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Knife Grinders -- What Edge Angle Is Good For SuperSteels

Posted by jasonstone20 
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Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 28, 2020 09:05PM
Could someone point me to experimental data or tests that contradict our findings? - that a knife of tool steel or supersteel holds well an edge under 10 degrees per side?
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 02:28AM
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KnifeGrinders
Could someone point me to experimental data or tests that contradict our findings? - that a knife of tool steel or supersteel holds well an edge under 10 degrees per side?

Supersteel isn't a grade of steel, steels are materials, super is a marketing term, steels are materials with well known properties which make each steel suitable for various uses and not useful for others. There are steels which have very expensive processing requirements, but it no more makes them a super steel than the same thing effectively makes Kim Kardashian a super woman.

I am not sure how you could contradict that claim as it isn't quantified, it would be like if someone said :

-can you contradict my claim that someone can not run fast while carrying a weight

What is "run fast", and how are they carrying and how much weight, and is it a track, up a hill, etc.?

In regards to holding a high polished edge, high sharpness, Landes work shows the negative correlation to higher carbide volume, and it maximizes with AEB-L and similar steels as they can achieve full martensite hardness ~65/66 HRC and have a well dispersed array of sub-micron carbides.

I have edge retention work ~20 years old, showing knives with edges ~5 dps, which cut materials like ropes, cardboard, woods, foods, etc. and the edge retention simply increases as you drop the angle down to 5 dps. 5 dps wasn't the point I stopped because it failed there, I just could not sharpen any lower with that particular knife (it was convex ground and that was sharpening it flat on the abrasive).

I have also quantified this increase in edge retention as a function of angle in the past. Larrin has done the same more recently. Buck did it with CATRA in the 2000's, however care has to be taken as CATRA and similar work isn't really showing an increase in edge retention in that kind of comparison as they are confounding edge retention with force required to cut something (a fillet knife will cut rope longer than an axe even if blunt because the axe will fail due to requiring too much force even when it is sharper, CATRA doesn't separate these two measurements).

As a point of history, full size chopping axes have apex bevels of ~15 dps, and that is a 3 lbs head swung by a man slamming into a piece of wood, so even without any data, it would not be surprising that a knife made out of a much stronger steel, which is subjected to far lower forces, should be able to sustain them without damage and hence blunt by slow wear (for which lower angles -> higher edge retention).

In general, very general :

-knives blunt by wear, deformation, fracture and corrosion resistance
-corrosion resistance isn't sensitive to angle
-the goal to maximize edge retention is to minimize the angle which prevent deformation (and to a lesser extend fracture)

As to what is the minimal angle, well it depend on :

-what is being cut
-skill
-force

A skilled user, low force, cutting soft targets can use a much lower angle than the opposite.

(the reason why it is to a lesser extent fracture as edges rarely fail by toughness related issues, because the rate of strain application is always very slow compared to the ability of a steel to deform plastically in cutting, assuming you are not cutting hard targets like rock, metal etc. and if you are, well edge retention isn't a concern anyway)
me2
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 03:26AM
I had no issues using a Parker Cutlery knife several years ago to cut aluminum. It was an unknown stainless sharpened at 7 dps. Cut several feet of sheet aluminum and would still whittle beard hair. Brought the edge back down to 12 dps because the bevel was so wide sharpening took forever.
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 08:20AM
No one argues here that thin edges cut better.

Cliff, I think I remember seeing that 20-year old chart you mention. It was an excellent study, but your edges all have 20 dps microbevel.
Me2 - your knife of 7 dps had microbevel of 15-20 dps, hadn't it?

I doubt there are any test data that a knife edge under 10 dps is stable in cutting. Because by what I see, apex of common knife steels becomes unstable under 10 dps.



Edited 4 time(s). Last edit at 07/29/2020 08:44AM by KnifeGrinders.
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 01:44PM
Quote
KnifeGrinders
Cliff, I think I remember seeing that 20-year old chart you mention. It was an excellent study, but your edges all have 20 dps microbevel.

I rarely use a 20 dps apex bevel, in comparisons I use 15 dps, mainly because that is the angle preset on a Sharpmaker and I like to have that as a reference for a consistency check. Outside of comparisons, I don't go to 15 dps unless it is an axe, it simply is not needed for strength and any angle above the minimum stability point just reduces cutting ability, control, edge retention, etc. .

I have done work without apex bevels, it just isn't as efficient sharpening wise, as an example of a ~5 dps edge bevel :

[www.cliffstamp.com]

That isn't the limit, that was sharpened flat to the blade, it just picked up a hint of a curve which steepened the bevel to ~5 dps at the apex due to the convexity. That isn't the ideal steel for that experiment, or hardening anyway. Something like the FF D2 at close to 70 HRC would be able to be thinner in section due to the higher strength. The HSS with extreme alloy content would be higher still. However care has to be taken as the percent changes get very high, the a 2.5 dps bevel is 1/4 the strength of a 5 dps one for example even though they would look almost identical to the eye.

Note that when I say I run apex bevels, that is what they are, apex bevels. They are not visble, they are set with 1-2 passes on the stone, the wear on the knife is into the edge angle itself, so the knife is cutting with the edge angle for the majority of its lifetime. The apex bevel is for sharpening, not for durability reasons. It simply achieves no functional purpose to have the edge geometry at the finish of the apex, hence, apex bevel.

Quote

I doubt there are any test data that a knife edge under 10 dps is stable in cutting. Because by what I see, apex of common knife steels becomes unstable under 10 dps.

Again, a simple consideration of physics would show that could not be the case because :

-axes have 15 dps apex bevels, and their loads are much higher

It doesn't take an engineering degree to realize if an axe can slam into wood at 15 dps and not have the apex fail catastrophically, a knife cutting ropes, woods, foods etc. should be able to be much lower because it doesn't need the strength. The impact energies on the knife edge have to be 100 to 1000 times lower than the axe.

[www.cliffstamp.com]

That is a piece of unhardened mild steel at 12 dps, perfectly stable cutting ropes, woods, etc. .

Anyway, all of this aside, the main content with your claim isn't that some particular angle is required for some particular cutting. As this is going to be controlled by :

-skill
-experience
-material being cut

For a given knife it could be the case that productive angles range significantly. The main point of contention is the claim that higher carbide volume allowed finer edge angles, that directly opposed Landes work, and the general materials data he cites in the research he uses to support it. Larrin also talks about this, and other things in his work.

Now of course if you are not talking about high sharpness, and instead talking about cutting with low sharpness for a long time, then higher carbide steels will outperform lower carbide steels due to wear resistance, that isn't controversial. For cutting abrasive materials, where deformation and impact are not significant modes of blunting, edge retention will correlate well to CATRA which correlates well to MC carbide volume if it is present, otherwise to general carbide volume. The literature is full of empirical formula like that to predict wear based on composition.



Edited 1 time(s). Last edit at 07/29/2020 06:28PM by CliffStamp.
cKc
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 06:22PM
When talking about edge angles, and damage I think we also need to be clear on how big the edge angle is.

for example... when some people talk Micro bevels.. often for me, that is the edge..

as an example

one of my paring knives, as demonstrated in a video recently I did, but here is a quick picture


this blade is 14mm wide, 1mm thick..

a true zero grind would leave this at 2bps and very thin.

this knife as measured and checked with microscope to be fairly accurate is
reprofiled vicnox paring knife
Primary Bevel 2 dps
Edge
cross section on knife -> distance from apex, -> angle at that point.
0.010" -> 0.76 -> 3.7DPS
0.005" -> 0.032 - 4.5 DPS
APEX EDGE less than 0.001 from edge 6dps
Actual edge angle estimated from cutting into foam, 8dps

so.. if I was going to use the terminology most were using a 10dps edge to 0.010 which is I doubt any tormek sharpening is going this thin generally in the knives we are discussing. would be
0.010 -> 0.028" -> 10dps
0.005 -> 0.014 -> 10dps

which are significantly thicker.

even if I raised my edge to 12.5dps, it would only be 12.5dps for 0.001" cross section at most, which will fully stabilize this knife to cut wooden kebab sticks, as it is, it can take very minor damage than you can feel, but wont effect the knife use in general..

but the difference is even if I did that, its 12.5dps for a cross section of 0.001 and a little over 0.002" long, before we hit 4.5DPS or so.

this is massively different from talking about 12dps, or 10dps or 8dps to knife thicknesses common of 0.005, 0.010 - 0.020


so even if 12.5 was a magic threshold that is implied, then it only needs to be 12.5 dps to the height at which damage normally occurs, a few thousands, before hitting primary edge, at which point the performance is so much superior to a knife that is 12.5 dps that is hard to say without someone trying.

but when you get knives that are always < 7dps down to the final 0.001 of the edge.. then we are talking about useable knives.

now bear in mind this is a low hardness steel. as a knife maker this is not abnormal.


this knife I'm testing here scraping bamboo is around a 0.001" edge flat ground behind it, it is much thinner than this paring knife, and 61/62rc










you can see how thin it is from the flexing there, and this knife is more than durable as per the above test to work all day on hard work.

its more stable than the Victorinox, but I run my Victorinox knives thinner than most custom knife makers make their high hardness steels..

my AEBL kitchen knives will easily support 10dps at 0.002" for normal kitchen work and chicken bones.

the Victorinox boning knife by the way is 10.5dps and 0.010" thick on the thickest part of the edge and I've been using it light duty dismantling a couple of chickens a week for a few months now with no edge degradation..

so I think I can calmly say after using and making knives this thin for a while now, that yes.. knives can easily support this. but of course that doesn't mean unskilled users wont damage them.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 06:37PM
Quote
cKc

so I think I can calmly say after using and making knives this thin for a while now, that yes.. knives can easily support this. but of course that doesn't mean unskilled users wont damage them.

It simply can't be the case you can say something like :

-X is an angle tolerance for knives

That is like saying X is a weight limit people can lift.

Which people? How are they lifting it? For how much?

-what is the knife being used for
-how skilled is the user
-how much force/speed is being applied
-how is the steel hardened/hardness

These factors in order of importance can change the loads on a knife by a factor of a 1000 easily, which means they make the demands on the cross section of the knife by a factor of 10 roughly (stiffness is cubic and that will usually be your failure point). Hence this means knife angles should be expected to range by a factor of 10 across those ranges which seem sensible as it means angles would be expected to range from 3 to 5 to 30 to 50 dps, give or take.

I don't know what the limit is for low angles in skilled users on soft materials, based on what I have seen with a few, it is under 5 dps, but it also takes extreme geometries to allow that, going under 5 dps you need full hollow grinds because you have to sharpen almost flat. The only one really doing that was Alvin back in the 90's who sharpened < 10 dps, but his steels were also all high edge stability steels :

-1095 at 66/67 HRC
-M2 at 65/66 HRC

etc. . The blades were < 0.010" at 1/4" back from the apex, full hollow grind, sharpened flat to the stone and then slightly elevated. I measured some of them and they were in the 6-8 dps range, high polish, black arkansas mainly.
cKc
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 06:38PM


Another example. A large amount of.mass only 12.5 dps. Hard to imagine I need that kind of apex for kitchen work when this is house demolition

That knife is also 54rc

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
cKc
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 29, 2020 06:41PM
Quote
cliffstamp

It simply can't be the case you can say something like :

-X is an angle tolerance for knives

That is like saying X is a weight limit people can lift.

Which people? How are they lifting it? For how much?

Yes. What is being done by who will always be a bigger factor
For me. Thin is good. And if the knife is really thin then a slightly higher apex is ok. 10-12 typically is good for me on any steel for what I do for that last tiny apex

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 01:18AM
Quote
cKc
... A large amount of.mass only 12.5 dps. Hard to imagine I need that kind of apex for kitchen work when this is house demolition

That knife is also 54rc

The curious thing is sharpening angles for knives seem to have doubled in the current generation, if you look at manuals from the previous generation, they are really close to half. As stupid as it sounds, I think what happened is people were quoting included angles and they switched to per side and didn't change.

If you read Leonard Lee's book on sharpening, he notes a fillet or skinning knife can be sharpened at 15 degrees, he is talking about the INCLUDED angle (that is 7.5 degrees per side), even rougher knives are only 25 degrees included, and by the time he gets up to 30 degrees included, the knives are not really for cutting any more, more general purpose tools.

You could almost exactly write that now for dps and people would think it is reasonable.

I have no proof that happened of course, it is just kind of amusing to think.

In the 90's Alvin was trying to convince everyone the angles were way too high, Mike Swaim did some experiments, then Joe and Steve and noticed the huge difference if you change from 20 to 15 dps, and especially if you left the edges more coarse, the increase in cutting ability and edge retention was far greater than any steel could make.

I kind of took that to an extreme and noted that IF you took a piece of mild steel, and you ground it to cut as well as it could, and sharpened it properly, it would outcut and out last any of the dupersteel knives with the thick edge bevels with the 20-30 dps edges, and showed that this was the case with a number of experiments people could do.

Not the most popular stance, as my argument was knowing how to sharpen was far more important than the steel in your knife. But my parents/grandparents were fisherman/farmers and they knew it wasn't how expensive the equipment, it was the skill of the man using it.Put a $500 hammer in the hand of someone who can't swing it, and it does little obviously.
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 02:18AM
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CliffStamp
I kind of took that to an extreme and noted that IF you took a piece of mild steel, and you ground it to cut as well as it could, and sharpened it properly, it would outcut and out last any of the dupersteel knives with the thick edge bevels with the 20-30 dps edges, and showed that this was the case with a number of experiments people could do.

So in the case of my Fallkniven, there’s really not any need to go above 15 DPS unless I’m doing something relatively crazy like scraping paint off an old metal fence. Yes?
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 12:20PM
Above 15 dps you are heavier than a felling axe, so whatever you are doing it either isn't knife work, or the knife isn't made from steel.

Yes, for scraping and such there are extreme lateral forces, but again, as Kyley has noted, only the part of the knife which is subject to fail has to be the higher angle.
cKc
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 04:00PM
Quote
CliffStamp

The curious thing is sharpening angles for knives seem to have doubled in the current generation, if you look at manuals from the previous generation, they are really close to half. As stupid as it sounds, I think what happened is people were quoting included angles and they switched to per side and didn't change.

If you read Leonard Lee's book on sharpening, he notes a fillet or skinning knife can be sharpened at 15 degrees, he is talking about the INCLUDED angle (that is 7.5 degrees per side), even rougher knives are only 25 degrees included, and by the time he gets up to 30 degrees included, the knives are not really for cutting any more, more general purpose tools.

You could almost exactly write that now for dps and people would think it is reasonable.

I have no proof that happened of course, it is just kind of amusing to think.

I'm certain that this is probably what happened....
the only other alternative is that its purely because of silly warranties stuff that didn't used to exist to the same extreme competitive level
.
as time passes, we have people less skilled with knives and their maintenance, along with higher priced stuff available.

its not like in the old days everyone knew how to sharpen. there have always been service knife sharpeners, but it think certainly knives used to be thinner and more to purpose.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 04:32PM
Then I’ll have to re-do the sharpening on it and cut it back to 15 DPS I suppose.
cKc
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
July 30, 2020 08:54PM


one thing in all these conversations that is important to consider is that its not just about the apex angle, but also for how long it maintains that angle, and then what the angle is afterwards..

ie total cross section..

these 2 knives are both 11dps... the difference is that one is 11dps for 7.6mm and 3mm wide, and the other is 11dps for about 0.0762mm, only 100th the size.. after that its about 3dps..
so from a durability point of view, clearly there is no relationship between these 2 knives except for actual apex stability.. they both have the same apex stability (if they are the same knife) but one is much thicker, much more support.. once the apex is out of the picture, one will flex more, and have more compression on hard cuts causing warping of the apex under load etc etc..

why this is important is that for example.. if I have zero ground the paring knife its going to be 2dps, then I add a 0.001" 15dps apex, this is going to stabilize it a lot, but in cutting thin wood dowels without support, its still effectively a dps knife that the dowel can ripple the edge on, compared to a knife that is a 15dps wedge for 1/4" long..

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
August 02, 2020 08:14PM
In summary:
One can have a fairly robust edge at an angle of say 5-8 degrees per side, provided that you microbevel it at 15-20 dps.
However, with flat grind all the way to the edge apex you cannot go below 10 degrees per side as the apex will not cut without folding. We see it in our experiments, and cut throat razor owners know very well that the edge of a straight razor at 8 dps is destroyed by cutting even print paper.
Re: Knife Grinders -- What Edge Angle Is Good For SuperSteels
August 03, 2020 05:18PM
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KnifeGrinders

... cut throat razor owners know very well that the edge of a straight razor at 8 dps is destroyed by cutting even print paper.

This is likely caused by the way they sharpen, which plastically deforms the edge.

There is a wealth of data on knives which shows the same kind of sharpening, massive amounts of edge trailing passes, will produce very weakened edges due to plastic deformation, Verhoeven, Juranich, etc. spoke about that decades ago (JJ was first, I read it from him in the 90's, he had published it earlier).

Here is some simple physics which shows the above can not be true, lets assume it is in fact true that at 8 dps you can not cut paper because the apex does not have the required strength.

Now ask yourself, what is the relative impact energy on a blade which chops wood vs cutting paper. Lets be conservative and say it is 100X as much (it is actually much higher).

This means, if your assertion was true that a knife chopping wood had an apex angle of less than 80 dps per side it would also fail in the same way. It should be obvious this is incorrect.

As with anyone :

-defend the claims with data
-if methods are questioned due to lack of scientific rigor, then defend them

If your view is that claims don't require data, and/or data doesn't require scientific methods in collection/analysis in order to support conclusions, well there are likely other places which are more suitable, because that point all that is being done is spreading anecdotes, rumors and misinformation.

It isn't my goal or desire to police the internet, people are free to wander in any fantasy land they want, BUT here, science is respected, claims have to be evidenced, and arguments can't be dismissed without consideration. They are simple rules, but no one is exempt from them.