Managing expectations of edge retention

D

DevinT

Joined
Jan 29, 2010
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There is a lot of talk about edge holding/retention by knife enthusiasts. In general, edge holding is over hyped leading to disappointment.

I hear lots of makers talk about how they have discovered the secret to heat treating and produce a knife that will hold an edge forever.

A very keen edge is sharpened to an apex of ~.4 microns. Edge holding is the measure of wear resistance at the apex. The edge starts to feel dull after the edge wears to >2 microns.

All steels wear when used and will require resharpening, even Rex 121.

No amount of thermal cycling, forging, quenching, or sharpening will change the fact that every edge will wear in use.

The harder the matrix, the longer it will hold an edge.

The harder the carbides and the higher the volume of carbides, the longer it will hold an edge. (This is determined by the composition of the steel)

The coarser the sharpening grit used, the longer it will hold an edge. (still requires a very fine radius at the apex)

The thinner the grind, the longer it will hold an edge.

The more acute the sharpening angle, the longer it will hold an edge. (the matrix must be able to support the edge)

I’ve heard people claim that the knife can process a big zillion deer without sharpening, what they don’t tell you is that they constantly touch it up with a strop or a hone thinking this is different than sharpening.

Sharpening is part of knife maintenance and I think we should talk more about it. Once a person learns to sharpen, it doesn’t take long and is part of the fun of knives.

Hoss
 
What I have come to realize is that many in the knife collector community have so many knives that they rotate into use that their knives see only occasional use every few months. These people will then swear how certain steels perform and go on about how only stropping is needed for a life time of knife maintnece.

Another group of people are those that use the few knives that they have but never sharpen them and just live with dull knives.

I often talk customers out of using certain steels after discussing their sharpeing skill level. My thought is why sell a knife to person who lacks the skills to maintain the tool when there are other steels that are easier to maintain.
 
The idea is to get the blade red hot before attempting to sharpen. That way, you are just pushing the molecules around to form an edge rather than removing molecules. The goal is to refine the apex to the width of one molecule. Then lock in the molecular structure by quenching it into an all-dressed potato(hold the chives). I feel the need to drive this home by saying "molecules" one more time.

Heh heh... Good post, Hoss. Most users, judge the quality of a knife by it's sharpness, edge retention and the type of steel it is made from. All of which mean nothing if the maker doesn't have an intimate knowledge of the mechanisms that govern those attributes. I will add my bit of advice.....

I cannot stress enough the importance of keeping that edge cool while sharpening. Lube, coolant, quality abrasives.... all will reduce heat build-up. Even hand sharpening on a dry diamond plate can overly temper the apex. This became surprisingly apparent to me, when I started making kitchen knives. I was a "220 belt, cork belt strop" guy when I was making choppers and camp knives. They were crazy sharp but I did not realize how much edge retention I was leaving on the table by my method. When I switched to setting my final edge with water stones and CBN plates (with plenty of water), I felt embarrassed.... don't tell the other guys, K?
 
Rick Marchand said:
The idea is to get the blade red hot before attempting to sharpen. That way, you are just pushing the molecules around to form an edge rather than removing molecules. The goal is to refine the apex to the width of one molecule. Then lock in the molecular structure by quenching it into an all-dressed potato(hold the chives). I feel the need to drive this home by saying "molecules" one more time.

Heh heh... Good post, Hoss. Most users, judge the quality of a knife by it's sharpness, edge retention and the type of steel it is made from. All of which mean nothing if the maker doesn't have an intimate knowledge of the mechanisms that govern those attributes. I will add my bit of advice.....

I cannot stress enough the importance of keeping that edge cool while sharpening. Lube, coolant, quality abrasives.... all will reduce heat build-up. Even hand sharpening on a dry diamond plate can overly temper the apex. This became surprisingly apparent to me, when I started making kitchen knives. I was a "220 belt, cork belt strop" guy when I was making choppers and camp knives. They were crazy sharp but I did not realize how much edge retention I was leaving on the table by my method. When I switched to setting my final edge with water stones and CBN plates (with plenty of water), I felt embarrassed.... don't tell the other guys, K?
Click to expand...
Sir I have missed your humour in these parts! Glad to see ya a round again now and then.

Hoss great post!
 
DevinT said:
There is a lot of talk about edge holding/retention by knife enthusiasts. In general, edge holding is over hyped leading to disappointment.

I hear lots of makers talk about how they have discovered the secret to heat treating and produce a knife that will hold an edge forever.

A very keen edge is sharpened to an apex of ~.4 microns. Edge holding is the measure of wear resistance at the apex. The edge starts to feel dull after the edge wears to >2 microns.

All steels wear when used and will require resharpening, even Rex 121.

No amount of thermal cycling, forging, quenching, or sharpening will change the fact that every edge will wear in use.

The harder the matrix, the longer it will hold an edge.

The harder the carbides and the higher the volume of carbides, the longer it will hold an edge. (This is determined by the composition of the steel)

The coarser the sharpening grit used, the longer it will hold an edge. (still requires a very fine radius at the apex)

The thinner the grind, the longer it will hold an edge.

The more acute the sharpening angle, the longer it will hold an edge. (the matrix must be able to support the edge)

I’ve heard people claim that the knife can process a big zillion deer without sharpening, what they don’t tell you is that they constantly touch it up with a strop or a hone thinking this is different than sharpening.

Sharpening is part of knife maintenance and I think we should talk more about it. Once a person learns to sharpen, it doesn’t take long and is part of the fun of knives.

Hoss
Click to expand...
Yeah … i have a Petty with a VG10 core that i have not needed tosharpen in something like five years … and also have a Nakiri with a Hitachi White core that i need to touch up something like once a week.

Must be bad steel or bad HT on that Nakiri.

…..on the other hand, i very seldom use the petty, and reach for that nakiri multiple times a day, every day.

Must be something substandard about that nakiri…
 
Edge retention is resistance to abrasive wear.
Edge holding is resistance to plastic deformation due to force or pressure.
Not the same.
 
Rick Marchand said:
The idea is to get the blade red hot before attempting to sharpen. That way, you are just pushing the molecules around to form an edge rather than removing molecules. The goal is to refine the apex to the width of one molecule. Then lock in the molecular structure by quenching it into an all-dressed potato(hold the chives). I feel the need to drive this home by saying "molecules" one more time.

Heh heh... Good post, Hoss. Most users, judge the quality of a knife by it's sharpness, edge retention and the type of steel it is made from. All of which mean nothing if the maker doesn't have an intimate knowledge of the mechanisms that govern those attributes. I will add my bit of advice.....

I cannot stress enough the importance of keeping that edge cool while sharpening. Lube, coolant, quality abrasives.... all will reduce heat build-up. Even hand sharpening on a dry diamond plate can overly temper the apex. This became surprisingly apparent to me, when I started making kitchen knives. I was a "220 belt, cork belt strop" guy when I was making choppers and camp knives. They were crazy sharp but I did not realize how much edge retention I was leaving on the table by my method. When I switched to setting my final edge with water stones and CBN plates (with plenty of water), I felt embarrassed.... don't tell the other guys, K?
Click to expand...
I have a few Wildertools, and just have to say that they will hold an edge forever! He said something about voodoo, and edge packing but I never deigned ask what he meant. Now I understand- it's all about the potato!

I love sharpening knives, can't not do it- even with fancy customs that don't get used. It's a sickness, and that's why I'm here- group therapy!
 
I appreciate Hoss' post.

I struggle to figure out why so many people don't take the time to sharpen their knives.
They're about 20-40 bucks and a little dedication away from having a safer, more pleasurable cutting experience.

The one that really hurt was when my in-laws, against my best advice, bought a Cutco set.
My mother in law told me once that she was dissatisfied with her current kitchen knives.
👨"When did you last have them sharpened?"
👩"They've never been sharpened."
👨"Oh, well how long have you had them?"
👩"Maybe 20 years."
🤦‍♂️
Well needless to say, the serrations on the Cutco knives have given up the ghost in these past few years.
They don't want to send them away to Cutco, for whatever reason, so they want me to sharpen them.
I could have just sharpened their original set and saved them 500 bucks.
Cutco's salesmanship has won the day, and it makes me sad.

... and that's not even the latest and greatest steel or knife-enthusiast salesmanship.
 
JoeBusic said:
Ad-hominem is a sign of weakness and incapability.
Live to learn and prosper.
Click to expand...
Ad-hominem is actually a logical fallacy, so by implying the other person is weak and incapable, you're returning the favor.
You can cut an argument a lot shorter by citing your sources for the definition of edge holding vs. edge retention.
Pun very much intended.
 
There are three basic types wear, abrasive, adhesive, and corrosive.

Adhesive wear could apply to shears, scissors, or moving parts on folding knives.

Plastic deformation is not something most knife users or buyers worry about, they trust the maker/manufacturer to select the right steel and heat treat for its intended purpose.

Hoss
 
JoeBusic said:
Edge retention is resistance to abrasive wear.
Edge holding is resistance to plastic deformation due to force or pressure.
Not the same.
Click to expand...
I have never seen the term "edge holding" used to refer to plastic deformation before. Edge retention has been used interchangeably with edge wear, I am as guilty of that as anyone, though perhaps the more universal definition is simply the ability to maintain sharpness, regardless of the mechanism involved for dulling.
 
Larrin said:
I have never seen the term "edge holding" used to refer to plastic deformation before. Edge retention has been used interchangeably with edge wear, I am as guilty of that as anyone, though perhaps the more universal definition is simply the ability to maintain sharpness, regardless of the mechanism involved for dulling.
Click to expand...
I accept Dr. Thomas as an authoritative source.

JoeBusic JoeBusic I await your reply with your sources.
 
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