On Apr 15, 12:42 pm, wrote:
Brent wote:
the problem with SHARPNESS is it is not a good measure of the
effectiveness of a cutting tool.
For sure, Brent. 
That I would argue is a poor defination of sharpness. I defined
it in the article linked to in the above.
-Cliff
That's true too, like Hob said in response to a knife's ability to
skin out a dead cow.
We are talking past each other tho. :/
My M2 HSS skinning knife has a final edge honing angle of about 5
degrees. That's quite abit more acute than the typical straight
razor. Me and others have used it (and others I've made from power
hacksaw blades) to skin out coyotes and bobcats etc for the fur and
taxidemy business.
We've never needed to do eye surgery, so we haven't realized 65hrc
M2's limits really? 
The whole point of sharpness is the abilty to cut something ain't
it? Whether it's Mike's phone book pages or cutting threads with
a tap.
IMO, every knife knut needs to have at least one 65hrc M2 HSS knife
to fool with. The stuff is amazing, to this simple minded knife
knut anyway.
The fact that M2 is mostly used for metal cutting lathe bits, drill
bits and thread taps doesn't mean it's not good at cutting other
stuff too.
Trying to make my own knives to compete with ~65hrc M2, I ventured
into heat treating 1095 to 66+hrc. Funny how great that stuff is at
cutting into everything except meat. It'll out-cut cold-treated
ATS-34 while cutting meat, but not to the same level of cutting
other stuff. Something about the meat disolving/reacting-with the
plain carbon steel.
Like diamonds don't do so good cutting iron for example.
Either way extra hard, quality steel is easier to get extra sharp
and at an extra acute angle, than soft factory made knives.
So 66+hrc 1095 and 66hrc 8670-modified really kick butt.
Even "soft" ol' 63.5hrc O1 does a real good job.
Obvious as anything... edge angle and blade thickness, especially
right behind the edge all plays a part in cutting ability.
"a knife is a wedge" -long lost r.k'er.
So the trick is to sharpen that-particular-knife to the most acute
angle the steel can handle... doing a certain job, being done by a
certain person.
An old timer's stockman pocket knife will have the three blades
sharpened to different angles for different jobs.
One blade can be at about the same edge angle as a straight razor,
if you have a need for a blade like that.
Cliff's article is very good in defining sharpness and accurate
ways to measure it. I would like to build myself a scale set up,
but after reading about how Cliff used how far away from the point
of hold you can pushcut newsprint I have used that to measure
sharpness. The farther away from the point of hold you can
pushcut the newsprint, the sharper it is (in terms of
pushcutting). I then went to using the yellow pages instead of
newsprint, as I found the results more consistent, though it takes
more sharpness than newprint to pushcut them. Of course, I still
use shaving as a test, and when I have a knife burr free and tree
topping hairs I know it is pretty damn sharp, or at least about as
sharp as I can get it.
Mike
Cool.
Alvin in AZ
ps- I read where SiO2 (flint) is supposed to be only about 58hrc
...is that right? :/
pps- SiO2's surface softens when exposed to water, plants count on
that property, I'm not convinced of the meat cutting properties
yet, but recently I've learned to knap so that's something me
and my buddies will have to try out on a cow
ppps-http://www.panix.com/~alvinj/oldest.htm
Hey Alvin, Cliff is being nice enough to let me borrow a 1095 at 66 RC
paring knife you made to cure my high carbide stainless steel blues.
I also need to get off my butt and start grinding the M2 hacksaw
blades Paul Hansen was nice enough to send me. While I must admit I
love my ultra thin ZDP 189 knives (.005" edge, high hollow ground,
very acute), the simpler steeled, much cheaper Byrd Meadowlark gets
sharper than those blades can get without chipping, at least with my
meager skills. I really look forward to trying some good ole tool
steel at high hardness to see what real sharpness and edge stability
is, in a steel that is ideally suited for the flat to the stone
sharpening I have come to love. Truthfully, I'm surprised how well
ZDP 189 does at very acute angles, I guess the hardness helps it to
overcome the extreme amount of carbides in it, and it does retain it's
edge for a very long time, though the very sharp initial edge fades
quickly to merely being sharp. The other great thing about the ultra
thin edges is even when I cut straight into the stone to dull it, it
will still outcut a lot of freshly sharpened factory knives on
cardboard. Ain't good geometry fun?
Mike
Mike