How do things dull?

[Gary Keedwell]

http://www.dixmetals.com/NewsEvents/...FQQfgAodSVRY1A

Another one here.

Gary K.

[Eddie Darby]

If the metal has perfect bonds at the atomic level, then dulling would be a lot harder, but this is not the case. Metals contain what is called dislocations, which is a mis-alignment in the atom matrix.

This leads to a weakness in the metal that causes stresses to gather around. Get enough stress in that area, and you get more dislocations. More dislocations make for dulling when a piece falls off.

Just like a crack is a mechanism that focuses stress and concentrates it in one small area, a dislocation is a very small small small crack, which just happens to be very very good at concentrating stress. The smaller the better.

When blades are cryo frozen, it is in hope that the slowed down vibrating metal atoms will form more bonds, and thus last longer between sharpening because there are fewer dislocations.

[Lynn Sonier]

Intriguing thread, guys. Very informative.

[Bill White]

I'm gettin' a headache. Too much dulling effect I guess.
Bill

[Gary Keedwell]

I'm getting a headache, too. I think it is because I'm a dullard.
Gary K.

[Rich Engelhardt]

Hello Pete,
Sharp edges curl over with use and appear dull.
A steel (such as a butchers steel) or a ceramic rod (like the Spyderco Sharpmaker - straighten the edge back into it's normal position.

Soft material such as wood or paper or cardboard turn the wafer thin edge down - they don't really wear away at it.
Here's the rub though. Once the edge has curled over, continuing to use it will "push" the thin edge down even harder.
Kind of like folding a piece of paper over then running your finger across the fold to realy set it down.
When you do that to steel, then try to straighten it, the thin edge (called a burr) can snap off.
Or - it can simply snap off itself from the pressure of being folded too tight.

There's a plethora of posts here where people report a joiner or planer blade getting a nick in it and swear to high heaven they did't hit anything hard duing the course of their work. My bet would be the burr edge simply folded down too hard and snapped off.

IMH - estimate 98% of steel edges are sharpened by needlessly removing material when all that's really needed is for the edge to be curled back to it's proper position.
That's all well and fine for a double bevel like a typical knife has, but not so practical for a chisel grind where the back edge needs dressed.
it's also not practical for the edges on saw teeth - or for most other (power) tool type blade applications.

Do a google search for the name Joe Talmadge.

Joe is to sharpening steel as Jeff Jewitt is to finishing and finishing materials. I've followed Joe's posts on several knife and custom knife forums for close to 10 years, and for a few years prior to that on the old news group alt.rec.knives.
He's written a lot of essays, magazine articles - and I believe he may have written a book on the subject also.