Thinking about steels

On 2014-10-04 08:57, scott grandstaff wrote:
[Quoting James Thompson]
> It works quite well.
>   https://picasaweb.google.com/102358420595488787966/KnifeSteelSmooth
?authuser=0&feat=directlink">https://picasaweb.google.com/102358420595488787966/
KnifeSteelSmooth?authuser=0&feat=directlink
>
>    The steel is interesting. It must have worked more like the single
> tooth scrapers they make Japanese swords with.
>   Or a 4 sided reamer, like a birdcage awl.

The smaller the radius of the corner, the greater the force per square 
inch on the knife bevel. The greater the force the more damage you do to 
the knife.

A smooth steel would have the largest radius, various types of ribbed 
steels much smaller radius except that often two ribs would be in 
contact with the bevel.

This steel has the radius of a very thin wire.

The knife sharpening gadgets Dick sells - you push the knife down 
between two spring wires (perhaps with some abrasive coating) - the 
depth determining the angle and presumably being different every time 
you use it - has small radius hones but larger than the radius of the 
corners of Jim's steel.

However, all these radii are much larger than the abrasive particles on 
conventional abrasives. The effect on the steel is as if you use a 
single large abrasive particle that has a cylinder shape in the 
direction of motion.

Very fine abrasives, in the micron range (a few orders of magnitude 
smaller than any of these steels, even those with small radii like 
Jim's), are able to remove metal with almost no damage to the crystal 
structure of the steel.

A sheet abrasive, where many thousands of abrasive particles would be in 
contact with the bevel at any time, has several orders of magnitude less 
force per particle.

Forming a bevel by pushing the metal around - using a knife steel - 
affects the crystal structure about the same as stretching the metal to 
20 times its heat treated length. It can be work hardened but its 
durability is compromised.

All that is before you even get to the freehand sharpening question.

Brent
-- 
Brent Beach
Victoria, BC, Canada