Microbevel

Legacy Forum Archive advanced-techniques-and-sharpening-strategies
1

It is not my habit to link to other forums, but here Jon Broida, an accomplished sharpener, points out the advantages of a microbevel.

To quote from his post, the advantages are:

[quote]-maintaining extremely thin geometry on a knife that could not otherwise handle it
-reduce chipping in super hard steels
-increase stability in larger carbide steels (especially at low sharpening angles)
-improve edge retention at a cost of maximum sharpness[/quote]

I put microbevels on quite a few thin kitchen knives, particularly for reasons 1 and 4.

2

Yeah all of those are valid points… But rather than a micro bevel I believe that it is better to thin the entire primary grind (i.e. In murray carter’s terms, the “secondary edge”). Then you can put a thin edge on. So in essence you would have a 4 dps primary grind and an actual edge angle of 15 dps.

3

I like the advantages of a microbevel … if it’s mine.
Heck, my personals are all convex at this point, best marriage of strength and use IMHO … but I have the tools to maintain it.

If its for someone else and a particular angle with a microbevel, and they ask for it and its understood, yes.

4

[quote quote=“mark76” post=18103]
To quote from his post, the advantages are:

[quote]-maintaining extremely thin geometry on a knife that could not otherwise handle it
-reduce chipping in super hard steels
-increase stability in larger carbide steels (especially at low sharpening angles)
-improve edge retention at a cost of maximum sharpness[/quote]

I put microbevels on quite a few thin kitchen knives, particularly for reasons 1 and 4.[/quote]

Mark, I agree with the four points. I had some kitchen knives that couldn’t handle 15 dps (or at least they didn’t retain an edge long enough for my taste) so I resharpened to 20 dps and all is good (not a micro - did a complete resharpen to 20 dps). As these are very thin, tall, full flat ground blades I am wondering how a micro would be better compared to just sharpening the primary bevel to a more obtuse angle. With these blades I could not see the difference between 15 and 20 dps visually. But I could tell in edge retention. On other knives, thicker and not as tall, I can see a difference between 15 and 20, i.e. a Benchmade 940.

Maybe I don’t completely understand micros. To me it sound like the only advantage is #1, on a thick blade you can maintain thin geometry. To realized points #2, 3, & 4 you can get the same results with a more obtuse primary angle without a micro. Correct?

I would add this to advantages:

    • Fast and easy fix if the primary bevel is too acute and not working, adding a micro is much faster than a complete resharpening.
    • Is it easier/faster to touch up a micro? (I don’t know)

Is the following a correct assessment for points 1 -4? For example if we compare a 20 dps micro vs. a 20 dps primary bevel.
1 - advantage micro
2 - advantage primary at more obtuse angle - there will be more metal behind the edge
3 - advantage primary - same logic as above
4 - both are equal

Just throwing this out for discussion. I am definitely not an expert on micros, and have very little experience with them.

5

The topic has come up on this forum more often and as soon as we start talking about primary, secondary or microbevels confusion strikes :slight_smile: .

A microbevel is not a shallow and obtuse primary bevel. Instead, it is a bevel on top of the primary bevel, which then becomes the secondary bevel. A microbevel is effectively the third bevel on the knife; the blade face and the “normal” primary bevel (now a secondary bevel) are the other bevels.

The picture below (borrowed from another discussion somewhere on the 'net) explains it. The microbevel is what is called the primary bevel in the picture.

Forum member JDavis also explains it in this vid:

[video width=425 height=344 type=youtube]DmriTrx_qZo[/video]

If you create a microbevel it really only requires a couple of strokes on the WEPS using a high grit stone. Jon Broida doesn’t use a WEPS, but explains it quite well:

[video width=425 height=344 type=youtube]WYZmtDlwDi4[/video]

And here’s another video on microbevels, by forum member SmokeEater:

[video width=425 height=344 type=youtube]qmWoF6kjUXo[/video]

6

I think you’re right as long as we’re talking a thin knife (particularly fully flat ground) and a “Western” microbevel. Here we’re used to microbevels that are just a few degrees more obtuse than the “normal” primary bevel. However, according to Jon, in Japan a microbevel can be 30-40 degrees per side. If you’d put an normal primary bevel on your knife with that angle, it’d cut very poorly. This is also what part of my previous post refers to.

I don’t think so. It’s just as fast and easy to touch up a normal primary bevel, at least after the same amount of wear.

[quote]
Is the following a correct assessment for points 1 -4? For example if we compare a 20 dps micro vs. a 20 dps primary bevel.
1 - advantage micro
2 - advantage primary at more obtuse angle - there will be more metal behind the edge
3 - advantage primary - same logic as above
4 - both are equal [/quote]

I think you’re right, but advantages 2 and 3 of a single primary bevel come at the cost of cutting performance. Even though on thin fully flat ground knives this cost may be so little that you don’t notice.

7

I would suggest looking at adding a micro-bevel from this perspective :

Take any knife you have sharpened, doesn’t really matter what edge angle it on it, 10 dps to 30 dps, now think about what would happen if you reduced the sharpening angle and did a little grinding. For example, you have a kitchen knife sharpened with a 12 dps edge bevel which works perfectly fine in the kitchen, edge thickness is 0.010" . If you start grinding at 8 dps then what happens to the performance of the knife? That 12 dps angle is still there, you are just removing material behind it.

A micro-bevel is just one way to vary the geometry of the knife and in general a variable geometry will optimize performance. Take a piece of flat stock and grind a 10 dps single bevel on it and use that in the kitchen compared to a knife with a full flat grind (2.5 dps usually) and then a 10 dps edge grind, which one do you prefer and why? A micro-bevel just takes that another step further and allows you to reduce the apex angle without dropping the edge angle down so low it would ripple.

For example I can easily run kitchen knives with 5 dps edge angles, but usually run 15 dps micro-bevels. If I didn’t use the micro-bevel then the 5 dps edge angle would also be the apex angle and that would deform too easily. If I increased the edge angle itself that would be a tremendous waste because you don’t need the entire edge at the higher angle, just the apex.

It is no different for example than a distal taper. You run a distal taper because you don’t need all of that thickness in the tip and this is another angle then which optimizes the knife.

–

As an aside, increasing the apex angle doesn’t lower the sharpness, it doesn’t do anything to the sharpness at all because sharpness isn’t a function of the apex angle. Increasing the apex angle also doesn’t increase edge retention, it can easily decrease it depending on the apex finish and the style of cutting. For example :

https://www.youtube.com/watch?v=OSDFLgq4EDs

8

Good points here. I agree that touch ups are quicker with microbevel. On my japanese kitchen knives, I put 10 dps secondary bevel with 15 dps microbevel on WEPS, then do touch ups with a few passes on Spyderco Sharpmarker ultra fine stones. CliffStamp, how do you produce 5 dps angle on your knives?

9

Freehand, in most cases you will need to alter the primary grind itself in order to do that as 5 dps is low enough that if you don’t zero the primary the edge bevel can be massively wide.

10

this seems like some helpful information. Thanks

11

[quote quote=“CliffStamp” post=19735]
As an aside, increasing the apex angle doesn’t lower the sharpness, it doesn’t do anything to the sharpness at all because sharpness isn’t a function of the apex angle. [/quote]

I don’t understand… unless you are meaning it “scientifically”. But for all intents and purposes when you lower the apex angle (as long as you have a true burr free apex) then it will feel much sharper when cutting through any given medium…no?

12

[quote quote=“razoredgeknives” post=19760]

But for all intents and purposes when you lower the apex angle (as long as you have a true burr free apex) then it will feel much sharper when cutting through any given medium…no?[/quote]

It may cut better, it depends on what and how you are cutting, but that isn’t really what you take sharpness to mean. I can prove that to you with a few simple questions.

Lets say you looked at me and I was cleaning some pine pitch off of a blade and you asked what I was doing and I said I was sharpening it would you agree with me? It is likely you would not, but what about if I said “Well the knife will cut wood much better with the pine pitch off of it so therefore it is sharper.” Just like for example if I modified the handle so I had better control it would also allow me to cut deeper/easier but again would you agree that I sharpened the blade by doing that?

The actual meaning most people think about is actually the same as the actual definition in the literature, most people just have a hard time putting what they think into words. But that isn’t just about sharpness it is a problem with trying to go from how we think about things to some kind of rigid definition because we don’t actually think in those terms.

If I gave you a knife where the apex was rounded and you could easily move your finger up and down it you would likely call it dull. If I showed you that it could cut a carrot much better than a big bowie which was razor sharp you would not accept that the bowie was not in fact sharper you would likely say something like “well even a dull knife could cut a carrot”.

Here is the most simple illustration :

-grind an edge at 25 dps to the highest standard of sharpness you can achieve

-grind an edge at 10 dps to the highest standard of sharpness you can achieve, now make one cut right into a 1000 grit stone

Which edge is sharper, everyone will jump and say the first one.

Sharpness is a property of the apex, specifically a sharper blade produces a higher contact pressure at a given force. To look at it mechanically, when you cut there are a number of forces you have to over come :

-frictional losses
-direct mechanical losses (you have to compress or move some material)
-rupture (you have to break the material)

The last one is what sharpness controls. That is the technical term, but that is really what everyone means, the problem is when they try to make a definition they end up saying something that they don’t really mean. But again this is actually really hard to do. If you want to see how hard then try to define a game. It is pretty easy to keep listing things which are games but don’t fall into your definition. This problem is so hard because we don’t think the way we talk, if you try to talk the way we think it gets much easier.

13

Cliff, your points are well taken and I agree with what you are saying. But I still stick with what I said, “for all intents and purposes when you lower the apex angle (as long as you have a true burr free apex) then it will feel much sharper when cutting through any given medium”.

What you are arguing has mostly to do with geometry of the knife and edge retention. Will a lower angle have better edge retention? From what I have seen it depends when you pass the “critical” stage, i.e. the point where it will begin to lose effectiveness/retention and be too weak (like marthinus’ gayle bradley the m4 steel was good to around 11 dps or so).

14

So what’s the best definition of “sharp” that you have seen? I know we have discussed this before but it seems like a confusing topic lol :side:

15

This is confusing. But I think I get what he is saying.

And it coincides with what you said.

you can get a knife to feel and cut better with a lower angle apex but for how long during use will it stay sharp. I think what he is saying is if he took both them edges, steel being the same, abused them, the wider angle one would sustain less damage.

Is that right? Kind of what I took out of it.

to go along with this topic, I read somewhere where someone was talking about how some steels could easily be made razor sharp but during use, the razor edge would go away fast but the edge would settle down and still have a very sharp “working edge” for a very long time. Many of our carry knives are for working, cutting cardboard or rope and such..They still feel and are “sharp” but maybe not hair whittling sharp anymore after normal use but still very usable. The angle used depending on the steel and type of use all plays into this.

16

[quote quote=“razoredgeknives” post=19765]
[…]

Will a lower angle have better edge retention? [/quote]

It is critical here that you differentiate between push cutting and slicing as they are not dependent on apex angle the same way. Yes at some point the apex angle will be so low it will not have the strength and it will buckle, hence if you start decreasing the apex angle at some point the increase in slicing edge retention will reverse and at some point it will disappear completely. The same relationship is seen to a lesser extent in apex bevel thickness but in this case a lower thickness increases both push and slicing edge retention until the point it is too thin and it again collapses.

17

The main reason people get confused is because they meld sharpness and cutting ability together which leads into odd places when they start talking about things like edge retention which is how the sharpness changes, not the cutting ability.

All steels behave like this, it is just the math of how they wear. It comes out of the physics which at a basic level is due to the fact that the more blunt a blade is the harder it is to blunt it further. This when wrote as an equation has a solution which looks like this :

Sharpness (at material cut of length X) = Initial Sharpness / (1 + C * amount of material cut ^1/2)

In reality the power isn’t exactly 1/2 because of things like damage which are pseudo random in nature. I wrote an article on it a long time ago : http://www.cliffstamp.com/knives/articles/model_edge_retention.html .

18

[quote quote=“CliffStamp” post=19781][quote quote=“razoredgeknives” post=19765]
[…]

Will a lower angle have better edge retention? [/quote]

It is critical here that you differentiate between push cutting and slicing as they are not dependent on apex angle the same way. Yes at some point the apex angle will be so low it will not have the strength and it will buckle, hence if you start decreasing the apex angle at some point the increase in slicing edge retention will reverse and at some point it will disappear completely. The same relationship is seen to a lesser extent in apex bevel thickness but in this case a lower thickness increases both push and slicing edge retention until the point it is too thin and it again collapses.[/quote]

I agree… it’s just a matter of finding the balance of low enough to maximize both edge retention and cutting ability while yet not making the edge too weak.

19

[quote quote=“Zamfir” post=19780]This is confusing. But I think I get what he is saying.

And it coincides with what you said.

you can get a knife to feel and cut better with a lower angle apex but for how long during use will it stay sharp. I think what he is saying is if he took both them edges, steel being the same, abused them, the wider angle one would sustain less damage.

Is that right? Kind of what I took out of it.

to go along with this topic, I read somewhere where someone was talking about how some steels could easily be made razor sharp but during use, the razor edge would go away fast but the edge would settle down and still have a very sharp “working edge” for a very long time. Many of our carry knives are for working, cutting cardboard or rope and such..They still feel and are “sharp” but maybe not hair whittling sharp anymore after normal use but still very usable. The angle used depending on the steel and type of use all plays into this.[/quote]

this post Maybe will help you understand it a bit better… it did me because i’m visual lol

20

interesting. Never thought of it that way. the visuals do help.. I am also a visual person..lol.