Make it Sharp

Sharpening 101.1 – An Introduction

 

Good morning, everyone.

I’ve been spending a lot of time out in my shop, making small pieces of wood out of larger ones, and spending a significant amount of time doing one of my least favorite chores: sharpening tools. It’s a vital part of any task that involves using edged tools, whether you are doing woodworking or cooking, but it’s rarely any fun and it’s something that you want to be done with as soon as possible. So as I was mindlessly grinding away, my hands painfully cramped around the parting tool I was honing on a diamond stone, and my back screaming in pain, I thought, “Good lord but I’m having a magnificent time! I surely wish that I could share the glamour and excitement of this experience with those keyboard pounders on the AT site.”

So today I’m starting an occasional series of articles on sharpening. Sharpening is one of those subjects that is both simple and complex at the same time. It’s simple because all that you’re basically doing is creating the intersection of two planes on the edge of a piece of steel. It’s complicated because there are a bazillion different ways of doing it, and a myriad of materials and appliances to use in the process. I’ve been trying to figure out a way to write an article for the casual reader that makes sense out of this mass of material and gadgets, and I keep coming up empty. So bugger that. I’ve been sharpening things for over four decades now, so I’m going to go with what I know.

So what is sharpening? Sharpening, in general, is removing the material from the edge of a hard substance, such as steel (or another metal), ceramic, glass, plastic, etc., thinning the edge down to where it is sharp enough to cut other materials. For our purposes, the material being sharpened is usually in the form of a blade of some sort, and the material is removed at one or more angles to the blade so as to produce the intersection of two planes, a plane and a curve, or two curves. The cross section of a sharpened blade is officially called the grind of the blade. I call it a profile, but whatever.

Some common edge grinds

The picture above shows some common grinds found on edged tools:

  1. Hollow grind – you typically get this type of grind when you sharpen a blade on a motorized grinder, which produces concave bevels. It can produce a very sharp edge, but the edge is weak due to its thinness. Straight razors have this type of grind, and some special cutting tools the names of which I can’t remember right now.
  2. Flat grind – the blade is ground in a taper from the spine to the edge so that each side of the blade is a bevel. You can get an extremely sharp edge with a grind like this, but they can be a hassle to maintain.
  3. Saber grind – this is a common grind for knives, especially tactical knives. It’s like a straight grind except that the bevel starts much closer to the edge. It can yield a sharp edge that is easier to maintain, and is very strong and durable.
  4. Chisel grind – this is the grind you have on a typical wood chisel, plane blades, and many carving tools. It is also commonly used on Japanese culinary knives, with variations. It can produce a very sharp, strong edge.
  5. Double or compound bevel grind – another common grind, found on most kitchen knives. The primary bevel starts higher up on the blade, then closer to the edge, a secondary bevel is ground forming the cutting edge. The compound bevel makes the blade thinner without sacrificing much strength or stiffness, and makes cutting through soft or wet materials easier.
  6. Convex grind – this grind consists of two convex bevels, and makes a very strong edge that can be fairly sharp. This is the type of grind that you use on axes and some swords. Some knife collectors like this edge because it’s pretty, but it is hard to do properly on flat bench stones.

There are combinations and variations on all of these grinds. The sharpness of the edge depends upon angle of the bevel(s). The edge angle is the angle of the bevel on one side of the blade, and the included angle is the bevel of both sides together. On a chisel grind, the edge angle and the included angle are the same.

When you get to the actual act of sharpening, it breaks down into three general stages. The sharpening stage, where you form the basic grind of the edge with coarse abrasives, the honing stage, where you refine the edge with finer abrasives, and the polishing stage where you use very fine abrasives to further refine and smooth the edge. For certain types of tools, such as most axes for instance, you can usually skip the polishing stage because the work the tool is intended for doesn’t require a refined edge (in most cases). Tools like carving gouges, on the other hand, need to be honed and well polished in order to cut cleanly. Once a blade has been properly sharpened, it just needs to be honed from time to time to maintain its sharpness. When people talk of sharpening, they’re usually referring to this honing process.

And that’s enough for this time. Next, we will talk about the abrasives that I use for various kinds of sharpening tasks.

 

References:

https://en.wikipedia.org/wiki/Grind

 

  • PrawoJazdy

    Now that I know you do this, I'll need your address to send you my knives for sharpening…. err… Christmas cards.

    I have a set of Wusthoff kitchen knives. They're expensive. Be careful.

    • The Professor

      Ah yes, sending knives as Xmas cards. It must be a tradition that I'm unfamiliar with, ho ho ho. If you lived nearby, I actually would sharpen them for you, but shipping is expensive and a hassle.
      Wusthoff knives are very good, so you should take care of them. In later articles, I'll attempt to teach you how to do basic sharpening using a diamond bench stone. It's not difficult to do with a little practice.
      Also, if you have one of those little electric knife sharpeners like they sell at Macys (and similar establishments)? Throw it away, it will ruin your knives. I've never seen one that was worth a damn.

      • PrawoJazdy

        I didn't realize the first time I typed this it was not in reply to you and isntead made a new comment. My bad. I want you to see this question, so I'm writing it again. I've deleted my comment from below.

        Do you recommend the diamond stone over the oil stone I use now?

        One of the first things they taught us in Culinary was never use an electric sharpener. Chef then put some microscopic views of knife edges on the screen and showed us an oil stone sharpening vs. the electric sharpener. You know those pictures of caverns with a ton of stalagmites and stalactites in Nat Geo? Guess which one looked like the cave. You couldn't be more right, they destroy a knife.

        I love my knives more than anything else in my kitchen. I caught a former room mate using one to cut cardboard once. Once.

        • The Professor

          I replied to your original comment, in case you didn't get an email.

  • The Professor

    If you already have a system for sharpening that you're happy with, such as your oil stones, by all means use them. For people that are just learning or don't have a decent bench stone, I usually recommend a diamond stone because they're not nearly so messy, and you can usually get by with just one stone rather than two or three. I use diamonds stones, usually a 600x, when I'm in the middle of doing something and I have to hand hone an edge. It gives a nice fine edge, like a white Arkansas stone, fairly quickly, and doesn't require any lubricants.

  • P161911

    I have one of the Lansky kits I use sometimes on pocket knives and folders. For my nice kitchen knives, JA Henckels Classic, I use a little gadget I picked up years ago. It has a sharpen and a hone section. Each one has two pieces of steel something like this
    <img src="http://gearpatrol.com/blog/wp-content/uploads/2008/03/vulkanus-steel-countertop-knife-sharpener.jpg"width=500&gt;
    but in a small plastic type thing. It seems to do OK, but I know I don't have the skill to sharpen them right with a stone.

    • The Professor

      That's a wild looking thing, I've never seen one of those before. It's the number of devices like the one you show that have made writing about sharpening so difficult for me. There is all of this stuff that I've never used and I have no idea how well it works, how do I discuss it when someones asks? Well, the only answer is, I can't. So in the case of these unknown (to me) gadgets, my basic answer is, if you're satisfied with how well it sharpens your knives, then you should use it. If you're not, or you want to learn how to put a better edge on your edged tools, I am going to try to teach you. With the right materials and some effort and practice, you can put an incredible edge on your knives and tools. It's really not that hard.

    • The Professor

      I just Googled your Lansky kit, and it's another one of those gadgets that I haven't tried. My only concern from reading about the kits is that it uses some pretty coarse grits on some of its stones. 70x is incredibly coarse, something that you would find on a motorized grinder to shape a heavily damaged blade, same with the 120x. You could really make a mess of a good knife with those.

      • P161911

        Thanks for the info. Just wanted to make sure they weren't in the same category as the electric sharpeners.

  • skitter

    For a minute, I was doing the lady/vase thing with the depictions of different edges, and was wildly confused. Sorted now. Carry on.

    • The Professor

      That got a chuckle;)

  • So much build up and so little sharpening! I can't take it!

    This is useful information, I look forward to the next installment!

  • craigsu

    Thankfully, turning tools don't require a tremendously fine edge. I sharpen all of mine on my Porter Cable 3 x 21 belt sander. Just flip it upside down and clamp it in the tail vise of my bench at about a 25-degree angle and sharpen away. If I need to regrind a bit I use 80-grit; if I'm honing I'll use 120-grit. Just before a finish cut I'll use my pocket diamond stone to remove the coarse burrs. This little step prevents a lot of sanding. I've tried a few jigs on grinders (David Ellsworth's bowl gouge jig, for example, is a good one, along with the Oneway Wolverine system) but it's easier for me to just do it by eye. If you think you're going to screw up an expensive gouge, just buy a piece of tool steel and practice first to get your coordination down.

    For my wood chisels I definitely use my diamond stones and cut a secondary bevel. I also make certain I polish the flat back edge. The inexpensive honing guide that Woodcraft sells (http://www.woodcraft.com/Product/2003114/576/Honing-Guide.aspx) is more than adequate for getting a proper angle and works well for hand plane irons, too. It's routinely on sale for $9.99.

    • craigsu

      Ah, yes, the ProEdge.  A fancy $500 version of my belt sander.  Your budget is obviously bigger than mine.  I use the Porter Cable because I don't even have a grinder.

      • craigsu

        Now, now, don't you go getting defensive on me.  I'm a dyed-in-the-wool capitalist, so I will never begrudge anyone who has the means to spend their hard-earned money however they wish.  And I appreciate value for dollar in tools (I own a Oneway 2436 lathe, remember?).  My tool budget has been virtually non-existent for some years now so, necessity being what it is, I've had to come up with alternate methods.The ProEdge is a fine tool and it, along with other various jigs, has been a boon to older woodturners in particular.  Even at 50 years old I'm still one of the youngest turners in the room at meetings.  For folks who have issues with fine motor control these jigs are a godsend.  I remember attending one of Rude Osolnik's last seminars, before he was bedridden.  His day nurse had to help him get to the lathe and we all held our breath when we saw how much his hands were shaking.  As soon as that metal touched wood, however, decades of muscle memory took over and he attacked that piece with surgical precision.  I'm sure, however, that he wasn't sharpening his own tools at that stage of life.Preach on, brother!

  • MrHowser

    Nice! I'm looking forward to this series. We got a very nice set of J.A. Henckels knives for our wedding in '09, and use them every day. They're very much due for some maintenance, but I've been hesitant to tackle the sharpening for fear of ruination.

    • The Professor

      Henckels makes very good knives too, and you want to take care of them. With luck, I should be able to give you some pointers.

  • <img src="http://1.bp.blogspot.com/-Fmkp8citOqs/TeIOkhVPhiI/AAAAAAAABco/GEdLYJn1th8/s1600/carving-tools-sharpening.JPG&quot; width="250">

    OH. Now I get it. Rotating abrasive wheels can also be used to sharpen edges. Clever. Now if only there were some way to bring it into contact with that wheel on the ground….

    • The Professor

      Weirdo.

  • BlackIce_GTS

    Oh good, now I can learn to make my collection of cheap pocket knives less laughably dull. And maybe those terrible katanas a friend gave me, but I don't have much hope for them.
    There's a bewildering array of sharpening apparatii available, and it would be helpful to be pointed in some direction or other.

    • texlenin

      That was a cutting remark…..

    • The Professor

      I plan on covering several methods of sharpening, from bench stones to motorized sharpening systems. There should be something in there that will work for you.

  • I found this very informative and useful

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