Super Extreme sharpness experiments?

[DennisStrickland]

i had a neighbor whom is a retired german barber work on my spyderco m4. he got it so sharp that when it is waved in air you can hear molecules scream trying to get out of way.

 

[Ankerson]

Just 3 words.

Air Bleeding Sharp.

 

[Joshua J.]

I was just thinking about the math/physics behind this. .1 microns is 3.937x10^-6 inches. So if your edge is that thin, and you apply one pound of pressure, then you're applying ~3,937,000 pounds per square inch with the edge on whatever you're cutting. No wonder it cuts!

Oh yeah, I don't put less than 20 included degrees on any of my blades, but I can pop hair pretty well. Besides for proper shaving purposes, is there any marginal gain in utility going that thin/sharp?

I got pretty excited the day I realized the mechanics behind cutting. It is a very cool concept.

What's a zero edge?

That's where the primary grind forms the edge. In order to sharpen it you just lay the knife flat on the stone (if it's a full flat grind).

While it is very cool to have an edge so thin that you can visibly flex it side to side with your fingernail, it doesn't work well with every steel (Rc60 and higher is necessary IMO) and is not very durable at all. Once you put a ten degree per side microbevel on that zero edge, then you have a very nice working blade.
If you measure in terms of edge thickness (with the micro bevel) that's between .002" and .004" (I usually just round up to .005"). Most knives come with an edge thickness between .025" to .035".
Edge thickness is usually measured at the shoulder where the primary grind and edge grind meet. If the blade is coated it's easy enough to see, with the edge being shiny metal color and the rest of the blade being the coated color.
As mentioned, a true zero edge will be measured in microns, and is theoretically determined by the grit you use to sharpen.