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Posting Flurry Thread 1: Convex Edges

Posted by me2 
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me2
Posting Flurry Thread 1: Convex Edges
October 01, 2012 03:30AM
I think I've about had all the convex edge hype I can stand. I can see no reason why putting a small arc to the edge bevel on a knife would improve/degrade it's cutting ability. I've used both convex and straight V bevels for years, alternating between my belt sander and my hand stones. I've noticed no difference, and in fact have seen the V bevels be more durable than the convex for roughly the same angles, though this is likely not due to shape, but sharpening method and steel choice. Many people convex their edges, and report better cutting. IMO, they are seeing better cutting because in the process, they thinned the edge and/or lowered the angle while changing the shape.

This notion that hand sharpening produces a slightly convex edge is, IMO, nonsense trying to capitalize on the latest cutlery buzz word, "convex". Yes it's true I suppose, but if you're accidentally convexing your edge, it's difficult to try to claim some benefit from it. At the very cutting edge apex, they're all straight bevels. With such relatively large radii, and very small arc lengths, I don't see it mattering. There is in fact something called the small angle approximation used in math and engineering. It says that for small angles of relatively large radius circles, the arc length and straight line length are effectively the same. Yes I know it's there and measurable, but if one want's to claim an advantage by the "natural convexing" of hand sharpening, then I'm going to claim there isn't any based on very small lengths of arc being effectively the same as straight lines.

This does not apply to the blending of the primary edge into the secondary edge on a knife. I see this as the true advantage of a convex edge/grind. Take an ESEE Junglas, sharpen the edge at say 15 dps, then lay the primary grind flat on leather backed sandpaper and blend the primary fully into the secondary edge, eliminating the shoulder entirely, and I'll say that will provide a noticable advantage. I'll also say that requires considerable skill and a lot of time and most people can't or won't do it because the advantage, while noticable, would not be worth the time. The exception would be something like a 0.015" - 0.020" edge bevel less than 1/16" wide. This might make the time spent worth it. One could always use power equipment, but that requires even more skill, though the time is cut considerably.
Re: Posting Flurry Thread 1: Convex Edges
October 01, 2012 11:18AM
Convex edge hype its out of control if you ask me but, not as much V edges with a bevel on it. And that its more tough nonsense to understand.

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A man is never too weak or too wounded to fight if the cause is greater than his own life.

---Doctore Oenomaus, in Spartacus---
Re: Posting Flurry Thread 1: Convex Edges
October 01, 2012 09:03PM
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me2

This does not apply to the blending of the primary edge into the secondary edge on a knife. I see this as the true advantage of a convex edge/grind. Take an ESEE Junglas, sharpen the edge at say 15 dps, then lay the primary grind flat on leather backed sandpaper and blend the primary fully into the secondary edge, eliminating the shoulder entirely, and I'll say that will provide a noticable advantage.


Yes but all you are doing here is simply reducing the thickness of the edge, the 15 dps part. Why not simply take the primary down to the optimal thickness in the first place, i.e., Boye, Wilson, Johnston, etc. .
Re: Posting Flurry Thread 1: Convex Edges
October 02, 2012 04:22AM
I'm a fan of the me2 posting flurries thumbs upthumbs upthumbs up
Re: Posting Flurry Thread 1: Convex Edges
October 02, 2012 09:23AM
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Chum
I'm a fan of the me2 posting flurries thumbs upthumbs upthumbs up

me too. he should start a blog or get his own corner with those things. can you imagine a radio show like that?
me2
Re: Posting Flurry Thread 1: Convex Edges
October 02, 2012 10:11AM
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CliffStamp
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me2

This does not apply to the blending of the primary edge into the secondary edge on a knife. I see this as the true advantage of a convex edge/grind. Take an ESEE Junglas, sharpen the edge at say 15 dps, then lay the primary grind flat on leather backed sandpaper and blend the primary fully into the secondary edge, eliminating the shoulder entirely, and I'll say that will provide a noticable advantage.


Yes but all you are doing here is simply reducing the thickness of the edge, the 15 dps part. Why not simply take the primary down to the optimal thickness in the first place, i.e., Boye, Wilson, Johnston, etc. .

For smaller knives like they make, that's exactly the reason I dislike all the "convex it" mess. For something like the Junglas, I'm not sure. Given the edge I have on my Barong, it should work there too. I need to find it and see how it might work.
me2
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:07AM
Ok, so out of curiosity, has anyone taken a knife and made some cuts on a scale, then convexed the knife (while keeping the same edge angle) and made some more to see how much difference it makes?
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:18AM
If you keep the same edge angle what exactly are you doing while convexing?
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:19AM
How do you convex the edge and keep the same edge angle? Don't you lose some steel when you convex the edge thus reducing the edge angle, even if it is only a slight decrease?
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:21AM
Hah! I was posting my question on my phone and you beat me to it Cliff.
me2
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:30AM
Not according to cKc's video. It's just knocking off the shoulder/corner where the primary and secondary bevels meet. I think it's just thinning the edge. The fact that they're curved doesn't matter. It's the same effect as a relief bevel.
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 02:36AM
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me2
Not according to cKc's video. It's just knocking off the shoulder/corner where the primary and secondary bevels meet. I think it's just thinning the edge. The fact that they're curved doesn't matter. It's the same effect as a relief bevel.

While Kylie does seem to know his stuff I don't agree with him on his edge convex video. If he is taking metal off of the knife he is reducing the cross section somewhere. Part of the knife may have the same angle as it did before it was convexed, but part of the knife is thinner... which should lead to increased cutting performance... which in fact it does.
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 01:15PM
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CliffStamp
If you keep the same edge angle what exactly are you doing while convexing?

Exactly why I don't get into these topics anymore.
Re: Posting Flurry Thread 1: Convex Edges
November 02, 2012 08:13PM
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me2
It's just knocking off the shoulder/corner where the primary and secondary bevels meet.

That is just lowering the angle in that area creating a transition bevel. Now some people argue that removing the sharp shoulder itself, just rounding it over creates a huge response, physically that isn't possible. The bulk of the cutting ability will come from the thickness of the cross section. The real problem in the level of vagueness in the descriptions, simply saying "I convexed the edge" doesn't give enough information to be meaningful. Just imagine someone telling you they v-edged a convex knife, could you infer if the performance would be improved or not? A pair of calipers would solve all of these problems.

I have reground knives and noted the difference in performance (rope, wood, chopping, etc.) but it was always with a specific description of the angles/thickness of the material before and after.
cKc
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 03:23AM
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me2
Not according to cKc's video. It's just knocking off the shoulder/corner where the primary and secondary bevels meet. I think it's just thinning the edge. The fact that they're curved doesn't matter. It's the same effect as a relief bevel.

Yes, Its just thinning the steel Behind the edge allowing for an easier transition.

Cliff.. Rounding the shoulder (literally) probably wont have much effect unless steel is removed except for the arguable fact that in polishing the shoulder it will reduce friction somewhat and perhaps have a little less drag when the shoulder is trying to interrupt cutting.. In reality, i suspect it has more to do with the act of thinning and polishing.

Chum, Not sure which specific video you are referring to of mine.. but when talking about edge angle and convex knives I am only ever talking about the angle at the apex of the knife. this angle might only be sustained for 0.00001mm for example as a convex in nature is a continually lessening angle. When I say that a convex knife of 12 degrees will cut better than a flatground knife of 12 degrees, I'm typically referring to a knife with a secondary bevel of 12 degrees where the lessening nature of the convex means there is less steel behind the edge itself.

As to the adding of a flat microbevel onto a convex knife.. I do it very often.. is my micro bevel flat or curved? too small for me to care. I add them where my apex on the knife is just lesser angle and thinner than I want and I dont want to increase the thickness of the knife to excess by having a zero ground convex of fuller body throughout.


"How do you convex the edge and keep the same edge angle? Don't you lose some steel when you convex the edge thus reducing the edge angle, even if it is only a slight decrease? "

You can convex an edge and maintain the exact same Apex edge angle, which reducing the cross section of everything behind it. This is more useful in converting a secondary bevel. on a full flat zero edge it would require thinning of the knife spine to acheive.

At the end of the day. I think the answer is fairly simple. Thinner knives cut better, no matter how the thinning is acheived. Most importantly, thinning the cross section at the cutting edge makes them cut better. there is no point taking a 5mm knife to 3mm at the spine of the cross section is equally thick behind the cutting edge. You might reduce weight, and reduce follow through resistance, but it wont increase the cutting performance.

I personally advocate Convex because I prefer them. I belive the are better in general terms. I feel in all my testings that the cut more fluidly. If all you are doing is a hair splitting test, then none of this is relevant.. what you cut will always dictate how much you notice the difference.

I can, for example, notice the difference in cutting between a full convex chef knife in cutting potatoe, and a flat ground one.. many people might not easily visually identify the difference, but simply using it will show the difference.

While there is a hell of a lot I dont agree on with Mike Stewart of BRK, there is one thing I can agree on.. "If you cannot tell the difference between 2 knives of differing style and price then you might as well always go with the cheapest"

same thing applies here.. if you cannot tell or feel the difference between a flat or convex knife, then does it actually matter?

"Ok, so out of curiosity, has anyone taken a knife and made some cuts on a scale, then convexed the knife (while keeping the same edge angle) and made some more to see how much difference it makes? "

No, but I can only imagine that it will directly relate to how much thinner, and how quickly the angle behind the apex is reduced. Many materials such as rope probably wont care if its a thinner convex behind the edge, or a thinner flat relief cut.


Cliff:If you keep the same edge angle what exactly are you doing while convexing?

LoL.. If you are being literal, then you are thinning the blade More than it was, but less than if you used a flat platen to thin it.. ergo.. attaining more cutting ability than you started with, and more ability to determine cross sectional strength in a graduated way than if you just flattened the steel behind it.. certainly you can just create primary, secondary, tertiary.....x(n) flat bevels to acheive the same, but will it look as nice? smiling smiley

A large part of the issue with the convex debate is too many people saying things like "The convex is thicker and stronger and designed for axes" Where-as the reality is that for any starting angle a convex results in less steel and a thinner overall cross section for the same starting angle and durabiliity. So my point (as a convex lover obviously) is that if you are going to create a bunch of flat bevels in varying angles and thicknesses, why not just convex it? its like creating facets on a diamond and promoting flats, when if you do it long enough you will eventually get a spherical shape that is smoother anyway. Completely stupid analogy, but a wheel rolls better than a decagon.

I know I dont post here anymore.. I'm just too involved in other things.. I just happened to see my name here and wanted to offer my opinion..

If I dont get around to replying to anything, then no insult intended. Hope you are all well.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 03:56AM
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cKc
If you are being literal, then you are thinning the blade More than it was,

This is really the crux of the convex vs. Canadian grind debate with me. Someone starts with a FFG, then convexes it (is convexes a real word?) and then proclaims it cuts better... of course it does, you just made the edge thinner!

btw I have no doubt you can get your convex knives to cut better than my FFG knives... but this isn't saying much smiling smiley

Thanks for posting on this cKc. It's good to see you stop by the forum.
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 04:40AM
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cKc
LoL.. If you are being literal, then you are thinning the blade

Yes by reducing the angle of the grind in the area being ground.

The main issue which comes up regarding convex grinds is the lack of attention to the difference in cross section which only tends to come up in regards to convex grinds and single bevel grinds, that I find a bit curious.

If for example someone gets a knife with a 0.045"/25 dps edge and they add a relief bevel then even being vague they will say something like "I thinned the edge" and the more precise will say maybe "I thinned the edge to 15 dps". However if someone works with sandpaper or similar they tend to say "I convexed it". Well you could convex it and actually turn it into a bevel which is 0.045"/25 dps:0.015"/35dps which would make it cut worse, that isn't what they are doing of course as they reducing the edge angles in those cases generally.

There is an air of mysticism often attached to the bevels and one of the worst examples of the nonsensical behavior was illustrated by Hossom who was one of the largest promoters of convex edges who had no data to support anything, aside from some very vague second hand claims and if he was questioned on the nature of the bevels thickness/angle he would even comment as to claim you could not specify that with a convex bevel as they are a continuous arc.

Well derp, there are functions for that, this isn't the dark ages, but even without high school math you could simply give an edge thickness and approximate angle. It isn't like a convex bevel which sweeps from 12 dps at the shoulder to 18 dps at the edge is so dramatically different than a 15 dps flat bevel. Most users would not even tell those apart and unless you jig sharpen you can easily change angles by 1-2 dps when you sharpen anyway.

Hossom was also another great example of convex edges which cut horribly and were very difficult to maintain, just look at the Spyderco fixed blades he designed. The edges were very thick and the angles very high, convex or not there was too much metal there. I even emailed Hossom about that and his only response was they needed the thickness to cut wood well - pretty interesting physics and the cross sections were the largest I have seen on awhile (extremely so).

Wako does a lot of convexing and he is fairly consistent in talking about the angles of his convex edges and how he increases the angle to increases the strength and lowers the angles to increase the cutting ability. However the viewers often don't tend to get this information and often walk away thinking that just scrubbing the knife to make a "convex" bevel solves all problems without consideration of angles at all.

I do wonder why no one takes this approach to flat/hollow grinds as there are makers who use both approaches to increase cutting performance, Tom Krein and Phil Wilson for example did regrinds and were very clear that when they were doing it the goal was specifically to reduce the edge thickness / cross section profile. Krien did hollow and Wilson flat but they both had the same goal, get the edge to the minimum thickness required to keep it stable.

And no one familiar with Krein's grind would look at a TOP's and think because it was also a hollow it would cut like Kreins because Krein was always clear that it didn't cut well because it was hollow, it cut well because it was so thin behind the edge. But you do see people thinking similar with convex/single-bevel grinds that the grind itself has an inherent set of properties which are not functional on the edge angle. Condor was one of the worse examples of this coming out with knives with 20-30 dps bevels but which were supposed to be functional as they were single-bevel.
cKc
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 06:35AM
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CliffStamp
The main issue which comes up regarding convex grinds is the lack of attention to the difference in cross section which only tends to come up in regards to convex grinds and single bevel grinds, that I find a bit curious.

Yes.. I think thats because of the fundamental problem with most people who are making convex knives not comprehending what they are trying to achieve. they simply "heard" that convex is a more durable edge and took the knife to a very slack belt.

I did this slideshow for a chinese MA forum a while back to discuss my view on convex bevels (they called them clamshells ) in relation to swords etc. The point was to identify 4 very basic concepts of a convex knife grind and the decision making behind the knife. The reality is that these 4 simplifications can cover an infinite assortment of "inbetweens" because the convex arc can decline at any rate, or staggered rates and too many people still dont understand whats really going on with the thickness behind the edge.


Most convex knives I've encountered (excluding Bark River) are ground like the 4th, and thickest example in this slideshow.





What you say about J-H's response is a little sad to me. I had held him in high regard from his input on knifeforums "sharpening" forum.

As to not being able to determine the angles.. thats kind of ludicrous seeing as its effectivly a < infinite series of vectors where the tangent and if you couldn't work it out, then writing CAD software to represent the arc in the first place would be incredibly difficult.


The biggest thing I've noticed with a lot of makers that I've spoken with about leaving about 0.03+ behind the edge bevel is literally related to fear of warranty claims and needing to cover the cost of damage and believing the thickness will protect the knife from abuse (which I guess it will to a point). or literally not even considering the thickness in the 1st place.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 11:40AM
A bit off topic, but thank you for that video and the slideshow Kylie. It was helpful!
Re: Posting Flurry Thread 1: Convex Edges
November 03, 2012 04:21PM
As far as I am conserved, convexing is mostly for getting a more obtuse apex while not affecting the general "macro grind". It's like adding a more obtuse bevel except it keeps the grind behind the edge thinner (for micro-bevel, you might obtain a comparable result by doing what some people call "back sharpening"winking smiley.

The "shoulder drag" problem is often cited. I'm not so sure about it. For small/micro bevel, I'd say it's barely noticeable. For larger bevel, it might play some role.
Re: Posting Flurry Thread 1: Convex Edges
November 06, 2012 05:46AM
Another "myth", in my opinion, about convex edges, which I saw all the time when I used to read forums like BF and KF was that convex sharpening is easier for a novice since you don't have to be as careful about maintaining a consistent angle. I'm sorry but this makes no sense to me. When sharpening on a soft backed medium, the way the apex is formed is dependent on both angle and pressure. Keep the same angle and press a little bit too hard for only one or two strokes and the medium can quite easily erase any gain you have made by sliding over the very apex you are trying to keep crisp. Having to keep both pressure and angle in mind as you sharpen seems to me much harder than just focusing on the angle. This is not to say that pressure doesn't make a difference in sharpening on a hard surface but it's effect has more to do with how finely you polish the apex and no real bearing on the angle of the apex.

My approach to sharpening is to take a DMT coarse or fine or extra-fine hone, depending on how dull the edge is and grind in a relief bevel. For me, even on my SAKs, I use something around 8 dps. Then I raise the angle a few degrees and use a finer hone, usually a hand-lapped Spyderco UF stone. Within just a minute or two my edge will whittle hair. Then as it gets dull I continue to sharpen with the fine stone at the higher angle until it takes more than a few minutes to re-sharpen. When it does I go back to a coarser hone and regrind the relief bevel. It is incredibly easy to tell when the relief bevel is finished by running a fingernail perpendicularly up and down the edge. What could be easier or more efficient than that?
Re: Posting Flurry Thread 1: Convex Edges
November 06, 2012 05:20PM
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cKc
Yes.. I think thats because of the fundamental problem with most people who are making convex knives not comprehending what they are trying to achieve. they simply "heard" that convex is a more durable edge and took the knife to a very slack belt.

Yes, it is just a superficial understanding which easily leads to wrong paths and propagation of nonsense when it is carried to extremes.

Quote

What you say about J-H's response is a little sad to me. I had held him in high regard from his input on knifeforums "sharpening" forum.

Hossom started out on BF with tests on his blades done by a guy call Gaucho who only cut soft media (flesh). Hossom argued that the deep cuts showed the power of the convex bevels and the high sharpness. As you know you can have very thick profiles cut flesh easily. Watch Lynn Thompson and Company chop up pigs, chickens and cows with all knives of machetes, swords and bowies. It doesn't take much of a knife to create large rents in flesh an even cut through fresh bone (which is under heavy tension). When Gaucho moved to other knives he found that even inexpensive v-ground AUS-6A blades could do the same thing - at this point I noted that all of Hossom's promotion could be limted to "My blades cut as well and are as durable as a $20 AUS-6A knife." . That is the raw truth, your extreme standard is not so extreme and it shows the severe danger of judging performance without baselines.

If his knives are used on hard targets they perform poorly, witness the results of the Spyderco versions where the thick edges with the very high angles (20+ degrees) do not cut well and people were having them reprofiled. The same blades of course would easily take large rents out of a chicken, but so would a felling axe as again the meat is hanging under tension and opens up under the cut just like if you cut a rope someone is pulling on, it is very easy to cut as there is no binding force on the blade.


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As to not being able to determine the angles.. thats kind of ludicrous seeing as its effectivly a < infinite series of vectors where the tangent and if you couldn't work it out, then writing CAD software to represent the arc in the first place would be incredibly difficult.

This is more along the line of "it can't be measured so you can't quantify it", i.e., there is no way to judge the performance from the specifications because you can't give them. Of course it is nonsense but you have to understand that most of the readers can't dispute this, hell I get asked all the time about how to calculate angles from width/thickness. It is just specialized knowledge that you have or don't, everyone has this in the area of their interest and is fairly ignorant outside of it. Hossom just plays on the ignorance of his readership - it isn't an uncommon thing in marketing.


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The biggest thing I've noticed with a lot of makers that I've spoken with about leaving about 0.03+ behind the edge bevel is literally related to fear of warranty claims and needing to cover the cost of damage and believing the thickness will protect the knife from abuse (which I guess it will to a point). or literally not even considering the thickness in the 1st place.

That is always a concern, the simple fact is that you only need your margin percentage wise to fail and then you break even. So if you run at a margin of 15% and you have 15% return then you make no money at all. And this doesn't even take into account the money you lose through loss of customers from press. However this isn't an unsolvable problem. What kitchen manufactures have been doing here is simply putting out "fine edge" lines and similar. These are knives from their lines which are ground to very thin edges and they warn that the knives are not for cutting hard materials. You can then choose to buy the robust line or the higher performance cutting line. Busse used to offer this as well that you could order a knife but if you were a bit more demanding you could call and ask for a thinner edge.


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theonew
Another "myth", in my opinion, about convex edges, which I saw all the time when I used to read forums like BF and KF was that convex sharpening is easier for a novice since you don't have to be as careful about maintaining a consistent angle.

The underlying assumption here is that you are trying to create a result, not necessarily the best one. If you take a knife and press hard into a soft medium then the edge will be ground. If you press too hard you will increase the edge angle, but for people who can't get a knife to slice a piece of photocopy paper they don't care about such matters they just want something that doesn't squash a tomato like on the Ginzu commercials. I do agree in general that there are more variables not less when you are using a soft media, but again this argument is made for people who can't sharpen at all and have no desire to learn how to.
Re: Posting Flurry Thread 1: Convex Edges
November 07, 2012 05:59PM
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CliffStamp


I do wonder why no one takes this approach to flat/hollow grinds as there are makers who use both approaches to increase cutting performance, Tom Krein and Phil Wilson for example did regrinds and were very clear that when they were doing it the goal was specifically to reduce the edge thickness / cross section profile. Krien did hollow and Wilson flat but they both had the same goal, get the edge to the minimum thickness required to keep it stable.


This here is the best straightforward statement that gets right down to the bare bones of it all right here.



Edited 1 time(s). Last edit at 11/07/2012 06:03PM by Ankerson.
Re: Posting Flurry Thread 1: Convex Edges
November 07, 2012 08:29PM
Video :





This video is long and a bit rambly, but you can clearly see Wako notes that the performance difference in the knives is due to the cross section. They are all convex at the edge but some of them are much thicker with higher angles.
Re: Posting Flurry Thread 1: Convex Edges
November 07, 2012 09:06PM
I don't frequent the other blade forums as much as some here do, so I don't have much of any insight into this... Are people arguing that a thinner edge doesn't cut better than a thicker edge?