400 % more edge holding - convex vs flat

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SharpPancake

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Please, please, please. I dont want to turn this thread to personal attacks and stuff like that (I think it will happened). I want a normal discussion.
Long time ago, I watched this video.
I know, Bark River and Mike Stuart again. But please, I dont want to read the same sh.t over again, how shady he is and so on. I want to discuss some thing that he said.

So, tl;dr version: he says, that a bit more obtuse convex edge has more edge holding as normal flat grind ,,scandi“. I think that is just nonsence. Even convex has a little V on the edge, so if you have 20° per side flat or 20° convex (made by slack belt) I think the edge holding will be the same.

What do you think?
 
I understand the point he is trying to make. But he is basically talking about grinds that have no secondary bevel. I also see where he is coming from when he says that a scandi is a low saber grind and that a convex blade is basically a rounded off low sabre grind. As for which system will cut longer, I don't know. Not sure where he gets info that a convex will cut 400% longer than a std sabre grind with no secondary bevel. I agree that convex is stronger and that it is easier to sharpen, though. I know that in the past people have compared edge styles so there may be a comparison already out there.
 
You can't make any comparisons unless you know the exact geometry of each edge. Just as a V edge can be any angle from a razor edge to an almost blunt edge. Likewise, a convex edge varies just as much.

But while you can measure the angle of a V edge, the convex edge has no angles. If you use a laser protractor, you'll see that the laser measures a wide range of angles along the convex edge -- the angle where a pinpoint beam of light reflects off a specific point on the edge and hits the measuring scale at a precise angle. The point just above or below that point will measure different angles.

On a V edge, that angle is consistent, a point corresponding to one specific angle. On a convex edge, the protractor shows a wide progression of individual angles that vary along the edge from apex to shoulder.

I really doubt that any specific convex edge has that much improvement over a V edge, but you'd have to be specific about the geometry of each.
 
We have had this discussion before and I had to admit at the time that convex isn't stronger if You just look at geometry.
On the otherside it cuts with less resistance than a flat with a bevel at the edge.
The convex sure has a stronger edge than a flat and zero grind Scandi/Mora (AKA low sabergrind).

Convex ground blades can have different convex curves and this greatly affect cutting performance and edgeholding.
If the top of the convex curve is closer to the edge, the edge will hold longer but cut with increased resistance through materia being cut.
Move the top of the curve higher will make the blade thinner behind the edge and cutting resistance will decrease.

The trick with convex blades is to find the proper curve for the materials they are used on.
Compare the average blade geometry between BRK and Fällkniven and it is obvious that BRK as a general, has the top of the convex curve higher up
on the blade than FK.
Thus BRK feels sharper and cuts with less force applied from the hand. but FK holds the edge longer.

How You want Your edge only You can decide by using Your sharpening skills.
Peter Hjortberger, owner of FK says that the more experienced the user is, the thinner the edge can be.

As for the video I agree with what Mike says, but I can't quantify how many % stronger the edge gets with a convex bevel on a "Scandigrind".:D

Hope this helps
Mikael
 
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Look, I get that there is a tradeoff to be made, and that going convex can be considered a good trade-off for edgeholding. But a few things irk me:

  • As far as I'm concerned, full flat is easier to sharpen, especially if you don't have a strop handy;
  • I definitely notice a difference between convex and full flat when carving wood. Yes, convex will carve wood too. Maybe some people will prefer it. But there is a big difference in how it feels (I have personally experienced this with a Bark River bushcrafter). I happen to prefer full flat, but I grant you convex will hold and edge longer;
  • I know convex will hold an edge longer, but if you are going to mention a percentage, especially something high like 400%, you better back it up with some testing or research;
  • Mentioning there's no such thing as a scandi grind because it's just 'a very low saber grind'. Well, I counter there is no such thing as a saber grind, because it's just a high scandi grind. Also, there is no such thing as a tanto point, because it's just a square spearpoint (which, by the way, is just an elevated sheepsfoot). Look, it's a sufficiently different thing, so people are going to call it something different. The same goes for the term 'scandivex'. You should be proud you did something that was different enough and succesful enough than people gave it its' own name.

Look, despite all the controversy, BRK makes some fine knives. This isn't enough to put me off of buying his knives (looking are a Kephart and a canadian special right now), but this rant was just quite annoying, to be honest.
 
Cobalt said:
I still have a hard time believing that a convex grind will outlast a v-grind at all, not to mention by 400%. I'd love to see the supporting data
Click to expand...

The V-grind will cut wood better, but as Mike says in the video the edge will fold over and need resharpening more often than the same knife with a slightly convex added to the edge.
I have experienced this many times in my work as a carpenter and before I put a new Mora to work, I adjust the edge to avoid carbide fallout.
If You make a convex edge with a zeroedge, the same thing will happen:
The zeroedge will bent over, or microchip.


Regards
Mikael
 
Too many variables to say 100% for any grind or edge. I’m sure 400% difference is possible from one end of the spectrum “worse to best” case.

Personally, I started applying a convex to all my knifes the last two years just how I sharpen now using leather strop and compounds.

I can’t say if the convex edge is really better or not I just needed to improve my sharping skills/equipment so made the $$$ investment and time investment to learn. I’m happy with my results the last year.
 
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Mikael W said:
The V-grind will cut wood better, but as Mike says in the video the edge will fold over and need resharpening more often than the same knife with a slightly convex added to the edge.
I have experienced this many times in my work as a carpenter and before I put a new Mora to work, I adjust the edge to avoid carbide fallout.
If You make a convex edge with a zeroedge, the same thing will happen:
The zeroedge will bent over, or microchip.


Regards
Mikael
Click to expand...


Makes sense, but not 4x sense ;)
 
Personally when it comes to chopping wood I'd say convex holds up better. IDK about 4x better but maybe 2x better.

For draw cutting or variety use I don't think it matters. I find it a lot easier to make a coarse drawing edge on a compound bevel over a convex bevel.

For woodworking tools a flat bevel with a small micro seems to work best. A slight convex of a degree or three from the shoulder seems not to matter but I don't think it helps.
 
Edge retention wise v grind is mostly better. Depending on what your cutting edge holding is better convex. It all varies though.
 
These tests can be skewed anyway you want.

If you have a clear, soft-wood log, a racing axe will go through it like butter. It has a very acute edge and geometry designed to clear chips without sticking.

Use that same axe on a knotty hemlock log, and you'll destroy it. A hardware store axe would do better.
 
Good lord what a bunch of horse hockey.

First of all, while it's true that there's no literal "Scandinavian grind" in a traditional sense (Scandinavian/Nordic nations have produced knives in a wide range of edge configurations, but most of them were not the grind we now call a "scandi", nor were the exclusive nations to produce knives with such a grind) the term has a distinct meaning in today's industry. It's a shorthand term used to describe a flat zero saber grind, with or without a microbevel (a true microbevel, meaning you can't see it without close scrutiny under bright light.) The term "scandi-vex" was developed to denote grinds that are otherwise like a "scandi" grind but are convex rather than flat.

Dulling occurs via two modes: abrasive wear, and plastic deformation. Thinner geometries are more susceptible to damage from plastic deformation (nicking, rolling, buckling) but hold an edge longer under abrasive wear. Thicker geometries are more resistant to plastic deformation, but dull faster under abrasive wear. The scandi grinds on common Nordic knives are typically done at pretty low angles--Mora uses 11.5° per side with a microbevel (except their woodcarving knives, which are full zero) which is why a lot of folks seem to think they're great in the kitchen (they're not). The zero flat saber grind gives you the thickest possible geometry when stock thickness and edge angle are held constant (barring zero hollow grinds because those don't realistically exist outside the theoretical realm for most tools.) The advantage of this configuration--thick grind, thin edge angle--is that the edge is given the maximum lateral support it can have for that edge angle, so the edge can be brought to very low angles while still resisting torque on the apex when breaking from a cut during wood carving and other similar tasks.

Convexes are not easier to sharpen than flat-ground edges. You can sharpen both the exact same ways. The chief advantage of a convex edge is that it's thinner at the shoulder for a fixed edge angle and stock thickness, like it was just clipped off straight and then blended in smooth. If it's stronger, it's because you've got a thicker edge angle, in which case you could do the same thing with a flat ground edge.

He talks about carbides getting rocked out of the edge. When cutting resistant materials, a push-cut is usually used. Push cuts benefit from a highly polished edge, which reduces slicing aggression but improves edge holding in pushing cuts. High carbide steels generally are best used with a fairly coarse edge, which improves slicing aggression and edge retention in slicing cuts, but is more prone to collapsing in pushing cuts, while fine-grained steels are generally more appropriate for bringing to a high push-cutting polish. So it makes me wonder why someone would choose a scandi grind of any variety in high-carbide steel, because it's basically the worst possible slicing geometry.

I strongly suspect that the reason for choosing a low convex saber grind over a flat geometry is mostly because from a production standpoint when hand-grinding it's way easier to make bevels look cosmetically even compared to flat grinding. You can fudge the shoulder on a convex easy as pie, even if the specific arc and thickness of bevels between sides are different from one another. Flat scandi grinds are easier to produce via automated machine grinding with jigs and fixtures, which is why they're a relatively modern phenomenon. Hand grinding on grinding wheels historically tended to produce a convex due to slight fore/aft shifting of the hands during grinding, even when (simple) grinding fixtures were used for holding the blades.
 
Cobalt said:
Certainly true when comparing V to V of diff angles. But what about V to convex.
Click to expand...

As others have stated above, there is a lot going on here. The basic principle is that 'thinner cuts better'. So the goal for every knife and knife maker should be - "go as thin as possible while still holding up for the hardest use this blade will see".

I was just stating above that low angles cut better, whether it's convex or V it doesn't matter. What Mike is pointing out in the video is that, for wood processing if you go with too low of an angle then the edge will not be supported enough and will deform or chip (depending on the steel). So he is saying that a flat grind of the same height will actually be thinner behind the edge and cut better, but he doesn't believe it has the support to process wood (and he would be right with certain steels at certain heat treats at certain hardnesses - lol). To determine the best geometry for a specific task, Cliff Stamp has an amazing video on how to do this and it's spot on (see below)

flat vs. convex geometry... Theoretically convex should cut better because it doesn't have any shoulders right? The only problem with this is that, while it doesn't have any shoulders it generally has much more meat behind the edge (as Mike is pointing out in the video). Why does it have more metal?

I've been grinding knives for several years now. I have 3 main methods of doing convex, depending on how deep I want to go (i.e. how much curvature). If I want it really obtuse (a LOT of curve and metal behind the edge) then I will use a slack belt. For medium curve I will use a soft platen, and for a shallow convex grind (almost imperceptible) I use a rubber belt as a backing that spins underneath my abrasive belt. If I scribe a line mid way up the blade that I will grind to, the convex (in all three situations) will have more metal behind the edge than the flat grind to the same point. If you want a lower angle convex grind, then you will need to raise the grind height up towards the spine and then, yes, you can make it probably cut better than a flat grind - but not a flat grind at the same geometry.

What I have found that works REALLY well is a full flat grind with a convex edge blended into the flat grind (i.e. remove the shoulders w/ out all the metal in the primary grind). There are other benefits that wood workers can appreciate to a full height convex grind, but I believe that the primary one is probably that it is more beefy and won't penetrate as deep (when chopping) thus, not getting stuck.

Sorry for being so long winded lol

 
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