Greetings:
Here is some info about sharpening chopper blades:
http://www.tech-mark.com/sharpen.htm
http://www.tech-mark.com/morsochopperinfo.htm
So these folks advocate hollow ground blade sharpening. They say it is what is recommended by the manufacturer.
I tend to believe that a hollow ground blade is sharper. Sharpness is due to the thinness of the edge. A flat ground blade at 30% vs. a hollow ground blade at 30% can not physically be thinner and therefore not as sharp. However, does it really make a difference? I don't know. Maybe flat ground is sharp enough.
Durability? I would tend to agree that flat honed blades should stay relatively sharper longer since the edge is thicker. I am not sure why the manufacturers recommend hollow grinding.
Okay. Heat? Annealing the blades through use? Baer. You must be one hellofa chopper **** if you can heat your blades up to the point of rendering the metal!
Annealing is used to cause the metal to be less brittle and more workable so it can be more easily shaped while cold. It is a heat treatment process whereby the metal is heated to extremely high temperatures and then slowly cooled in a controlled manner in order to cause the atoms to settle into certain patterns and structures. This creates a soft structure and large grains with poor toughness.
Once a metal is worked or machined, it is then normalized. Here the metal is heated and then allowed to cool relatively quickly in air creating fine grains with uniform structure.
The metal is then tempered. Carbon is released from the nucleated areas, allwoing the sturcture to deform and relieve some of the internal stresses. This somewhat reduces hardness, yet increases toughness.
So... I really don't believe that the metal, even the micro fine edge of the blade will acutally become softer with use of the chopper. Yes, it could and does become dull, but this is not really due to extreme heat and annealing, rather simply reshaping of the micro edge through blunt trauma. Minute particles of the sharp edge are deformed and reshaped each time the blades strike the moulding.
So is the jury out? Do we really want our chopper blades to be flat or do should we be having them hollow ground?
I like your Mirror story!
Warmest aloha,
Bill