New Posts  All Forums:Forum Nav:

Dulling Thoughts

post #1 of 21
Thread Starter 

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. 

 

Consider:

    •    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?

Psycho_Betty_Kitchen_Knives.gif

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.

Bending:
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.

Corrosion:
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:
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.  

 

BDL

 

PS.  A substantially similar version of this post is on my blog.


Edited by boar_d_laze - 10/20/10 at 10:48am
post #2 of 21

BDL,

 

I've watched a few knife sharpening videos and some on steeling.  I'm left with one huge question.  Do YOU sharpen with the edge/bevel/whatever being pushed/pulled into the stone (cutting in) or do you sharpen with the edge being dragged across the stone/steel?  I know that doesn't make too much sense, so if you were to try, during sharpening, could you cut a chunk out of the stone (or do you drag the edge so that the stone can only cut the edge)? 

 

When steeling, do you push the edge into the steel or drag it across?  If you push into the steel, I can see how an edge could roll over worse (double back on itself) but if you pull, it seems like you run a much better chance of straightening the "roll" out. 

 

If you use the "cutting into the stone" method, can you explain why it is better than the reverse method?  It seems like you run the risk of creating more wear on the stone and getting worse results in actual sharpening. 

post #3 of 21

I just wanted to say BDL looks very nice in that picture. Back to the dull discussion.

Anulos qui animum ostendunt omnes gestemus!
Reply
Anulos qui animum ostendunt omnes gestemus!
Reply
post #4 of 21

Good 'un, Greg.

 

Boar, you should point out that waving is not always even, and the deformed edge can, if magnified, resemble a greatly opened up S.

They have taken the oath of the brother in blood, in leavened bread and salt. Rudyard Kipling
Reply
They have taken the oath of the brother in blood, in leavened bread and salt. Rudyard Kipling
Reply
post #5 of 21

I'm not a fan of this page I'm going to link to. However, it has some very interesting pictures that merit further discussion. These are magnified photos of a knife edge. Spyderco posted some better ones at higher magnification at some point but my google-fu is not sufficient to find them today.

 

http://sharpeningtechniques.blogspot.com/2009/12/micro-photos-of-identical-knives-after.html

Palace of the Brine -- "I hear the droning in the shrine of the sea monkeys." Saltair
Reply
Palace of the Brine -- "I hear the droning in the shrine of the sea monkeys." Saltair
Reply
post #6 of 21
Thread Starter 

Gobbly,

 

You're sure as heck not the first person to ask, and there are a lot of other people who have the same questions.  They come up all the time.

 

Do YOU sharpen with the edge/bevel/whatever being pushed/pulled into the stone (cutting in) or do you sharpen with the edge being dragged across the stone/steel?  [...] If you were to try, during sharpening, could you cut a chunk out of the stone (or do you drag the edge so that the stone can only cut the edge)? [...] If you use the "cutting into the stone" method, can you explain why it is better than the reverse method?  It seems like you run the risk of creating more wear on the stone and getting worse results in actual sharpening.

 

It's always sort of crummy to start with technical terms (or jargon, if you prefer), especially with sharpening where they can be extremely ambiguous.  But since a lot of things will probably come into better focus, let's do it anyway. 

 

"Honing" means using an edge leading, spine trailing motion.  That is, with the edge cutting into the stone.  Stropping means using a spine leading, edge trailing motion.  

 

With that capital YOU, I'm guessing you meant me.  I've tried just about everything, but currently I'm using a mixed bag of tricks and techniques.  On my coarse to medium fine stones, with the exception of deburring, I hone and strop, up and down the stone.  I almost "section," when I do that, which means sharpening one (overlapping) stone's width of the edge at the time.

 

Once the burr is refined enough to flip easily, I start deburring using honing strokes with each stroke going length of the blade, always from heel to tip.  I usually do this as 5 strokes on each side, and flip; then 3 strokes on each side, and flip; then 16 strokes total (8 on each side), alternating sides with each stroke; then deburr -- usually in a wine cork.

 

But sometimes, I'll skip most of that and run the knife down a honing rod (aka "steel") a few times to loosen up the burr before going to the cork or whatever else I'm deburring with. 

 

I start polishing with the up and down motion, but with very little pressure so as to avoid drawing a burr.  Because the bevel is (or should be) already perfected and doesn't need sectioning, I use a fair bit of lateral motion as well.  After briefly polishing both sides that way, I check for a burr and deburr if necessary.  I finish polishing the knife with full honing strokes alternating sides with each stroke.  Even though there's almost certainly no burr at all, more often than not I'll run the edge very lightly on a cork, "just in case." 

 

After polishing, try and keep the knife away from a rod as long as possible.  No matter how polished the rod, it will still rough up a fine edge.  

 

Most sharpening stones are hard enough that you can't actually cut into them; but there are a few exceptions.  The way to avoid cutting into the stone, damaging it and risking damage to the knife is to hold a very steady and very appropriate angle.  But nobody's perfect, and sharp knives do gouge soft stones.  If the thought bothers you, it's easy enough to avoid those stones. 

 

When steeling, do you push the edge into the steel or drag it across?  If you push into the steel, I can see how an edge could roll over worse (double back on itself) but if you pull, it seems like you run a much better chance of straightening the "roll" out.

 

We've already established that "steel" is the nickname for a honing rod.  Always hone.  Never strop.  Ideally you should lay the knife on the hone at the exact same angle as the bevel -- the same at which you sharpened.  If you angle the edge into the steel, you'll scuff the edge. If you hold the knife too flat, you won't get anything done.

 

You often see cooks (and not just on TV either) rushing the process using too much pressure, using way too many strokes, and banging their knives on the hone.  Mais non!   After you've done it a few hundred times your speed will come up tremendously, but you'll never outgrow the need to slow yourself down.  At least I haven't.  If you want to know more about steeling, follow this link.

 

On strops -- which you didn't ask about -- it's the reverse.  Always strop, never hone.

 

Hope this helps,

BDL 


Edited by boar_d_laze - 10/17/10 at 7:35pm
post #7 of 21
Thread Starter 

KY -- Excellent point, but no need for me to do it since you already did.

 

Phatch -- The sharpneing mavens here must be smart fellas (wait did I say that right?  Smart fellas?  Yes. That's right.  Smart fellas) since we've been rating the different sharpening methods just the way the pictures showed them. 

 

BDL

post #8 of 21
When watching TV cooking shows it drives me nuts every time I see a chef use the cutting edge of the knife to scrape food across the cutting board. That can't be doing the knife any good and it is like fingernails on a chalk board. I will stick to sharpening on my edge pro and I hone on a ceramic stick.
post #9 of 21
Thread Starter 

Hi Mary,

 

The idea behind this thread was to argue against the idea that using a rod hone is a total solution as at least one CTer argues, because where's there's one, there's usually many.  A survey of sharpening systems was never intended.  But threads have a life of their own, and you make a good point.  Since you have to sharpen anyway, you may as well do it well.  Edge Pros are certainly among the few very best ways to go about it. 

 

BDL

post #10 of 21

BDL, what are your thoughts on wicked edge?  Looks like a great, but overpriced idea.

post #11 of 21
Thread Starter 

Originally Posted by gobblygook View Post 

 

BDL, what are your thoughts on wicked edge?  Looks like a great, but overpriced idea.


Never saw one in person and haven't even heard enough to have an uninformed opinion.  It would be nice to hear from someone who has experience with both it and both of the Edge Pros. 

 

The video indicates that there might be some limitations.  The most acute angle you can set seems to be 15* -- which isn't terribly acute.  Another issue is that it's pretty expensive to even get to a 3u grit -- the equivalent of 4K (JIS) -- which isn't a particularly fine polish. 

 

BDL

post #12 of 21
Thread Starter 

Give it a while and simple thoughts can penetrate even the hardest of bone heads.  The raison d'etre for this thread was never clearly expressed.

 

I'm editing the original post as well as the parallel post on my blog to include the following:

 

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.

 

The rest of the post makes a lot more sense with that at its head.

 

BDL


Edited by boar_d_laze - 11/13/10 at 12:49pm
post #13 of 21

I caught "modern marvels" recently where they had "world's sharpest" items.  The knife company featured was Cutco.  They had an interesting thing to say about serrated knives is that they don't dull because the cutting edges are recessed and the edge damage is done by contact with cutting boards and such.  Thus the points are the only part dulled and therefore the cutting edges are saved from damage.  Aside from that, their segment was quite interesting, showing the sharpening phases of the knives. 

post #14 of 21

 

Quote:

Originally Posted by gobblygook View Post

I caught "modern marvels" recently where they had "world's sharpest" items.  The knife company featured was Cutco...   

 

 

 

 

They lost me right there.

 

"We make our food; thereafter, our food makes us." - Winston Churchill (with a slight modification)
Reply
"We make our food; thereafter, our food makes us." - Winston Churchill (with a slight modification)
Reply
post #15 of 21
Thread Starter 

It's true, serrated edges don't need sharpening as frequently. A serrated edge isn't sharp in the same way a fine edge is, nor do they cut in the same way.  A serrated edge is essentially a saw and tears a wide kerf more than it cuts a fine one.  As I understand it, a fine edge does something like that at the microscopic level -- but the microscopic level is really the point. 

 

A really sharp knife "falls" or "drops" through vegetables.  Get them sharp enough and you have to apply a little reverse pressure to keep them from cutting because their own weight will take them all the way through to the board.

 

Serrated edges certainly have their places -- splitting cakes, slicing soft breads, cutting frozen foods, and as disposable paring knives, for instance.

 

How Cutco got the placement is an unexplained "scientific" mystery.

 

BDL

post #16 of 21

Nicely described!

post #17 of 21
Thread Starter 

Hiya Clay.  Great to see you here!

 

BDL

post #18 of 21

That's a nice elk, Clay.

"We make our food; thereafter, our food makes us." - Winston Churchill (with a slight modification)
Reply
"We make our food; thereafter, our food makes us." - Winston Churchill (with a slight modification)
Reply
post #19 of 21

Someone talked me into purchasing a Cutco knife many years ago. It's buried deep down in my tool box to this day. Cutco indeed.

post #20 of 21
Quote:
Originally Posted by boar_d_laze View Post

Hiya Clay.  Great to see you here!

 

BDL

Thank you BDL. It's great to be here.
 

post #21 of 21
Quote:
Originally Posted by tylerm713 View Post

That's a nice elk, Clay.



Thanks tylerm713. That was a really fun hunt.

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Food & Cooking