Re: Ceramic or 1000 grit stone for convex bevels???

Legacy Forum Archive thoughtstheoriesscience-related-to-sharpening
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Help me understand the goal here?

I get running a thin bevel and adding a steeper micro bevel to give the actual edge more stability, but where does a convex edge fit into the picture?

I’ve done lots of convex edges, using the mousepad technique, freehand. To me, it seemed like a “cheat” for my inability to hold both primary and secondary bevels to some (any) precise angle. A cheat that worked very well and compensated for my lack of skill. :wink:

But I don’t understand “why” you’d do this on a WEPS? Seems like you are adding a lot of work for no benefit.

Not criticizing, just trying to understand.

(and if the answer is ‘I just like convex edges’ that’s fine too :wink: )

Ken

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I moved Ken’s question to a separate thread, since it is about a different topic that might develop into a whole new thread. Ken refers to the following thread: http://www.wickededgeusa.com/index.php?option=com_kunena&func=view&catid=6&id=8534&Itemid=63

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B) Very good question!

There have been heated discussions on the (alleged) advantages of a convex edge on this forum and other forums.

Some people believe a convex edge is stronger than a single-beveled straight edge.

I have seen two plausible reasons for this.

[ol]
[li]A convex edge has more steel behind it than a single-beveled straight edge. (One might ask the question here: a single-beveled straight edge of which angle, but alas.)[/li]
[li]A convex edge starts rather blunt (at the edge of the edge) and then becomes steeper. The blunt part of the edge pushes material aside, so that the remaining part of the edge glides through more easily.[/li]
[/ol]

I don’t know which, if any, of these reasons is correct.

However, I can reason that if reason 1 is correct, a multi-beveled edge is just as strong as a convex edge, because it has a similar amount of metal behind it. (Either a little bit more or a little bit less, depending on how the edges are shaped exactly.)

If reason 2 is correct, a multi-beveled edge might either be stonger than a convex edge or not. It might be stronger, because angle changes along the edge are steeper. It might not be strong for exactly the same reason :slight_smile: .

I’d love to see some experimental or theoretical proof. Opinions are welcome, too :lol: .

4

[quote quote=“mark76” post=8550]
[ol]
[li]A convex edge has more steel behind it than a single-beveled straight edge. (One might ask the question here: a single-beveled straight edge of which angle, but alas.)[/li]
[li]A convex edge starts rather blunt (at the edge of the edge) and then becomes steeper. The blunt part of the edge pushes material aside, so that the remaining part of the edge glides through more easily.[/li]
[/ol][/quote]

3. Marketing? :slight_smile:

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Yeah, what Mark said…and a little bit of “I just like convex edges” lol! The aspect of less maintenance was also appealing to me. I’ve heard because of the reason Mark brought up, “..has more steel behind it than a single beveled straight edge…” that it stays sharp longer without having to touch it up.

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… but it stays “less” sharp, longer… Or so it would seem?

Ken

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The angle is everything, and is almost never addressed. On the WEPS, you get a sharper edge, faster with a “V” grind, however, with such precision, the point of the apex of the edge will be rather thin and less stable (What I call the pencil point theory).

Convexing rounds the edge of the edge over, making it more obtuse at the apex of the edge, which gives it more geometric stability.

But the angle is everything - the precision from the WEPS means that you actually need/can/should use a more obtuse angle for a more stable edge than someone sharpening freehand because the flaws of freehand require thinner edges to account for the rounding.

Does that make any sense? :dry:

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It makes sense, but more so in a case where you are doing something that will make the knife steel fail at your chosen angle. If we are talking mostly about wear, there is more to look at, I think.

I tend to think that a convex edge, done right, is a stronger edge, but as Ken mentions, it really dulls faster. It is what I prefer for heavy duty cutting tools… Kuhkris, machetes, etc. It makes sense if you think about the geometry, a convex edge is thicker right behind the edge, as the edge wears or folds it gets thicker faster too… hence more dull more quickly.

If anything, unless you are OK with a dull edge, you need to do more maintenance. When you do this, it is also more work to get it back than the V.

A more acute “V” will tend to be thinner right behind the edge. Unless you apply force that exceeds the steel’s ability to take it, as the edge wears, it will be sharper longer.

Now this is all theory, I don’t have micrographs to prove it, but it fits well with my experience. I convex the edges of all of the knives that I will use for chopping or heavy duty cutting of any kind. They definitely lose the original slicing ability quickly, but they take lots of abuse and edge integrity is maintined… and they stay good enough for chopping tasks. I wouldn’t use them for making feather sticks… after a few cuts on something else.

I have done some kitchen knives on the belt grinder (lots of them for cutomers, they love them…not as picky as me) ..off platen, slack belt. This gives a nice convex edge which will push cut tomatos, but it doesn’t stay that way long at all. The same knife at 17 degrees on the WEPS with a fine microbevel at 20 to 22 degrees (half dozen or so strokes with the 1200 ceramics) stays sharp considerably longer. It may not survive an encounter by a ham handed knife weilder with a hard bone as well as the convex edge… but I really try to avoid that :slight_smile:

The V is also easier to touch up than the convex edge. Usually a few strokes on a bench strop with 3 micron paste for me brings it back nicely. The convex edge needs a second visit to the bench grinder…

To wrap it back to what you said Tom, I tend to think the results with a more obtuse angle will also lead to a more significant loss of sharpness more quickly than a more acute angle…if y we do not exceed the steels abilities… of course.

Phil

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Ah very interesting, so I misunderstood then. So with that being the case, what about a single 5 degree micro bevel…would that dull quicker than a V edge, like a convex does?

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Probably, but it is a mattter of how much microbevel is applied. My idea is to add a bit of “tooth”, but not take much metal off of the edge. A few light strokes will not change the bevel geomtry very much.
But if you want to carry what I said to the final analysis.. of course you are right. The edge would lose that very fine edge faster…

I read about Clay doing something smilar for some knives that he has used for skinning. He liked the results. Lots of folks also like the tooth for food prep too. A very polished edge can be les effective for cutting fiberous material. I think that the small bit of roughness that is added at the edge seems to aid in cutting through the skin of vegetables. I guess Clay likes it for hide too, as he mentions skinning game with this method of sharpening.. So I tried it, and I like it too! I don’t dotice a huge difference in edge retention, and the 3 micron bench strop easily adds a little bit of the tooth back..
:slight_smile:

I think you should see how the convex edge works for you in your application. This is really the key… fitting the edge to the steel, its use…and your cutting habits. The nice thing about having the WEPS is that ist is not that hard to try different things. You can easily put a V back on that knife and try that. Also, maintenance is lots simpler with the WEPS than trying to do it by hand. Much of the common wisdom about the “cost” of maintenance has to be reconsidered because of that.

The more you experiment, the faster you learn. I always try to listen to others and learn from them, but prove it for myself… on my knives and the way I used them.

Phil

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So far convex edge been depicted as V bevel fits inside C(onvex) bevel and with the same shoulder height (apex to where bevel end). On the opposite end, where C fits inside V, therefore C blended shoulder will be higher on the blade (more height). So C.in.V will have virtually the same angle at apex.

To me convex is more about no abrupt shoulder transition and bevel curvature. Curvature where could be optimize for max flow through material - think what shape a submarine/bullet/airplane-wing/etc yup mostly convex. I do micro-bevel my convex edge, angles depend on steels. Most of my edges (C and V) are too thin for steels anyway. Indeed blade with thicker behind the edge dulls faster -> geometry dictate that. Not so much about V or C, IMO. A common C probably intersect V some where near mid-point however C shoulder still higher than V.

Rocco’s question about micro-bevel as a 2 S(egments) C(onvex). Note - SC apex is higher up in blade than apex of V. The dull rate of SC & V is the same when the damage (deformation/fracture) at or above the micro-bevel shoulder. If damage is short of SC shoulder, then performance of both SC & V proportionally degrade, merely more apex (flat top) resistance and proportional less bevel resistance.

Clear as mud :stuck_out_tongue:

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[quote quote=“BluntCut” post=8569]
To me convex is more about no abrupt shoulder transition and bevel curvature. Curvature where could be optimize for max flow through material - think what shape a submarine/bullet/airplane-wing/etc yup mostly convex. Clear as mud :P[/quote]

When you are talking about the shapes you mention, keep this in mind, thos designs are done using fluid dynamics as the basis. We typically are not cutting fluids nor gasses. The sharpest things I know of, microtome blades and obsidian scalples, used to part relatively soft solid material very cleanly and with low effort, they do not use a convex edge.

This is an interesting quote that sort of talks about cutting real world solids:

Jay Fisher
http://www.jayfisher.com/index.html

What contributes most to the amount of friction encountered in cutting is the
actual blade grind rather then the bevel… or so I think. This would be true especially when cutting anything with a thickness that is an appreciable percentage of the blade height.

Yes, your explanation is clear as mud… but I think I got what you said anyway…
:slight_smile:

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[quote quote=“leomitch” post=8571]Hey Mark
I loved your blogs on the convex edge, excellent work my friend!
I wonder if this isn’t good spot to pop in a little history of the convex edge.
It is probably the oldest method of sharpening around. Even in the early times of metal blades a la the bronze age, the easiest method of sharpening for the common fellow was to sit in his camp during the early evening passing his blade edge along a handy stone of suitable hardness creating or rebuilding the sharpest edge he could manage in the simplest way available. Another time stopping by a rocky stream tumbling down a mountain side for a drink, he might pause in his travels and again work on that edge. As Ken pointed out, a convex edge is a bit of a cheat since it is impossible to guarantee the angle when sharpening this way manually, but eventually the edge would obtain that wonderful bullet shape ogive that gives one a substantial edge for heavy duty tasks…for this bronze age fellow chopping wood, blazing a trail through those ancient tractless forests, killing and rendering after hunting down some animal or another and lets not forget self defense, for cleaving through bone and armour when the occasion arose.
For the guy who sharpens by hand , it is the natural product of sharpening and stropping manually daily, eventually the convex edge will appear.
Using the modern tools like the WEPS as Mark has described so beautifully in his blog, makes the building of this kind of well supported edge an easy task and it can be maintained easily and for a long time simply by stropping on something handy, be it a piece of leather with or without compound,on your jeans, a piece of sandpaper or even a piece of newsprint. Using any of these will keep that excellent round shoulder and ogive sharp and ready for cutting, slicing, chopping and whatever. Hopefully though, not for cleaving through armour and the bones of enemies! LOL!
So down through the ages the convex edge has been the useful companion of the ordinary man, simple and reliable…not always super sharp at first, but eventually through daily stropping, it becomes a strong and very sharp edge. An axe is an excellent tool that utilizes a convex edge and one can see in this useful tool a convex edge working at its strongest and finest.
Enough? I guess so, I do go on yes? :huh:

Leo[/quote]

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Thanks Leo,

Hope it’s okay I brought this over?

You put into words what I’d always thought about convex edges. Heck, when I first started sharpening around age 8-9 I managed to convex my knife, and I didn’t even know the word “convex” back then. Freehand on a cheap composit stone, it just happened. It didn’t help that the stone got badly dished out, I didn’t know the word “lapping” back then either :wink:

Anyway, for a knife you’ll keep in the field and touch up by hand, I can see the use.

And I agree that whacking tools like them. My Granfors Bruks has a lovely convex edge.

As to the earlier statement of C inside V or V inside C, I’m not sure I agree with it. I guess I need pictures, but it seems either way the angle will be greater with a convex edge. Granted, you can mitigate this on a slicer by keeping the whole structure thinner, but it will never be as “sharp” as a pure V. And then we start getting into the micro convex (like a micro bevel) This has been discussed as rounding the edge while stropping. Generally referred to as a thing not to do but it may have it’s place? No idea, really, just thinking it over.

Regardless, it seems trying to intentionally create a convex on the WEPS, setting 4-5 different angles along the way is way more complicated than putting a simple V on the knife and unless you’re then maintaining it with a hand stone in the field, more work to maintain as well.

Great discussion guys,

Ken

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Thanks for moderating, Ken. I’ll recommend you to Clay :wink: .

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Thanks a lot, Leo! That puts things in historical perspective. I knew you are old and wise, but didn’t know you are that old :wink: .

It is interesting that you mention that a convex edge is the edge of choice on an axe. It is also used a lot on outdoor knives. (There was a reason I put it on my A1.) Interestingly enough it is not used a lot on kitchen knives. Would that say something about the use of a convex edge?

[quote quote=“leomitch” post=8571]

Enough? I guess so, I do go on yes? :huh:

Leo[/quote]

Can I stop you? :dry:

17

[quote quote=“PhilipPasteur” post=8574][quote quote=“BluntCut” post=8569]
To me convex is more about no abrupt shoulder transition and bevel curvature. Curvature where could be optimize for max flow through material - think what shape a submarine/bullet/airplane-wing/etc yup mostly convex. Clear as mud :P[/quote]

When you are talking about the shapes you mention, keep this in mind, thos designs are done using fluid dynamics as the basis. We typically are not cutting fluids nor gasses. The sharpest things I know of, microtome blades and obsidian scalples, used to part relatively soft solid material very cleanly and with low effort, they do not use a convex edge.

[…]

What contributes most to the amount of friction encountered in cutting is the
actual blade grind rather then the bevel… or so I think. This would be true especially when cutting anything with a thickness that is an appreciable percentage of the blade height.

Yes, your explanation is clear as mud… but I think I got what you said anyway…
:)[/quote]

Very interesting, Bluntcut and Philip.

I know little about fluid dynamics and how it compares to friction in a solid material (if anyone can explain me, that’d be great), but what strikes me is that indeed for cutting relatively soft materials (food, tissue) a V-bevel is usually preferred. And for cutting hard material (wood with an axe or an outdoor knife)) a convex bevel seems preferred.

18

I’m there for you, brother :wink:

Ken

19

[quote quote=“mark76” post=8587][quote quote=“PhilipPasteur” post=8574][quote quote=“BluntCut” post=8569]

What contributes most to the amount of friction encountered in cutting is the
actual blade grind rather then the bevel… or so I think. This would be true especially when cutting anything with a thickness that is an appreciable percentage of the blade height.
:)[/quote]

Very interesting, Bluntcut and Philip.

I know little about fluid dynamics and how it compares to friction in a solid material (if anyone can explain me, that’d be great), but what strikes me is that indeed for cutting relatively soft materials (food, tissue) a V-bevel is usually preferred. And for cutting hard material (wood with an axe or an outdoor knife)) a convex bevel seems preferred.[/quote]

After the blade cuts through the surface and penetrates more than the thickness of the bevel the sides of the material start sliding along the blade grind itself. For instance a full flat grind would have more of the main part of the blade in contact with the material at one time versus a hollow grind or a convex grind. If you are cutting something where a major portion of the blade is engaged with the material, the sides of the blade will contribute more friction or resistence to cutting to the overall effort required than the bevel. Maybe if you think about slicing an onion horizontally you will get the picture. If it is a large onion, at some point the entire height of the blade may be between the onion and the slice you are creating. At that point the sides of the knife contribute more to the cutting effort by quite a bit than anything done at the bevel.

I was reading more of that article that I quoted before. Jay Fisher was talking about his preference for hollow ground blades for combat knives, particularly because the blade geometry itself provides less resistence in slashing or slicing actions.At least in his estiamtion. Admittedly this difference must be very small, but then the difference of cutting force produced at the edge between a convex edge and a V is likely even smaller… This was the point that I tried to make initially.

Is that clear as mud ??
:slight_smile:

BTW, here are some links to papers done that try to develop a model for sharpness (in the first one) and cutting resistence as it relates to bevel angle (sharpness) in the second one. A little off topic, but interesting just the same.

http://www.ucd.ie/mecheng/staff_pages/pdfs/Gilchrist_2007a.pdf

http://www.ucd.ie/mecheng/staff_pages/pdfs/EFM_2010_Sharpness_II.pdf

I though Bluntcut would find these fascinating…

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I like mud! :wink: (and slurry!)

One additional thing (which is not actually very relevant but may be interesting to think about :wink: ) I’ve found rarely discussed is the moisture and texture of what you are cutting (speaking mostly of food here) and the overall bade geometry.

With a typical FFG knife cutting a firm moist substance, I get a lot of resistance from (what in the stropping threads we’ve termed stiction) the material.

Examples would be apples even more kohlrabi and even more sweet potatoes. The resistance goes off the charts as the cut goes deeper, regardless of how sharp the knife is.

One thing I’ve noticed here is using a thinner (spine to edge) knife with (essentially) parallel sides seems to make a huge difference. An example would be an Opinel carbon paring knife (only cited because it’s one I use for this solution).

I think this is what some companies are trying to address when they put dimples or bumps on a knife’s surface but I’ve never found those actually helped much.

We now return to our regularly scheduled discussion of convex edges…

Ken