Quantitative measurement of sharpness
C Gollnick
blade sharpness that didn't produce satisfactory conclusions, IMHO. So,
I'd like to try it here and see if any of the collected experts can
provide some information.
Many knife enthusiasts are obsessed with sharpness. Many spend as much
on "magic sharpening gadgets" as the spend on knives. And they love to
brag and compare. They say: "This knife is sharp," "This knife is
reeeeealy sharp," "This knife is very, very sharp," "My knife is
shaving sharp," "Well, mine is 'hair popping' sharp," "Oh yeah, well
mine is 'scary sharp." (You can pick these people out in a crowd
because they have no hair on the back side of their left forearm.)
Maybe it's just my technical, scientist, engineer background, but I
don't like to measure things based on the hair on the back of my arm and
I don't like vague qualitative metrics like "really sharp", "shaving
sharp", and "scary sharp."
There must be some sort of precise quantitative metric for blade
sharpness. What is it? What is the SI unit of sharpness and how is it
measured?
For example, I've been involved in the past with military procurements.
They specify every detail right down to the color of the tape to be used
on the shipping box and then they inspect the product and verify your
compliance with every spec.
When the military buys a knife, I'm sure they don't say it has to be
"very long." No, I'm sure they say, "The overall length of the knife
measured as illustrated in figure 523 shall be 300mm +/- 3mm." And when
they get the finished goods, you can bet that they'll measure 'em.
I'm sure they don't say, "make it out of really good steel." No, I'm
sure they specify exactly what alloy to use. And when they get the
finished goods, you can bet that they send a few samples to the lab to
check.
I'm sure they don't say, "make it darn hard." No, they say, "The blade
shall be 59-61 HRC as defined in Mil. Spec. XYZ123." And you can bet
that they'll test samples too.
I'm sure that they even specify the color using either Federal Color
Numbers or Pantone numbers.
Precise, repeatable, quantitative measurements are important. What if
the Army says, "These blades aren't hard enough. We're rejecting them
and not going to pay." But, the supplier believes that the blades meet
spec. If the spec says, "really hard," or "scary hard", how are you
going to settle that argument? Remember, there could be a lot of money
on the line here. But, if the spec is quantitative, 59-61 HRC, then
samples can be tested by a independent, accredited lab using calibrated
equipment traceable to the NITS, and the answer will be known.
So, there has to be a standard, quantitative measure for sharpness.
Any answers?
Chuck
Kevin Malin
it. I think you have to come up with a test that suits you and use it.
"X pounds of force (oops, no SI) produces a push cut of 30 inches
through xyz cardboard" or something.
Think about it. When the army wanted a pistol with more stopping power,
you can calculate ballastics this way and that way. In the end, though,
they went out and shot goats and saw who died the fastest. This gave us
the .45 ACP.
The FBI could do all sorts of engineering calculations on pistol
cartridges, but when they wanted a 9mm replacement they also came up
with all sorts of emperical tests: ballastic geletin penetration, car
door penetration, windshield penetration and such. They didn't shoot
goats though -- that's not politically correct anymore.
Just my opinion.
Fred Whitlock
it needs sharpening again already. You could specify the
bevel angle, I suppose, but sharpness is something that's
applied to a knife, not built in-and, of course, it's quite
temporary.
Fred
Knife Outlet
http://www.knifeoutlet.com
Bernard R. Levine
testing machine, possibly inspired by the then fairly new Rockwell
hardness tester. The Honda machine used a stack of small strips of a
standard manufactured rice paper. The blade was held in a clamp and
sliced through the stack of paper diagonally, the resistance
encountered being a "measure" of sharpness. For measuring edge-holding
ability, the blade was sliced through the stack over and over, as the
stack was advanced by a screw-feed, until a pre-determined degree of
resistance was encountered -- the count being a "measure" of
edge-holding. Similar work was being done in Solingen at that time. I
am not aware of more recents attempts to quantify sharpness...
Aside from the fact that neither hardness nor sharpness is an
inherent property of any material, the basic uselessnes of this sort
of sharpness test should be fairly obvious. There were far too many
uncontrollable variables, and it was not at all clear what (if any)
useful qualities were REALLY being measured.
SEE:
Honda, Kotaro, and Kinnoske Takahashi, "On the the quantitative
measurement of the cutting power of cutlery;" Journal of the Iron and
Steel Institute, 1927, No. 2 pp. 356-384. As I recall, the article
includes photos of the apparatus. I'm pretty sure I have a copy
SOMEWHERE.....
For a brief history and description of Rockwell hardness testing, see
http://pweb.netcom.com/~brlevine/rockw.txt
BRL...
http://www.knife-expert.com/
C Gollnick wrote:
>
> There was recently a thread on bladeforums about the measurement of
> blade sharpness that didn't produce satisfactory conclusions...
C Gollnick
Thank you.
Chuck
"Bernard R. Levine" wrote:
>
> Back in the 1920s, a Japanese engineer named Honda, made a sharpness
> testing machine,
Duplete
edge and the width of the blade certain distances back from the edge.
Fred Whitlock <a...@cl-sys.com> wrote in message
news:800sp8$pim$2...@ffx2nh5.news.uu.net...
C Gollnick
They're have some validity because all of the guns in question were
fired by the same people who are experienced experts at about the same
time under about the same conditions, etc.
I'll bet that, today, though, the Army's Mil. Spec. for a .45ACP
cartridge it doesn't say anything about goats. I'll bet it's got a
bunch of numbers, a bunch of quantitative metrics.
You see, the spec forms the center of a contract between the Army and
Acme Ammo Co. (or whatever supplier wins the contract this time). It
can't be left to something as vague as goat stopping. When the Army
gets each lot of Acme product, they'll take samples into a lab and
conduct carefully prescribed tests that yield quantitative results. If
those results are not within acceptable bounds, they'll reject the lot.
If Acme believes that their product is within spec, then an independent
lab can be asked to test.
For a knife, they must have some testable, quantitative way to measure
the edge. The sharpness of the edge is just to important (one of the
most important aspects of a knife), to leave it unspecified.
Chuck
Blade
relative thing - a chisel has to be sharp in another way than, say, a
boning knife, which has to be sharp in another way than a razor.
I
f we define sharp purely as an edges ability to pass throgh a given
material of given dimensions while under a given pressure on the back of
the blade, and at the same time being moved lateraly a given distance
whilst under this aforementioned pressure, then we just might approach a
kind of standard meassure.
I am just not sure which material - blade geometry plays an awfully big
role when it comes to passing through various materials - and it would have
to be a stable, unchanging medium - a pineboard of a given dimension, or a
hemp rope of a given thickness would not do, since they would be all too
succeptible to changes in temperature, humidity etc. which would affect the
final result.
I am not sure that it can be done, but the question certainly is an
interesting one.
Blade
C Gollnick <goll...@spamcop.net> skrev i artiklen
<3823AF75...@spamcop.net>...
> There was recently a thread on bladeforums about the measurement of
Kallisti
><3823AF75...@spamcop.net>...
>> There was recently a thread on bladeforums about the measurement of
>> blade sharpness that didn't produce satisfactory conclusions, IMHO. So,
>> I'd like to try it here and see if any of the collected experts can
>> provide some information.
>>
>
Well, there's another one today (unless this is the one you were
referring to), which deals with Goniometers for measuring sharpness...
http://www.bladeforums.com/ubb/Forum32/HTML/000926.html
Kallisti
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