can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

wrote:

I want to * measure * knife sharpness. *In a repeatable, scientific
way. And preferably, non-destructive to the sharpened edge!

the floor is open for discussion.

I'm sure that there must be a methodology, and measuring equipment
available, the snag may be its cost and the time taken. If a blade does its
job, (the job for which it was designed), without any undue effort then its
probably sharp enough, if it will do so repeatedly without needing
re-sharpening at unreasonable intervals, then its probably right all
round,why would you want to know more? A razor that shaves without cutting
the skin or causing pain, is probably the right razor, if it does so at a
reasonable price in terms of either cost or maintenance, or both, then the
maker has got the edge right. The only reason I can think of for measurable
relative 'sharpness', is if one is entering into a 'sharpness' competition.
--
Nomen Nescio

wrote:

can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

You could measure the thickness of the cutting edge. Just about the
sharpest edge known is that of an obsidian tool. The edge is measured in
microns.

If you cut Anything, you have 'damaged' the edge.

wrote:

can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

You could perhaps measure the force it takes to cut a block of some soft
material, or the power it takes to do so in a given time interval.

S.

On Apr 12, 10:39 am, wrote:
can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!

the floor is open for discussion.

http://www.cutleryscience.com/articl...ss_review.html

-Cliff

http://www.cutleryscience.com/articl...ss_review.html
-Cliff

Aaa... there you are.
Where's Cliff when you really need 'im?
Johnny on the spot, that's where.

Alvin in AZ

If you cut Anything, you have 'damaged' the edge.

Oooo... that's where knife blades made from all-hard ~65hrc HSS
power hacksaw blades... come into the picture.

Maybe not the sharpest edge obtainable but will sure as heck get
sharp and cut a lot of stuff before you notice much difference.

http://www.panix.com/~alvinj/HSSknife.htm

Alvin in AZ

On 11 Apr 2007 22:39:25 -0700, wrote:

can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

How much money have you got?

I'm sure there are any number of ways, but they're all bound to cost a
lot.

Perhaps if you could find a second-hand optical comparitor and set the
knife on end to measure the blade width at the edge, that would work.
That would also be able to precisely measure the angle on either side
of the edge, and measure how closely it is to perfectly centered. But
the article another poster responded with raises a lot of good points-
sometimes those fine serrations *do* make for a better cutting tool.

"Prometheus" wrote in message
...
On 11 Apr 2007 22:39:25 -0700, wrote:

can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

How much money have you got?

I'm sure there are any number of ways, but they're all bound to cost a
lot.

Perhaps if you could find a second-hand optical comparitor and set the
knife on end to measure the blade width at the edge, that would work.
That would also be able to precisely measure the angle on either side
of the edge, and measure how closely it is to perfectly centered. But
the article another poster responded with raises a lot of good points-
sometimes those fine serrations *do* make for a better cutting tool.

The sharpness is not in the tool but in the cutting. When it comes to thin,
you also have to consider fragile, a phenomenally thin-edged metal object
for bar bets and workshop brags would certainly be called sharp, but remain
useless.

wrote in message ...
http://www.cutleryscience.com/articl...ss_review.html
-Cliff

Aaa... there you are.
Where's Cliff when you really need 'im?
Johnny on the spot, that's where.

Alvin in AZ

If that's Cliff, he's changed his email address.

wrote:
can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.


Zygo NewView white light interferometer or equivalent. Form Talysurf.
Scanning probe AFM. If simply interested in cutting ability you could
cobble up a hardness tester and cut into some standard material.

--
jeff

wrote:

If you cut Anything, you have 'damaged' the edge.

Oooo... that's where knife blades made from all-hard ~65hrc HSS
power hacksaw blades... come into the picture.

Maybe not the sharpest edge obtainable but will sure as heck get
sharp and cut a lot of stuff before you notice much difference.

With the right microscope, you can see the damage. )


http://www.panix.com/~alvinj/HSSknife.htm

Alvin in AZ

On Apr 12, 6:18 pm, "Lynn Coffelt" wrote:
I want to _measure_ knife sharpness. In a repeatable, scientific
way. And preferably, non-destructive to the sharpened edge!

Shop teacher 60 years ago taught measuring sharpness using a simple yet
scientific method. Look at the edge! Yup, just look at the edge, straight
on, under window light. If you can see the edge, it's not sharp.
Worked then and works now.

Beat _me_ to it, willya?

Exactly correct though, no fancy instrumentation needed; just a
decent light and the Mark I eyeball. I learned it a tad more recently
though; a mere 45 years ago. ;)

The OP will be interested to know that a very good optical (as in
laser) beam dump comprises a stack of brand new de-oiled single edge
razor blades bolted together with edges parallel. The edges do not
reflect and any light that falls between them bounces down into the
narrowing gaps and can't get back out.


Mark L. Fergerson

I want to _measure_ knife sharpness. In a repeatable, scientific
way. And preferably, non-destructive to the sharpened edge!

Shop teacher 60 years ago taught measuring sharpness using a simple yet
scientific method. Look at the edge! Yup, just look at the edge, straight
on, under window light. If you can see the edge, it's not sharp.
Worked then and works now.

Old Chief Lynn

[This could be me at my ANALytical best...]

In other parts of woodworking (e.g., hand planes) it is common to
evaluate the sharpness by how thin of a shaving you can get. The keener
the edge the less compression is required to press the blade into the
wood and get the wood to flow over the top of it, thus creating the
shaving. This is at a planing angle, not a chopping angle.

When I evaluated several of my turning tools for the kind of edge they
would take I did the following:
- Set up a block of soft maple in a faceplate type of turning
- Sharpen then hone each tool with an slipstone.
- Cut a profile into the faceplate that matched the shape of the gouge.
- Re-hone the tool
- Take the thinnest, softest cut I could from the pre-prepped area.
- Measure the thickness of several of the shavings.
- Clean the shavings off the lathe and start again with another tool.

I went through an assortment of bowl and spindle type gouges but I did
not try a skew.

The differences were not so much based on the manufacturer but more the
type of steel used. Here's what I came up with:
- Powdered metal gouges (Glaser, Crown Pro-PM) got shavings down to 0.002".
- 'Normal' HSS tools (Sorby and Crown) got shavings to 0.001"
- My sole Henry Taylor 'Kryo' required that I double up shavings to get
them to read over 0.001". My SWAG is they were about 0.0007" thick.

This is pretty much what theory says should happen. The tools with the
finer grain structure should achieve a keener edge.

I haven't tried an edge-holding test -- yet. I am curious how the Kryo
tool will hold up.

Does this help you out?

Anyone want to try to reproduce these results to see if they hold?

David O. Wade

wrote:
can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!


the floor is open for discussion.

On Apr 12, 1:39 am, wrote:
can you imagine if the conventional wisdom for judging size-tolerance
of fabricated-materials was along the lines of, "how does it feel when
i shave hairs on my arm?"

I want to _measure_ knife sharpness. In a repeatible, scientific
way. And preferably, non-destructive to the sharpened edge!

the floor is open for discussion.


the problem with SHARPNESS is it is not a good measure of the
effectiveness of a cutting tool. so even quantifiabbly measuring
sharpmess means nothing in itself. Sharpness will be like Watts in car
stereos or Horsepower in motors and compressors

The reason i say that is that the Cutting tool is dependent on the
material being cut for its effectiveness.
by knife standards a SAW is a thick flat edge with 0 sharpness but its
very effective at cutting trees.


If i use trees as an example try cutting a tree down with a splitting
maul and you will be into one of the most frustrating experiences of
your life. Just a little less so than splitting wood with a felling
axe

the felling axe is sharp and is made for cutting the splitting axe is
meant for prying wood apart sharpness is not very useful to a
splitting maul since it is serving as a LEVER not a blade

Food

Sharpness is a DETRIMENT to effectively slicing soft or airy foods.
Take a loaf of bread, a tomato, and an appleas examples

a Bread knife has a serrated edge and cuts with a sawing type motion
because Bread is mostly air with fibres of bread itself tham move
easily, its impossible to no have then crush someonwhat under an
unfirm blade so a sharp sawing motion catches it

A tomato is similar loose fibers in mostly water a knife with some
roughness on the edge slices it BETTER that a purely sharp edge to
avoid

an apple is MUCH more firmly put together and a purely sharp edge cuts
it better than the earlier two


There are as many different ways to sharpen a blade as there are ways
to prepare lathe toolbits.

EVERY material does better with certain angles or feed types or feed
speeds

Sharp isnt everything but SOMETIMES sharpest is best other times it
isnt

But dont confuse a worn edge with an edge that is not sharp.

I keep my pocket knife edge very fresh but at an angle to deal with
anything i might come across (I dont measure it but it is likely about
a 30 degree angle based on how i hold my hand while sharpening. It
needs to still be in decent shape if i need to cut copper wires or
strip coating or chop off plastic tiewraps i wont be using it for fine
detailed cutting. But a filleting knife i would have sharpened to a
FAR steeper angle for a far finer cut and so that it might wear down
FAR faster if it was cutting anything firmer than a fish

I can chop through copper cable with my pocketknife if i need to and
then need to resharpen it at the end of the day. my kitchen knifes or
chisels would have their edge ruined doing that immediately.

Sorry for the long Post but the overall point of it is Sharpness is
not a direct measure of effectiveness

Brent

Ottawa Canada

If you cut Anything, you have 'damaged' the edge.
Oooo... that's where knife blades made from all-hard ~65hrc HSS
power hacksaw blades... come into the picture.
Maybe not the sharpest edge obtainable but will sure as heck get
sharp and cut a lot of stuff before you notice much difference.
http://www.panix.com/~alvinj/HSSknife.htm

With the right microscope, you can see the damage. )

Agreed.

Maybe even just one of those "stamp collector" lighted 30x things
from Radio shack after enough cuttin?

A guy can skin-out a whole cow with one of those knives made
from 65hrc M2 HSS and not have to stop to sharpen.

Like comparing carbon steel hand hacksaw blade with HSS or bi-metal
ones. Anyone that's -been there and done- that will recognize the
edge holding potential of a knife made from an all-hard power
hacksaw blade, right away. Industry claims a 5 to 7 times
difference.

"...but there's more!"

Factory made knives aren't 65hrc like the "sorry ass" carbon steel
hand hacksaw blade's teeth are, neither...

Like Brent said (and went on and on about there's more to this
than just sharpness.

Alvin in AZ

"Lynn Coffelt" wrote:
Shop teacher 60 years ago taught measuring sharpness using a
simple yet scientific method. Look at the edge! Yup, just look
at the edge, straight on, under window light. If you can see the
edge, it's not sharp.
Worked then and works now.

Beat _me_ to it, willya?
Exactly correct though, no fancy instrumentation needed; just a
decent light and the Mark I eyeball. I learned it a tad more
recently though; a mere 45 years ago. ;)

Yeah but you got 'im beat in that your's is newer, more up to date
information.

The OP will be interested to know that a very good optical (as in
laser) beam dump comprises a stack of brand new de-oiled single
edge razor blades bolted together with edges parallel. The edges
do not reflect and any light that falls between them bounces down
into the narrowing gaps and can't get back out.
Mark L. Fergerson

Don't know nuthin about the OP :/ but this dumb knife knut found
that really cool.

Alvin in AZ

In rec.knives Dave Lyon wrote:
http://www.cutleryscience.com/articl...ss_review.html
-Cliff
If that's Cliff, he's changed his email address.

Yeah, the school freaked out over the volume his knife stuff was
getting.

Alvin in AZ

In article .com, " writes:
On Apr 12, 6:18 pm, "Lynn Coffelt" wrote:
I want to _measure_ knife sharpness. In a repeatable, scientific
way. And preferably, non-destructive to the sharpened edge!

Shop teacher 60 years ago taught measuring sharpness using a simple yet
scientific method. Look at the edge! Yup, just look at the edge, straight
on, under window light. If you can see the edge, it's not sharp.
Worked then and works now.

Beat _me_ to it, willya?

Exactly correct though, no fancy instrumentation needed; just a
decent light and the Mark I eyeball. I learned it a tad more recently
though; a mere 45 years ago. ;)

The OP will be interested to know that a very good optical (as in
laser) beam dump comprises a stack of brand new de-oiled single edge
razor blades bolted together with edges parallel. The edges do not
reflect and any light that falls between them bounces down into the
narrowing gaps and can't get back out.

Yes, an excellent black body approximation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

wrote:

A guy can skin-out a whole cow with one of those knives made
from 65hrc M2 HSS and not have to stop to sharpen.

I usually try for deer or elk. Cows are a last resort. :P

According to :

[ ... ]

The OP will be interested to know that a very good optical (as in
laser) beam dump comprises a stack of brand new de-oiled single edge
razor blades bolted together with edges parallel. The edges do not
reflect and any light that falls between them bounces down into the
narrowing gaps and can't get back out.

The question which I have is how do you get them clamped
together close enough? The single-edge have the folded piece of steel
along the back edge.

Double-edge don't have that extra thickness to deal with, and
probably those skinny injector blades would do as well.

Do they still make those injector blades? I haven't shaved
since about 1978 or so, and while I use single-edged blades for other
purposes, I haven't kept track of the competition in blades since I
shaved. (And when I did, I either used double-edged, or a Rolls Razor,
which was a short length of blade from something like a folding
cutthroat razor mounted in a case which would hone and strop it for you
prior to your mounting it in the handle.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"Brent" wrote:

A tomato is similar loose fibers in mostly water a knife with some
roughness on the edge slices it BETTER that a purely sharp edge to
avoid

.... and we'll also throw in the Offset Cleaver! )

On Apr 11, 10:39 pm, wrote:

If you want to measure some sort of penetration, you could try using
machinable wax as a test material. It's supposed to be reusable and
nondestructive to cutting tools.

On Apr 12, 10:26 pm, (DoN. Nichols) wrote:
According to :

[ ... ]

The OP will be interested to know that a very good optical (as in
laser) beam dump comprises a stack of brand new de-oiled single edge
razor blades bolted together with edges parallel. The edges do not
reflect and any light that falls between them bounces down into the
narrowing gaps and can't get back out.

The question which I have is how do you get them clamped
together close enough? The single-edge have the folded piece of steel
along the back edge.

You can order unbacked blades in bulk from the mfgrs (if you're
building beam dumps you want a bunch anyway).

And yes, some like to use double edged blades and rotate the stack
if some idio^H^H^Hundergrad dings the working face.

Double-edge don't have that extra thickness to deal with, and
probably those skinny injector blades would do as well.

Sure, but they're harder to align and clamp.

Do they still make those injector blades? I haven't shaved
since about 1978 or so, and while I use single-edged blades for other
purposes, I haven't kept track of the competition in blades since I
shaved. (And when I did, I either used double-edged, or a Rolls Razor,
which was a short length of blade from something like a folding
cutthroat razor mounted in a case which would hone and strop it for you
prior to your mounting it in the handle.

Yeah, they still make injector blades for shaving geeks who buy
ancient razors on E-bay these days. I still use a "Square Deal" brand
straight razor I got at an estate sale. I used to use el cheapo Bics/
Crickets/etc. but eventually the engineer in me demanded I do
better. ;)


Mark L. Fergerson

On Apr 13, 7:41 am, wrote:
In rec.knives Dave Lyon wrote:

http://www.cutleryscience.com/articl...ss_review.html
-Cliff
If that's Cliff, he's changed his email address.

Yeah, the school freaked out over the volume his knife stuff was
getting.

Yeah, it got more traffic than everything else combined so I had to go
external for hosting. My email is still working,
that they can handle. But I had to remove all the webpages.

-Cliff

On Apr 13, 6:57 am, "Brent" wrote:

the problem with SHARPNESS is it is not a good measure of the
effectiveness of a cutting tool.

That I would argue is a poor defination of sharpness. I defined it in
the article linked to in the above.

-Cliff

Injectors ancient? Not compared to the 1904 Gillette I use.

" wrote in message
ups.com...
Yeah, they still make injector blades for shaving geeks who buy
ancient razors on E-bay these days. I still use a "Square Deal" brand
straight razor I got at an estate sale. I used to use el cheapo Bics/
Crickets/etc. but eventually the engineer in me demanded I do
better. ;)

On Apr 13, 5:02 pm, "CW" wrote:
Injectors ancient? Not compared to the 1904 Gillette I use.

" wrote in message

ups.com...

Yeah, well, such things are relative. I still have no clue how old
the Square Deal I have is.


Mark L. Fergerson

In rec.knives DoN. Nichols wrote:
I haven't shaved since about 1978 or so... a Rolls Razor, which
was a short length of blade from something like a folding
cutthroat razor mounted in a case which would hone and strop it
for you prior to your mounting it in the handle.
DoN.

I've got one of those things.
No wonder you quit shaving. :/

Alvin in AZ

In rec.knives Lobby Dosser wrote:
A guy can skin-out a whole cow with one of those knives made
from 65hrc M2 HSS and not have to stop to sharpen.

I usually try for deer or elk. Cows are a last resort. :P

Yeah "slow elk" is what some "hunters" call 'em.

Deer skinning is more like really-big-rabbit skinning and ain't
much of a test for a knife. But elk now, that is.

Alvin in AZ

In rec.knives woodworker88 wrote:
If you want to measure some sort of penetration, you could try
using machinable wax as a test material. It's supposed to be
reusable and nondestructive to cutting tools.

But like Brent's "tangent" is that about cutting ability or is
about edge sharpness?

My test is to feel-for and look-for hairs being cut when raking the
edge of the blade through the hair (peach fuzz) on my arm... in
mid-hair. Try that with a brand new razor blade that's been removed
from the holder. It'll cut-off dammed-near ever hair it contacts
and leave them laying on the blade.

My HSS skinning knife will leave quite a few hairs laying on the
blade. It's easy to get it to do that at a 5 degree honing angle
when the steel is as strong as 65hrc.

Try it.

Try the mid-hair (mid-air? test with a new razor blade, so you'll
know how sharp a piece of steel can get. Cheap.

Alvin in AZ

wrote:

Yeah "slow elk" is what some "hunters" call 'em.

Deer skinning is more like really-big-rabbit skinning and ain't
much of a test for a knife. But elk now, that is.

Alvin in AZ


Maybe not much of a test for the knife; but it's real hard on the deer. ;-)


--
http://nmwoodworks.com/cube


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wrote:

Try the mid-hair (mid-air? test with a new razor blade, so you'll
know how sharp a piece of steel can get. Cheap.

Somebody must have tried it: drop a hair on the blade edge.

On Apr 13, 6:49 pm, wrote:
In rec.knives woodworker88 wrote:

If you want to measure some sort of penetration, you could try
using machinable wax as a test material. It's supposed to be
reusable and nondestructive to cutting tools.

But like Brent's "tangent" is that about cutting ability or is
about edge sharpness?

Alvin in AZ

Yep. I see what you mean.

On Apr 13, 6:11 am, "Cliff" wrote:
On Apr 13, 6:57 am, "Brent" wrote:

the problem with SHARPNESS is it is not a good measure of the
effectiveness of a cutting tool.

That I would argue is a poor defination of sharpness. I defined it in
the article linked to in the above.

-Cliff

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

"Lynn Coffelt" wrote in message
...

I want to _measure_ knife sharpness. In a repeatable, scientific
way. And preferably, non-destructive to the sharpened edge!

Shop teacher 60 years ago taught measuring sharpness using a simple
yet
scientific method. Look at the edge! Yup, just look at the edge, straight
on, under window light. If you can see the edge, it's not sharp.
Worked then and works now.

interesting... verry interesting...

no wonder grandma's knives seem dull - grandpa has bad eyes...

reminds me of the long-time several-page-standard for measuring the
transparency of fluids: with its multi-part equations, tight protocol, the
part about "when transparency falls below 10 mm (?), mix ten parts
non-reacting clear fluid to one part test material, and divide results by
ten." -- several quite specific steps - and then near the last step of the
protocol -

- record the depth of subject fluid (in the "X" ml beaker) at which you can
read black "y" pt courier type printed on white paper.


Old Chief Lynn

wrote in message ...
If you cut Anything, you have 'damaged' the edge.
Oooo... that's where knife blades made from all-hard ~65hrc HSS
power hacksaw blades... come into the picture.
Maybe not the sharpest edge obtainable but will sure as heck get
sharp and cut a lot of stuff before you notice much difference.
http://www.panix.com/~alvinj/HSSknife.htm

With the right microscope, you can see the damage. )

Agreed.

Maybe even just one of those "stamp collector" lighted 30x things
from Radio shack after enough cuttin?

A guy can skin-out a whole cow with one of those knives made
from 65hrc M2 HSS and not have to stop to sharpen.

That would not be a test of sharpness to me - that seems more like a test of
toughness and wear.

A test of sharpness would be more like "skinning out" a shrew or a
hummingbird eyelid.

You might check a plastic surgery tool manufacturer to see what standards
they use - they have QC standards for the sharpness level needed to remove
one layer of cells.

FWIW - apparently it's less work to skin a cow with a prehistoric flint
knife than with a modern steel one (for good technical reasons btw) - and
knives are going back to that early shape - instead of the one dimensional
action of classic metal blades, using the two-dimensional flaring- edges to
put parting tension on the materal for the cutting edge (scalloped edges),
ceramics which approximate flint's hardness instead of the softer hardened
metal, etc.


Like comparing carbon steel hand hacksaw blade with HSS or bi-metal
ones.

Again, the latter are made for toughness and heat-strength, not "edge
sharpness" per se.

Anyone that's -been there and done- that will recognize the
edge holding potential of a knife made from an all-hard power
hacksaw blade, right away. Industry claims a 5 to 7 times
difference.

"...but there's more!"

Factory made knives aren't 65hrc like the "sorry ass" carbon steel
hand hacksaw blade's teeth are, neither...

Like Brent said (and went on and on about there's more to this
than just sharpness.

Alvin in AZ

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

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