along its spine. In my experience, this isn't necessary with a utility knife. You can strop with the blade spine raised above the leather (don't lift too high -- if the edge bites into the leather, that's too high), and change directions by lifting the entire knife up, turning it over, and placing it back down.
If you've never stropped your knife before, give it a try. It will come out very sharp, but of course polished and so optimized for push-type shaving cuts. The strop to some extent can make up for less-than-perfect sharpening technique -- a sharp knife can be made extra sharp on the easy-to-use strop. However, I always tell people that they should be able to get their knife scary sharp without the strop; don't let the strop keep you from recognizing weaknesses and improving your technique on the hone!
In the absence of a strop (say, out in the field), many people use their jeans and then their palm as a strop. There's probably no need to point out the danger in this practice, so don't do it. That said, I must admit to having done this myself on numerous occasions, and having gotten good results.
A safer and more effective trick is to use cardboard (say, the cardboard back of a standard notepad). You can optionally charge the cardboard with metal polish, just rub it in with your fingers. Then strop as above. Even without the polish, the cardboard will strop acceptably. Stropping with cardboard has become a de-facto standard last step for sharpening chisel-ground (single-side ground) knives these days, for burr removal purposes.
Using a Steel
Please see our instruction page for steels HERE
The sharpening steel should be an important part of your knife maintenance strategy, and is maybe the most mis-understood part.
When you use a knife for a while, especially a knife with a soft, thin edge like that found on a kitchen knife, the edge tends to turn a bit and come out of alignment. Note that the edge is still reasonably sharp, but it won't feel or act very sharp because the edge may not point straight down anymore! At this point, many people sharpen their knives, but sharpening is not necessary and of course decreases the life of the knife as you sharpen the knife away. It's also akin to putting in a thumbtack with a sledgehammer.
The steel is used to re-align the edge on the knife. Read that last sentence again. Re-aligning the edge is all the steel needs to do. It does not need to remove any metal. Since the steel's only function is to re-align, the sharpening steel can be perfectly smooth and still do its job. You'll see many bumpy steels on the market, but this is almost certainly because consumers think that steels must have bumps to work. The bumps can actually mess up the edge, and make the work of steeling more difficult.
There are two schools of thought on steels. Some people use grooved steels, which align the edge more aggressively but are harder on the edge. I use a smooth steel, which is easy on the edge but may align the edge more slowly.
To use the steel, run the knife along the steel on one side using light pressure -- no more pressure than the actual weight of the knife is required! Then switch to the other side and do it again. Repeat a number of times until your edge feels sharp and nice again. I hold the steel in my left hand, the blade in my right, and lightly run the blade along the steel while keeping the steel stationary, but it's perfectly fine to move both steel and knife past each other at the same time, or whatever works for you.
Most people run the knife down the steel edge first, the same direction you use when sharpening. This yields good results. However, theoretically going edge-first along the steel could bite into the edge while straigtening it, and so many people like to go spine-first (like when stropping) instead. This method also works well, and I personally have begun to feel that steeling in this direction gets my edge the tiniest bit sharper. It is more awkward to go spine-first, so if you have any trouble with it switch to edge-first, and your edge will end up just fine.
If you steel your knife every time you use it, you will significantly lengthen the time between sharpenings. I've found steeling to be critical on kitchen knives, but it's an incredible help even on ultra-hard ATS-34.
III. Putting it all together
Some tips and tricks
If you want to determine if you are sharpening at the same angle that the blade already has, try this easy trick. Mark the edge bevel with a magic marker. Then go ahead and do a stroke or two on the stone (or take a stroke with your Lansky, or whatever). Now pick the knife up and look at the edge. If you have matched the edge angle exactly, the magic marker will be scraped off along the entire edge bevel. If your angle is too high, only the marker near the very very tip will be gone. If your angle is too low, only the marker near where the edge bevel meets the primary bevel will be gone.
Another trick is to use light and shadow to get the edge precisely. Using strong directly light, lay the edge down on the stone and watch the shadow below. As you tilt the spine up, the edge contacts more of the stone and the shadow disappears. As the shadow just disappears and the edge just touches the stone, that's your angle. If you go higher than that, you should be able to see the edge tilting over onto the stone.
One trick to freehand sharpening is to use your thumb as a guide. I'll place the spine of the blade against my thumb pad, and rest my thumb on the stone. That way, I can feel the angle between the knife and stone, and make sure that it is consistent. Typically, the hardest part to freehand sharpen is the curving belly of the blade, as keeping a consistent angle here is more difficult.
I use all these tricks extensively when sharpening freehand, and use the marker trick even when I'm using a sharpening rig.
One thing to keep in mind is that there's no reason you need to keep the factory edge. If you're happy with that edge, great. However, many factory edges are too thick to really cut well. If you're unhappy with the cutting ability of your knife, don't be afraid to try lowering the angle a bit.
Why does my knife go dull so fast?
A frequent complaint I hear is, "I sharpened my knife and did a good job, it was really sharp. But then after just a few uses it went dull." Why does this happen?
One of the following factors -- and many times a combination of those factors -- is at play:
- Wire edge If the burr is not properly ground off, but is instead turned downwards, your knife will feel razor sharp. However, the burr quickly turns or snaps off, leaving you with a very dull-feeling knife. Be sure to use a light touch at the end of the sharpening process and make sure the burr is gone.
- Thin, weak edge
If the bevel angle you chose for your knife is too thin for your usage, the edge can chip and get really wavy. Try using a larger edge angle, or at least double-grinding the edge.
- Edge turning
In regular use, all edges turn to some extent. If your edge is much too thin, it will be damaged as above in #2. If it's only slightly too thin, it will quickly turn out. As long as the the edge is not being damaged, but simply turning, you don't necessarily need to re-grind a thicker edge. Instead, see if frequent steeling will give you the performance you need, it can really work wonders. Keep in mind it's difficult to see a turned-out edge by eyeball -- only using the steel will tell you conclusively if this is your problem.
- Thick edge
A thin edge will feel sharper than a thick edge. If your edge is too thick, when it starts to dull even the slightest bit it may no longer feel so sharp anymore. Consider using a lower angle and seeing if that helps. Of course, your thinner edge will be more fragile than the thicker edge, so you may end up chipping the edge out, and the thinner edge may not be feasible. I personally feel that this is rarely the real problem, so be sure to try the other solutions first.
- Soft steel
Occasionally, a manufacturer or maker will make a mistake while heat treating, and the steel in the blade will end up too soft. No matter how well you sharpen, your blade will still go dull quickly. Often, soft steel is the first thing people point at when their edges dull quicker than expected. But this problem really is relatively rare; in the vast majority of cases, it is one of the above reasons rather than soft steel that's the problem. So if your edge dulls too fast, don't blame the steel until you've exhausted the above options. If it's still dulling quickly, contact the manufacturer, they are often interested in testing to see if they made a mistake.
Keeping bevels even
With the burr method of sharpening, one side of the knife can end up with more metal taken off it than the other side. This forces the edge to be not-quite-centered. This normally doesn't affect performance, but aesthetically it doesn't look quite right. This happens because as you grind the one side to create the bevel, it has to go far (that is, lots of metal has to be removed) to create the bevel on the other side. When you flip to the other side, the edge is already thin, so very little metal has to be removed to flop the burr back over. There are a few ways to avoid this.
First, you can just switch which side you start sharpening on. If you start with the edge that's on the right side of the blade, that edge bevel will be a little bigger than the one on the left side. So next time you sharpen, start off on the left side. You can pick which side to start your sharpening on by just using whatever side seems to have a smaller edge.
The method I use is to switch sides while trying to get the initial burr. If I start on the right side, I'll sharpen for 20 seconds or so and then check for a burr. If no burr is found, I switch to the left side and repeat. I keep doing this -- sharpening one side for a time, then the other side -- until I finally start to feel a burr. Then I just follow the normal directions: I keep sharpening that side until the burr goes the entire length of the edge, then flip and get a burr along the entire length of *that* edge. The fact that I'm flipping the knife keeps the edge bevels even.
Putting it all together
As you use your knives, you may see your sharpening strategies change. Many of us seem to be homing in on the philosophy that you should choose the thinnest, coarsest edge possible that can do your job without the edge being damaged, especially in the context of general usage.
Thin blades and low-angle edges seem to cut better than thick ones. They slide through the material being cut with less effort. Which makes sense -- the wider the V that your edge forms, the more metal you're pushing into the material. However, go too thin and your edge can chip out. So go as thin as you can without damaging your edge, and use a steel often to touch it up. Obviously, what "thin" means depends on usage. "Thin" means one thing when the job is slicing soft materials, something else entirely when chopping hard materials. Lightly double-grinding a shallower bevel on a thin edge may help give you the best of both worlds. If your first bevel is a thin 15-degrees (say), try doing a few light finishing strokes at a stouter 24-degress.
Coarser edges slice better than polished ones, but a polished edge will laterally push-cut (e.g., shave) better. If you find yourself doing a lot of lateral push cuts, then you'll obviously want to polish your edge more. However, most people do much more slicing than push cutting, and as a result end up with a much more polished edge than optimal. You should play around with coarser grits. The edge won't do as well shaving hair, but unless this particular knife is a razor blade, who cares? You may find the knife cutting through other materials much better than usual.
Lastly, I have become something of a steel fanatic. Steeling your knife frequently -- even if the blade is of really high-hardness steel -- works wonders on the edge. It also allows you to have a slightly thinner (and hence better-cutting) edge, because if you steel frequently you'll keep the edge aligned. If you don't steel at all, you'll have to use an edge that's thick enough not to turn, and that may negatively affect sharpness and cutting power. Remember to steel frequently, because if your edge's shape gets too bad, the steel won't work and you'll have to go back and sharpen.
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