2-20-2018

Sharpening Knives

The following post is from Blade Forums and is an excellent (and often referred to) description of what knife sharpening is all about: Here is my copy in case the above vanishes (as so often happens):

As you read this, bear in mind the following "grit equivalents" for the Spyderco sharpmaker rods:

Also note that these are rough equivalents. The sharpmaker rods are ceramic, and they have a surface texture that determines how they perform, they are not composed of graded grit like many stones.

I also own a DMT bench stone that is 600 on one side and 1200 on the other.

Here is the essay by "Magnanimous_G":

What is sharpening a knife really about?

What is sharpening a knife really about? Simply put, it's about forming a clean, new edge (i.e., apexing the edge and removing the burr). When I first tried my hand at freehand sharpening, I would work on the stones forever, going all the way up to the Spyderco Ultrafine bench stone until the bevel would be polished like a mirror. Id look at it in the light and be very proud. Wow, did it glimmer! Then I'd try to cut a piece of heavy stock copy paper (the easiest paper to cut, by the way)... and the edge wouldn't cut it. My mirror-polished bevel was duller than my Ikea butter knives. And I got so frustrated, Id want to cry. It took a while for me to understand what was going on between the stone and the edge. Fundamentally, I didn't understand that there were things I should have been watching for, carefully like a hawk. I thought it was a math game: "5 strokes this direction, 5 strokes this direction... whew, Ive been at this for a while, so I guess its time to move to the next stone." To the contrary, moving on to the next stone is about knowing *when* to do it. (explained below)

Refinement vs. Sharpness

Sharpness does not equal refinement. They are not the same thing, at all. Related, but different. You can get a push-cutting edge on a DMT coarse stone if the edge is apexed and the burr removed. The bevel will look like you took an old rusty file from grandpas shop and attacked your knife but it will push cut paper. Why? Again, because sharpness is not about refinement. Its about apexing the edge and removing the burr. So what is refinement? Refinement is about making that apexed edge smoother and less toothy. So why do we refine an edge? Why not just finish on one coarse stone? The reason why is because the coarse stone leaves an extremely toothy and jagged edge which will deform easily and dull quickly. People refine edges to get a cleaner, smoother, longer-lasting cutting edge. The extreme example would be a straight razor polished by a honemeister. You see, even though you can get a scary sharp edge off of a 1k stone, it wont shave smoothly (i.e., it will irritate your face). You need to go much higher in refinement, to 16k, or 30k, or JNats, or Belgium Coticules to smooth that edge out to the point its like glass and doesnt irritate the skin. Thats refinement. Not sharpness.

2015 UPDATE: Revisiting this thread after three years, I should clarify that yes, refining an edge makes it sharper. David Martin has a point. That said, its still important for a new sharpener to divorce the two ideas in his head. Too many new sharpeners dont achieve a sharp edge coming off of their coarse stone, and they conclude that its because they need to go finer to get a sharp edge. That is often not the case. Far more often, the problem is that they didnt fully apex the edge and remove the burr. But yes, all things being equal -- and doing all things right with the stones -- going finer will indeed give you a sharper edge because the apex will be capable of finer cuts.

So what degree of sharpness and refinement should I be going for?

So what degree of sharpness and refinement do you need? You *always* need the ultimate in sharpness: a fully apexed edge that is burr free. What degree of refinement do you need? It depends on how you use your knife. For most kitchen knives and pocket knives, the degree of refinement that is ideal is probably between the two extreme examples above (DMT Coarse and 30K water stone) maybe 1 - 2K (previously 2 - 10K). You can achieve this with two stones: something Medium and Fine (those are not exact terms and will vary among sharpening mediums and brands). Most people who are hobbyist sharpeners (like me) have added coarser stones (for quick reprofiling and edge correction) and finer stones (for greater refinement). Professional sharpeners may have many more. Then again, many professional sharpeners only use two cheap stones. I know that Murray Carter only uses a 1k and 6k King stone, for example, and he has been sharpening professionally for twenty years (although he has a large powered stone wheel for bevel setting and reprofiling work).

2015 UPDATE: I was probably too generous with refinement needs in my first shot at this post. 10k is very refined, to be honest. For normal kitchen duty with the typical knife that most people have in their kitchens (mid-range Wusthofs and Henckels), 4k is more than enough, in my experience. Frankly 2K is probably plenty. And I was probably too generous for a working knife, too. 2k is good, but again, its probably more work than its worth. 600 - 1k is probably fine for a sodbuster thats going to see work.

Newbie sharpening mistakes explained

Okay, so in real terms, I think these are the most common mistakes of new sharpeners:
  1. didn't spend enough time with the coarse stone establishing the bevel and correcting problems (i.e., grinding past chips, obtuse factory grinds, etc.)
  2. didn't check the edge often enough (to be sure that that scratch pattern is established all the way to the apex)
  3. didn't know *what* to check for
  4. didn't understand that the final stone is for cleaning that edge up to the maximum (the mirror bevel is just a side-effect, not the goal).

I would wager that, under magnification, most new sharpeners edges done freehand have lots of uneven lines from inconsistent angles on the stones (which takes practice to be able to achieve a consistent angle with each stroke). Also, the edge bevel probably isnt even (especially at the tip and/or heel of the edge), and the scratch pattern isnt fully established (and the edge isnt apexed fully). And I would wager that this is because they were making it a math game and werent really sure when to move to the next stone. Its not about a certain number of strokes on one side or the other. Its about when the scratch pattern is fully established (transferred from the stone onto the bevel, like an imprint), all the way to the edge, until spending more time on that stone would be a waste of time as one wouldnt be changing anything but rather only removing more metal needlessly. So the thing to know is *when* that has happened and thus *when* to move to the next stone. And that's the topic of the next section:

2015 UPDATE: See this thread on sharpening technique, also here are links to some of the You-tube videos mentioned in that thread.

How do you know how long to sharpen and when to move to the next stone?

The way to know how long to sharpen and when to move to the next stone is by concentrating on keeping a consistent angle with your first (coarsest) stone and not being afraid to work that stone. You won't hurt your knife. Work that bevel until it's one even, clean scratch pattern from tip to heel. This can be *very* difficult to see if you are new to sharpening, so I highly recommend investing in a 22X loupe (previously 10X or 15X). (2015 UPDATE: a 22X loupe will let you see everything much clearer). I prefer Peak brand. There are others. This will let you really see what your edge looks like. But even with the naked eye, if you look really close, you should see if you are making an even bevel from tip to heel with no areas of that bevel that don't look like the rest of the bevel (this is usually the case near the heel and near the tip for new sharpeners and for factory knives that have never been sharpened).

It will probably be slow-going for the first few sharpening sessions, too, because it takes time to get comfortable holding the knife correctly and establishing the motions, which are not natural to most people. And regardless of your sharpening skill level, you will always have to spend time with that first stone. In fact, in my humble opinion, 80 - 90% of the work of sharpening is on that first stone because you are correcting problems and establishing an even scratch pattern. The higher grit stones are only used to remove that coarse scratch pattern on your now perfect bevels and then to replace it with the higher grit scratch pattern. Then you move on to the next stone and repeat until you are finished with the highest grit stone.

2015 UPDATE: Besides a loupe, just looking straight onto the edge under bright light (held perpendicular so the edge is facing up) will allow you to see dull spots and damaged areas, and places where the edge is not fully apexed. Here I will give credit to FortyTwoBlades for pointing that out later in this very thread: Dull spots may often be identified by examining the knife edge up under bright light and looking for spots that reflect light. This indicates either a dulled, rolled, or chipped spot on the edge, as it has been widened enough for you to be able to see the light reflecting off of the spot.

Burrs!

Burrs: to establish or not to? Heres the dirty secret: you will always establish a burr if you are sharpening correctly. Even if you are using a Sharpmaker and dutifully stroking once on each side, from one side to the other and back again, you will work up a burr as each stroke works that bevel and creeps to the edge. Its just so small and thin you cant see it or feel it. When people say, You need to work up a burr, they mean really work up a BIG burr that you can easily feel with your finger. You do that by working one side a lot. Then that big burr gets raised. And the reason why they tell you to do that is because this is a good way to know that you have indeed apexed that side. But how much of a burr you work up isnt important. You just need to have worked that side until youve scratched the whole bevel to the edge. The burr is just a side effect of doing that, and yes, it is a good reference for a new sharpener. Okay so let's say you've done that. And then you do the other side, carefully keeping an even angle and working the whole bevel from heel to tip and completely replacing it with that particular stones unique scratch pattern. Okay. What happens then? Lets talk about results

2015 UPDATE: For new sharpeners, I strongly recommend the bring up a big burr method. I mean, keep working one side until you can unmistakably feel that burr on one side, all along the edge, from heel to tip. There will be great temptation to feel for the burr and then switch to the other side, even though you havent really brought up the burr along the whole edge. Really work up a burr that is blatantly obvious to the touch, ALL ALONG the edge, from heel to tip. This is important because new sharpeners, sharpening an old pocket knife or kitchen knife, can easily overlook or neglect those spots that usually need a little more work, such as the main cutting edge between the tip and the halfway mark of the knife, for example. You may find yourself going all the way up your grit progression before realizing you didnt really hit the apex in that spot (stopping to check your edge periodically, and observing with a loupe or under strong light, as mentioned above, can help avoid this).

So how do you feel for the burr? Feel the burr with either your finger(s) or thumbnail, but do it consistently so you get the feel for it. Personally, I run my four fingers forward (in a pushing motion) along the edge, from spine to edge, and I let the ridges of my fingerprints feel for the burr. I can detect a pretty darn small burr that way. Knifenut (aka Jason_B) uses his thumbnail (thumbnails are also very sensitive). Choose whichever, but do it consistently and you will eventually develop a feel for it until you are able to detect even tiny burrs.

Finalizing the edge and getting results

Then you try to cut a piece of paper, and whoa! It cuts! But its rough it catches in places. It tears the paper in places. Why? Because theres still bits of burr on that edge. So you have to get rid of them. There are several ways to do this. Some highly-respected sharpeners (Murray Carter, for example), drag the edge ever so carefully and lightly, with a feather-light touch, through a piece of soft wood, cork, or hard felt. That will do it. I think a much more advanced and elegant way is the knifenut way: a progression of careful edge-trailing strokes, first with firm pressure and gradually lightening until you are just kissing the stone. The abrasiveness of the stone will pull off those remaining bits of burr as you drag the edge backwards across the stone.

Then you try to cut a piece of paper again, and WHOA! It slices cleanly. It doesnt catch in any places any more. Now youve got an apexed, burr-free edge.

If you are not getting those results, do not despair. Practice makes perfect.

How high can/should you go in grit?

So when should you stop? How high of a grit do you need? What compounds should you use to strop? Or should you just strop on newspaper, jeans, bare leather, etc.? That depends on what you plan to do with your knife. Need to put an edge on a kitchen knife? 2k (previously 6k) is all you need. Thats refined enough to last and toothy enough to cut tomatoes effortlessly. Need to shave? 12K or higher, and preferably even higher (30K, or very fine Jnats or Coticules). A straight razor's edge needs to be smooth enough not to irritate skin. Need an edge for a sodbuster or any hard use pocket knife? I dont know, but I suspect 1K or 2k 600 or 1k, done well, will be all you need. So what about the sub-micron sprays on balsa wood and the resulting edges that make feather sticks out of hair? Sure, go that route if you need to make feather sticks out of hair. Again, how refined the edge needs to be is dependent on how you plan to use the knife, but you should always, *always* have a fully apexed, burr-free edge that is truly sharp. That is what sharpening is about.

2015 UPDATE: As mentioned above, I was probably too generous with the refinement needs in my first shot at this. 2K is probably plenty. And I was too generous for a working knife, too. 2k is good, but again, probably more work than worth it. 600 - 1k is probably fine for a sodbuster thats going to see work cutting rope and the like.

And anyone can do it. It just takes practice.

Feedback? Questions? Drop me a line!

Tom's Knife Info / tom@mmto.org