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Saturday, July 16, 2011

Why your new knife might seem to suck.

So you bought a new knife and you used it a few times, but then you put it away with the tens and hundreds in your collection. It was cool, but didn't seem to hold a good edge very long or stay sharp, but that old crapper fishing/hunting/kitchen knife you use all the time does. How come? The simple answer is because you don't use it.

Commercial knives available today are some of the best in history, even the crappy cheap ones. The reason is the steels used in today's knives are some of the best ever made. The computer controlled foundries are producing higher quality steel with less impurities in greater quantities and therefore cheaper than ever before. So even some of the really cheap crappy knives you pick up have pretty decent blade steel.

Why does my new knife suck though? Because of the grind. Check out this nice illustration at wikipedia. Almost every knife you buy that was mass produced will come with a #3 saber grind because it is the easiest and best grind for all around use that a machine can easily make. It has two precise angles, and blades can quickly be ground to a razor sharp edge. So blame the robots! There is nothing wrong with this, but from looking at the illustration you can see the edge is very thin and can easily be flattened or bent out of shape. Most people continue this grind shape on their knives because they use all manner of angled gizmos to sharpen them. Angled ceramics, electric sharpeners and things you pull along the edge are all designed to keep that straight angle on the blade and give you a razor sharp edge.

If you're satisfied with this, great! keep doing what you're doing. The only real difference is you will be sharpening more often, and your edge is more vulnerable to chipping, but you'll have just as sharp a knife, that's just as useful. If you want more out of your knife buy some type of whetstone. Before the usual exasperation, (OMG! How do I use a flat stone to sharpen things? There might be math involved!) let me assure you there is less math involved than there is with the other sharpening gizmos - it's just the other gizmos have done the math for you. You will have to acquire some skill which will mean practice. I will admit I do still use the gizmos for quick stuff and kitchen knives. What you get with a flat stone is an eventual convex edge. That's #6 on the above chart. The convex edge is just as sharp as the V or saber grind, but it is much stronger and will stay sharp longer, and be less prone to chipping. It's all in the sacred geometry. OH NOES MATH! Relax, it's only in the explanation. The convex edge has much more steel backing the edge. Remember from geometry class? Say it with me, circles are stronger than squares and triangles.

So how do you get one? If your knife came with an edge like that you're in luck, as it was most likely hand ground. If not, you can do it yourself, and you don't even have to work hard at it. How? Use a flat stone when you sharpen things. This is where we get rid of the math. Your human sense of angles is vague. You try to hold the precise angle on the whetstone, but due to human error you wont get it exactly right each time. You will however not quit until it's sharp. Over time you will round the angle that the machine ground at the factory until it becomes convex. This happens a little even when you use the sharpening gizmos as long as you're using them often. That's why the old crappy bait knife and kitchen knife I mentioned earlier always seem to stay sharp.

My dad showed me how to use a whetstone when I was young and I've been practicing ever since. There are plenty of videos on youtube that show how to use a flat stone so I won't go into that here. The problem is in the beginning when you're not so good at it YOU WILL most likely scratch the blade. Start with a knife you don't really care about the finish on until you get the hang of it. Once you get it down you'll have no problems with scratching finishes. It just takes practice and best of all once you get the technique there's nothing for you to do, just keep using the flat stone and you'll get that convex edge. So get practicing!


Alan said...

I don't know anything about whetstones. Is there a particular kind that is good?

Weer'd Beard said...

Sharpening is one of those zen things that I really geek out on.

I'll often bring up a nice stone set and work on Mom's knives while just chatting it up.

Super relaxing, and very satisfying to have a knife that just slides through a ripe tomato.

Chris said...

@Alan There's basically three routes you can go. The basic set is usually coarse, medium and fine. There are also super fine and super coarse but you don't really need them. The general types are diamond whetstones which are inexpensive and last a very long time. They don't require lubrication, but they take off a lot of metal. There's Japanese water stones. Which you wet when you use. They also wear out very fast. The last set you can get are Arkansas oil stones. They come in natural or synthetic and work best when used with mineral oil (baby oil) They are more expensive, but they usually last forever. You can clean them with a scouring pad. I'm not sure if any particular brand is better than any other. If you just want to get started and try it I've seen cheap sets at home depot and lowes that come with 3 stones and some oil. Sometimes you'll see stones listed as tool sharpening stones. They are pretty much the same thing. When you first start out try and get larger "bench" type stones. These are more expensive, but easier to get the hang of things with.

Kirk said...

And then there's the "bored submariner" stone....take your standard government-issue enameled coffee cup. Flip it upside-down (after emptying aforementioned coffee, first...seriously. Don't even go there.). When they pull the ceramic forms out of the mold, they place them on a sheet or something, top-up, and pour the glaze on them. Then they bake the cups and ship them out to the supply system. What results is a ring on the base of the mug where there is NO glaze. Its raw ceramic. And, while standing boring (hopefully...a bored nuke is typically a good thing, means the reactor is working fine) 6-hour under-way watch (or an equally eye-gougingly boring 6-hour port-n-starboard 00-06 Shutdown Reactor Operator watch), one can utilize said raw ceramic ring to put a razor edge on a blade. I used to test mine by shaving hair off my arm to see if it was done. Of course, this takes much practice. To obtain said practice, see your local Navy recruiter.

Heh. I still freak people out occasionally by flipping my huge Stitch (yeah...BEST Father's Day gift ever...a 2-gallon Lilo and Stitch coffee cup) coffee mug over and polishing up my blade.

Old NFO said...

Arkansas stones... period...

Anonymous said...

You can turn knife sharpening into a religion. You will probably only want to sharpen three things a knife, an axe and scissors. Mostly it’s about angles as you have stated and now you can buy sharpeners with the right angles for these tools. The problem I have with the ceramic sharpeners is that you can’t really sharpen the blade next to the handle. I like stones, especially fine grain ones and a drop of oil, pay attention to the edge angle of the tool you’re sharpening and you’re in business. If you want “fast and dirty”, pick up a set of diamond sharpeners at the flee market. They are usually packed three (fine, medium and Coarse) and cost about $5. Use the fine one on knives; use the other two for axes and larger tools. If you do flee markets and you run across a stone that looks promising but has surface scratches or blemishes you can restore the surface if you have a belt sander using a fine grain metal working belt (the dark red/brown ones). Place the stone level in a vise and sand. The best way to sharpen is as you described and if you find that very special stone guard it with your life, good ones are hard to come by.

Jake (formerly Riposte3) said...

I use a Scary Sharp system that I assembled from items at our local craft store. It's simply a flat surface with a fine sandpaper attached.

I use an Elmer's Glue stick and the plastic-backed "abrasive films" on a linoleum printer's block, because the combination means the sheets are easy to remove and reattach when I need to change to a finer or coarser grit.

This system works well enough to get my two straight razors "shave ready", to the point that an accidental twitch can cut me and I won't even notice it until later. If I'm careful, I can get a very close, very comfortable shave. Now I just need a better quality strop.

The Scary Sharp method really lives up to its name, and the whole system cost me about $5. A pack of replacement sheets is only about $1.

Roadkill said...

I am very very lame. I bought a Lanskey croc stick system ( https://lansky.com/index.php/outdoor/4-rod-turn-box/ ), and I am loving it for my stainless blades. Its easy and it works. I like it.

Firehand said...

I've got all kinds of things for sharpening, but what I use most is a diamond sharpener. I use this one:
when a serious amount of metal needs to be removed, and something fine or extra-fine to either finish it off or touch-up something slightly dull.

The good things about the diamond stones is you just use a little water on them, they cut fast and good ones will last just about forever.