There’s a common belief that you can keep a knife sharp for a year or more by using a rod hone aka “knife steel.” WRONG-O!
All knives get dull. There’s only so much you can do with a steel. This isn’t just about my standards of sharpness, but everyone’s.
• A fine or polished steel will true a bent edge but won’t restore one which is worn.
• A medium, coarse, or diamond steel, will create a coarse edge and an uneven bevel. While the knife will cut, it will cut more like a saw than a knife.
A CTer argued that one can use a steel to keep the knife sharp and prevent it from ever getting dull or needing more aggressive sharpening. It occurred to me the subject of dulling itself -- what it is and what to do about it -- can use a little demystification.
Q. How does a knife get dull?
A. All work and no play.
Okay, with that out of our systems we can move on to three real phenomena, deformation (bending out of true), corrosion and wear.
Think Knife Thoughts:
Before we get into this, start by visualizing the cross section of a properly sharpened edge as a V.
The cross section of a rolled or waved blade can be compared to a y.
Edges bend from impact. More often than not it’s impact against the board, but sometimes it comes from cutting through anything hard. Cutting through bones will do it nearly every time.
Bent edges are commonly described as “rolled.” That can be refined somewhat into waving and rolling. While the difference is only a matter of degree, it’s significant as a practical matter. A waved edge (my term, and not universal) isn’t pushed over as far one which is rolled. If you’re visualizing the cross section as a “y”, roll or wave depends on the degree to which the tail is bent.
The practical part of the distinction comes in the mending. Assuming there’s not too much asymmetry or the knife alloy isn’t too hard – it can be easily repaired with a few passes on a rod hone (aka “knife steel”) which trues the edge.
The further the edge is rolled, the more truing it weakens it. And an edge which is rolled beyond a certain point won’t straighten on a steel, instead it will fold over further. This means treating severe rolls as you would a chip and sharpening them out.
A steel is not the be all and end all of sharpening.
Carbon alloys are more reactive than stainless alloys and consequently are far more prone to corrosive blunting. Reactive alloys blunt in a couple of ways.
Passivation (not really corrosion, but what are you going to do?) forms deposits on the surface. In his essay Knife Sharpening Experiments, John Verhoeven describes “Debris Deposit burrs.” You can visualize the cross section of an edge blunted in this way as a U
Actual corrosion, e.g., rust, eats away at the metal and weakens it causing it to break very easily. The breaks give the knife a toothy, WWWWW profile (not cross section). In addition to the other undesirable aspects of too much micro-serration, the edge is inherently weak. Each tooth is subject to bending or breaking.
Frequent steeling will keep the metal fresh and relatively free from corrosion. But, even a polished or ultra-fine steel will scuff up the bevels, and the edge itself – creating (you guessed it) too much micro-serration.
The best practice – and again this presumes knives which can be profitably steeled – is to use a fine, ultra-fine, and/or polished steel as frequently as necessary; and going on to bench stones, an Edge Pro, or other abrasive method as soon as necessary to keep the knife very sharp.
Wear is simply erosion by another name. In the same way water flowing over a stone eventually rounds it by removing material grain by grain and wearing away the edges, so normal use wears down the edge – which you’ll be kind enough to remember is very thin as a result of sharpening.
Please visualize the cross section of a worn edge as a U, just like a debris deposit burr.
The only solution is to sharpen using proper sharpening gear appropriately. What “proper” and “appropriate” mean is a very long subject in itself.
Just to kick the subject off, sharpening means using an abrasive to create an appropriate shape while revealing fresh metal. While you can true an edge, and even scuff it up enough to give it a little bite with a fine to polished rod hone it does not actually sharpen.
Because their narrow contact areas create so much force and because their aggressive surfaces remove blade material so quickly medium steels, coarse steels, “diamond” steels, or any carbide sharpener, etc., are not appropriate for sharpening good knives.
PS. A substantially similar version of this post is on my blog.
Edited by boar_d_laze - 10/20/10 at 10:48am