PDA

View Full Version : Bevels... Difference between AS and symmetric bevels



jgraeff
08-25-2011, 12:59 PM
So I'm curious to find out what the edge retention and performance differences between different bevels if any have experience with them.

My misonos are all 70/30 most of my other knives are 50/50 except my honesuki came with a 90/10.

Can you guys explain about what makes them different?

tk59
08-25-2011, 01:45 PM
Introducing asymmetry in your bevels is a way of thinning your blade near the cutting edge without lowering your bevel angles excessively and causing weakness in your edge or in extreme cases, failure to even form an edge (it would just crumble, leaving large chips in the edge). The trade-off is a "steering" effect that is caused by unequal forces acting on either side of the edge. The side with the larger bevel would encounter a larger force resisting the cut and so the blade would tend to veer away from that side. To counteract this effect, the angle at which the large bevel is ground can be lowered relative the the small bevel to more evenly distribute the forces.

jgraeff
08-25-2011, 01:54 PM
ok so that makes sense. so if i got this right on a right handed blade the right side being the predominant side should be slightly lowered, and the left side should remain the same angle?

what about a microbevel on AS edges?

tk59
08-25-2011, 02:00 PM
If you feel you want to keep your edge thin but add even more strength, you can add a microbevel to anything and it can be a single extra bevel at a higher angle or it can be two extra bevels depending on how you like your edges to perform. When I apply a microbevel, I will generally add a tiny bevel at a large angle (25-60 deg) on the right side only for a right handed knife.

I don't do this for AS, in particular but mainly for knives that are exceedingly thin at the edge (single bevel or ultra thinned knives), blades that are hardened to the point they lose their toughness (for AS I might put a micro on anything over 61 hrc depending on the user), blades made of very high carbon steel (significantly more than 1%) since the high carbide volume will lower the stability of the edge or blades where the carbide size is fairly large and will simply not form a decent edge at 10-15 deg on a bevel (conventional German knives, for example).

jgraeff
08-25-2011, 02:11 PM
Ok good to know, i have actually noticed that with a coworkers knife, some german made knife, i sharpened it and it was super sharp, i then applied a microbevel and it was significantly duller than before had to redo the entire process but it wouldn't handle a microbevel for some reason I'm guessing the steel.

but i always add a microbevel to my misonos about 45 deg or so, and i haven't noticed an ill effects to far, i also add one to my Kono HD since i use it so much.

Which knives are best to have an AS edges on?

tk59
08-25-2011, 02:20 PM
By AS, you mean asymmetric? For future reference, AS always means Aogami Super/Blue Super. Asymmetric edges are good for single beveled knives of any kind. Jon puts a micro on Suisin Inox blades (19C27 is pretty high carbon and it is pretty hard on that line). HOWEVER, it really just depends on how much you've thinned it compared to what it can take. That, in turn depends on what the user does with it. This is one of those questions that is subjective and user-specific. For example, I hardly EVER use microbevels on my own knives. I'm pretty gentle with them and it's nice when I actually get to sharpen them. I have a friend, though who is a pro and is pretty careless with his knives. I use microbevels on EVERYTHING for that dude.

For those of you on the forum who think I might be talking about you on that last part, I'm not. :D

Benuser
08-25-2011, 07:13 PM
Which knives are best to have an AS edges on?

I would say knives with asymmetric blades! Most Japanese knives I've seen had a convex front (right, with kanji inscription) blade and a flat back. The front side has a very large convex bevel while the back almost none. Typical would be the front being sharpened at eventually 10 degrees, and the back hardly sharpened but just stropped at 15.

jmforge
08-25-2011, 08:09 PM
I am a bit confused. How does shifting the edge over a bit allow you to thin it and maintain more edge strength/stability? I kind of understand why the Japanese may single bevel knives with a hollow grand backside, but I am having trouble figuring out the 70/30 type grinds.

tk59
08-25-2011, 08:48 PM
I can't draw it for you right now but if you draw bevels at the same angle as shown in the first edge and the second to last edge (going from left to right) here: http://zknives.com/knives/articles/knifeedgetypes.shtml, you will see that the thickness of the knife within the bevel is thinner behind the edge for the asymmetric version.

jmforge
08-25-2011, 09:01 PM
In those pics, it actually looks thicker to me. I can see how leaving more of the "short" side of the blade flat would mght you a similar effect to a chisel grind, but I'm still not seeing how actually it gets the part right above the edge thinner.
I can't draw it for you right now but if you draw bevels at the same angle as shown in the first edge and the second to last edge (going from left to right) here: http://zknives.com/knives/articles/knifeedgetypes.shtml, you will see that the thickness of the knife within the bevel is thinner behind the edge for the asymmetric version.

tk59
08-25-2011, 10:48 PM
I didn't tell you to just look at the figure in the link. If you read my post carefully, it says "draw the bevels at the same angles." The drawings in the link have different angles.

jmforge
08-26-2011, 12:09 AM
Okay, did that. Maybe it can be blamed on my poor drawing skills, but when I did it, the thickness above the edge appeared the same on both, but I used the same angles for both types of edges. Are you saying that you can reduce the angles when you go with 70/30?
I didn't tell you to just look at the figure in the link. If you read my post carefully, it says "draw the bevels at the same angles." The drawings in the link have different angles.

jmforge
08-26-2011, 12:16 AM
tk,don't get me wrong. I am not trying to argue. I am genuinely curious as to why this setup seems to work better for certain applications. I know that a scandi grind with a zero edge works better for wood carving. One thing I was wondering about is if a right handed person uses a knife that is assymetrically ground for right handed use if they might somehow be putting less lateral stress on the edge which would allow it to be ground thinner and still hold up? I am starting to get an idea why having the flat side of a single bevel blade up against the food you are cutting would work.

jgraeff
08-26-2011, 01:18 AM
By AS, you mean asymmetric? For future reference, AS always means Aogami Super/Blue Super. Asymmetric edges are good for single beveled knives of any kind. Jon puts a micro on Suisin Inox blades (19C27 is pretty high carbon and it is pretty hard on that line). HOWEVER, it really just depends on how much you've thinned it compared to what it can take. That, in turn depends on what the user does with it. This is one of those questions that is subjective and user-specific. For example, I hardly EVER use microbevels on my own knives. I'm pretty gentle with them and it's nice when I actually get to sharpen them. I have a friend, though who is a pro and is pretty careless with his knives. I use microbevels on EVERYTHING for that dude.

For those of you on the forum who think I might be talking about you on that last part, I'm not. :D


I actually didn't know that but thanks TK, I do get what you mean by user-specific, I'm just trying to get a better understanding of how bevels and steel work together so that i can understand more and then apply the knowledge to my knives and applications. I love these forums because there are so many helpful experts out there.

Now that I'm thinking about it, are there any good books to get as references for these types of questions?

sally benes
08-26-2011, 02:23 AM
Okay, did that. Maybe it can be blamed on my poor drawing skills, but when I did it, the thickness above the edge appeared the same on both, but I used the same angles for both types of edges. Are you saying that you can reduce the angles when you go with 70/30?

This might be totally off-base but we had a conversation about this over dinner and my oldest seemed really interested. After dinner he showed me this link: http://www.knifeforums.com/forums/fbbuploads/1304044520-AsymmetricalBevels.jpg. He told me the angles on #1 and #3 were the same. Then he took a ruler and showed me that the going up from the very tip, the one that isn't even was narrower once you got past a certain point. Is this what you guys are talking about?

wenus2
08-26-2011, 02:31 PM
Is this what you guys are talking about?

It is, good link.

El Pescador
08-26-2011, 03:28 PM
Sally you've been on the board for 2 days and figured this out! Great link, btw. Keep posting!

jmforge
08-26-2011, 04:31 PM
My ruler is not giving me the same results. With equal bevel angles, all you are doing is shifting the edge to one side, you aren't removing any more or less steel as best as I can tell. I'm still curious about whether having the LONGER bevel on the side where the slice is has some effect? this strikes me as another one of the unquie questions about kitchen knives. Conventional wisdom says that partial height grinds, be they blended or not, make for a greater bevel angle than a full height grind for a given blade thickness. My impression as that kitchen knife blade geometry is all about striking a very delicate balance between getting as thin an edge as possible using a primary bevel geometry that also doesn't let food stick to it so easily. A bit tricky to say the least.

Benuser
08-26-2011, 04:46 PM
The front's large, convex bevel without any shoulder avoids the wedging that is common with a V-shaped edge.

Benuser
08-26-2011, 05:23 PM
The effect of the asymmetry is to be observed while cutting: if you turn the knife a few degrees clockwise you will obtain a straight cut.

One of our great sharpeners once wrote a report about inverted edges. If I remember well the result was that the knife turned counterclockwise when used by a righthanded.

Benuser
08-26-2011, 06:14 PM
I've to correct: the wrong sharpened knife twisted the edge to the user, so it turned clockwise, instead of counterclockwise, as I wrote.

JBroida
08-26-2011, 06:36 PM
My ruler is not giving me the same results. With equal bevel angles, all you are doing is shifting the edge to one side, you aren't removing any more or less steel as best as I can tell. I'm still curious about whether having the LONGER bevel on the side where the slice is has some effect? this strikes me as another one of the unquie questions about kitchen knives. Conventional wisdom says that partial height grinds, be they blended or not, make for a greater bevel angle than a full height grind for a given blade thickness. My impression as that kitchen knife blade geometry is all about striking a very delicate balance between getting as thin an edge as possible using a primary bevel geometry that also doesn't let food stick to it so easily. A bit tricky to say the least.

why not just try a few of the different grinds in the picture and see how they work? That would be a quick and easy test to do.

jmforge
08-26-2011, 06:54 PM
I plan to do that Jon, but it would be cool to try to find exactly out why they do what they do. That way you might be able to get a better idea of what kind of variations on the theme you might want to try out.
why not just try a few of the different grinds in the picture and see how they work? That would be a quick and easy test to do.

JBroida
08-26-2011, 09:02 PM
i think if you try it, the why it works will be a lot more clear

tk59
08-27-2011, 01:46 PM
*******: The only other effect that I can think of is some people (like me) make the inside bevel (left side for a right-hander looking down at the spine of the blade) tiny on some of their knives in order to get more precision on very thin cuts.
sally: That one is better than the one I found and works out nicely without having to redraw. Kudos to your son. How old is he, if I may ask?
Pesky: Let's give credit where credit is due. She said her oldest son found the diagram but for all we know, someone from the dinner table might have supplied the insight beforehand.
Jon: +1. There are so many different variations on asymmetric bevels and every knife will handle a different level of thinness, different types of tasks may call for a different edge geometry, not to mention the method by which the task is being performed.

El Pescador
08-27-2011, 06:27 PM
I stand corrected TK. My apologies to Sally.