Sunday, January 8, 2012

Sharp Conversation

After dinner she put down her glass and looked over to me, “How often should I sharpen my knife?”

I looked at her and then over to my wife.  We had just finished dinner and I was sharpening our guest’s pocket knife at the dinner table.  Clearly some sign was needed before I carried on.  I got it.

“If you wait until it’s dull, you’ve waited too long.  It’s always easier to touch up an edge than to bring a dead edge back to life.”  

“What about electric sharpeners?”  She asked a good question and I had half an answer.

“Depends.  Some people press too hard, leave it in contact with the rotating stones too long and heat the blade up too much.  That will damage it.”

There’re really only a few things to remember about tempering and steel.  Tempering is actually a softening step.  The martensite that forms from austenite can make steel so hard as to be unusable.  Tempering allows other softer structures to form and make the steel usable.   Too much tempering, too soft to hold a good edge.  Too hard and the blade snaps too easy.

Almost all the structures that give steel its incredible properties are diffusion based.  Diffusion is driven by time, temperature and moderated by distance.  Heating a knife blade at the thin edge will affect the steel more than heating the spine the same amount.  And the effects of heat cycles are cumulative. 

So how often should you sharpen and how?

I believe you should sharpen when the edge seems to be getting dull.  If you’re butchering a deer you may want to touch the blade up often.  If all you do is cut string and open paper envelopes, you can go a long time.

In the kitchen you should touch up the blade of your chef’s knife before you use it.  The sharpening steel doesn’t sharpen the edge, it draws the wire edge out.  That’s a good thing, as the wire edge is the really the source of sharpness.
You’ll find it easier to keep a sharp knife sharper than resharpen a dull knife.  And I learned that the hard way.

Last summer was a time for “trench warfare.”  I was running underground cable to my soon-to-be-built garage.  After it was up I got a lot of help from my friend Rick with wiring the garage.  With all the cutting and trimming my favorite work knife, a CRKT Crawford Kasper folder, became very dull.

How dull?

So dull it refused to cut anything.

I could have taken it to a professional sharpener and had it re-edged, but as penance and hard luck lesson, I resharpened it myself with my Spyderco sharpener. 

Spyderco Sharpmaker

 I’m still working on it.  I get it sharp, but as soon as I need it for some job it slides toward dull.  I haven’t been able to spend enough time to push it from sharp to very sharp, which is where I prefer my knives.

I also use the Lansky system.  The ability to hold each progressively finer grit stones at the same angle is a gift from the knife gods.   
Lansky system





The downside: it’s a lot of work to set up properly just for a little touch up.

Benchstones. I’ve got more than a few.  The key to good benchstone sharpening is reproducibility and cleanliness.
Gunk up the natural pores in the stone and it will not sharpen.  So use a good oil and clean it off when you’re done.

Holding the knife edge to the same angle through each stroke is critical for a sharp edge.  We can all get better at it, but some people are gifted at it.  I’m not one of them.

Years ago I bought a Buck Honemaster to help me sharpen my knives.  
Buck Honemaster  You can see a dull strip of metal towards the edge sitting on the wood.  That's metal wear from sharpening blades.


 It clamps on your blade and holds it at the angle you select.  The angle isn’t very reproducible between sharpenings, but you can get a fine edge with it.  Of course, as you wear metal from the knife edge, you wear metal from the Honemaster.   It’s a strange sensation knowing you’re destroying the means of making a great edge while you’re making a great edge. 

Buck Honemaster holding my Commando Cutlery on the fine side of a benchstone

On the whole, sharpen your knives before they get dull.  They’ll work better, faster and easier.  A sharp knife reflects well on its owner.

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