Convex Grind - Issues?

Convex blade edge is the major reason why I bought Fallknivens knifes.
 
Having used convex edged knives for a long time now I feel he may be missing something here ?

Some of my best cutting knives are convex edged.
 
Here are a couple more things he says on that page I disagree with:

stropping a cutting edge should only be done by well-practiced professionals.
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Nonsense. It's not hard to learn and it's a useful skill. The only risk you take is that you might round the edge and have to spend a whole minute tops fixing it.

Here is the truth: sometimes you want a cheap, throwaway knife. Factories can supply these for you. Buy them at a garage sale, you'll get a lot better deal, and you'll keep more of your own money. But when you want something more, when you want a good knife, a custom knife, a fine knife, or an investment knife, there is only one group of people that can supply your needs: custom knife makers.
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Wot wot? It's not possible to get a good knife from a production company? Is he really serious?
 
Well, don't forget, he's also a salesman that's selling his particular style of knives.

Although I agree with some of what he says, several of his statements, like all/most factory knives are basically junk that can't cut + never go up in value, are just flat wrong.

As far as convex grinds/edges go, he's seems in favor of mirror polishes + gun bluing as a knife finish.

I'm guessing the convex edge, with it's sandpaper/mousepad sharpening method isn't exactly complementary to mirror polished steel (especially when blued.)
 
i put a convex on the chopper i made for brian jones. i havent made it fully razor sharp but its not far from it. i have chopped osage orange, red elm and some white ash with no visible dulling. i made up a test blade with a convex grind that i done some testing on to see how much abuse it would take. it held up good cutting 3/16" brass rod before making it razor sharp.
when i did make razor sharp it would have done just as well if the rod didnt fall off just as i was in mid swing. the hammer head hit the edge but only chipped it a little bit.
i started out making convex grind knives and was cut bad by a big bowie i made that had a convex edge. i have always been a fan of a convex edge.
 
hlee said:
Just for the record, given equal inclusive edge angles at the very edge, a convex edge has LESS metal behind it than either a flat ground or a hollow ground blade. A convex edge has more metal behind it than a flat ground or hollow ground edge ONLY if the edge angle is more "obtuse."

If this does not make sense, draw three "V"s, one straight, one convex, and one concave, all with the same "apex" angle, and see which one makes the fattest V.

Convex edges are considered stronger only because they are more "obtuse."
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With your assumption you would end up with different thickness of the blade for each grind...

If you stick with a piece of metal with equal dimensions and just apply different grind:

grind-1.jpg
 
huugh said:
With your assumption you would end up with different thickness of the blade for each grind...

If you stick with a piece of metal with equal dimensions and just apply different grind:

grind-1.jpg
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That also works off the presumption that the flat and hollow grinds are zero bevel, generally that is not the case.
 
My hollow ground knives are very sharp, my spydie kitchen knives are the sharpest objects I have ever seen!

I keep my knives very sharp and the thinner hollow ground knives will incur edge damage with just normal use. Oh they still cut good but if you look at the edge in the light or cut fuzzy material you can detect imperfections.

Heck, I can sometimes percieved slight dulling just from fingering the edge (sounds worse than it is).

My convex shaped blades don't wear like this. It's takes precious little to restore the edge. I notice this more with my barkies than my swamp rats, and between the barks. I can get the A2 steel sharper than their stainless although both are sharp. The mini canadian seems to cut everything equally good, the blade shape seems to make it unlikly to bind in stuff that sticks to other blades, like thick raw meat. Cutting cardboard seems to polish the blade. I am sure my howler is just as good, but the bark river knives come in a small size, and see more use. Lots more use.

I just got a couple of stropping blocks and it's changed my whole outlook on knife edges. I have dulled knives making an angle mistake while sharpening with a stone. It seems easiest to just follow the manufactors edge and maintain it.

You don't have to worry about angle using a stop. If you make a mistake, usually pressing too hard, you can easily fix it. I have also read a few post from people that have convexed their own blade so it's really not the end of the world if you have to do it, like you might be led to think.


My spydies are capable of greater sharpness than my convex knives but the convex edged ones maintain the sharpness with very little work.
 
Convex knives and stropping - it just doesn't get any better for real use knives! :thumbup:
 
huugh said:
With your assumption you would end up with different thickness of the blade for each grind...

If you stick with a piece of metal with equal dimensions and just apply different grind:

grind-1.jpg
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Not necessarily. Your assumption is in a full height (zero edge) grind. In this case you are comparing apples and oranges. The hollow will be a much better cutter because it has a much more acute angle. The same goes with the V-edge. Of the three shown in the above picture, the convex ground one will be the worst cutter of the bunch. It has the least acute edge angle (tangent to the curve of the blade grind at the apex of the edge).

Unfortunately, I have neither the skill nor the software to produce a picture of it, but you can start with the same stock and also give each grind the same edge angle (see above for definition), the difference would be in the height of the grind. The hollow would have the shallowest grind, the V-edge the next shallowest, and the convex would have the tallest grind- given the same stock thickness and the same edge angle. In this comparison, contrary to popular "wisdom" the hollow ground blade would have the most steel behind the blade, and the convex would be the "weakest."

Of course, the hollow grind would be best for shallow cuts, as it rapidly gets thick, and the convex the best for deep BECAUSE it has LESS metal behind the edge. Convex edges make good choppers because they have less metal behind the edge (less drag= less wedging= deeper penetration= better chopper) than an equally ground flat grind or hollow grind. However, they are ususally compared as in the picture above (full height- zero edge- grind, equal stock thickness). In this comparison, the convex will be the most "beefy" at the edge, but will also be the poorest cutter (least acute edge angle).

Think about how you make a flat gorund edge into a convex ground edge. (assuming not ground "zero edge") Most people advocate grinding off the "shoulder." Removing metal from the shoulder does not magically put more metal behind the edge.

Convex edges are great because they are easy to maintain, with just a bit of sandpaper and a mousepad or some leather for backing. However, they are also the extremes of the edge spectrum. They are either very good cutters and relatively weak (less metal behind the edge) compared to a V edge, or beefy but less acute (less good cutter) compared to a V-edge.

One of these days I'm going to have to make one of those snazzy pictures to illustrate my point.
 
3Guardsmen said:
You're right, Joshua J.!:thumbup:

Jay Fisher doesn't just make good knives, he makes freaking outstanding knives! I know, my dad's got one. Heck, the knife stand alone, which Jay also made, is a work of freaking art! That said, I think Jay ought to stick to making awesome knives and stop bashing "factories." That's a pretty broad brush he's swinging around. Though he didn't come right out and say it, I think his "ATS-55" rant was a dig at Spyderco, and to me, it just goes to show he doesn't know squat about Spyderco!

Regards,
3G
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I just want to say that I didn't bring him up to unleash any fury over the value of production knives. Obviously, he's a great artist and craftsman. But, I've heard other experts literally talk past each other (or even talk down to experience buyers and users) because they have become so set in what they do and how they do it.
 
Lucky Bob said:
Assuming that both bevels terminate at the same included angle (and why bother comparing them if they don't?), then that is factually inaccurate. I just whipped this up in a CAD program, to illustrate the point:
attachment.php


They're both 40 degree edges on a 1/8 thick piece of material. There is visibly more material inside the V-bevel shape than there is inside the convex bevel.
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Given equal stock and an equal edge angle, the convex edge has LESS metal behind it.

My thanks to Lucky Bob and to theonew
 
wow, he insults Spyderco, Benchmade, Blade-tech, Busse, BRKT, Fallkniven, Japan, Finland, Sweden, makers who don't mirror polish, and more

He insults every production knife company by stating that they don't care about quality or the customer, and that they cannot ship out a sharp knife. It's also funny how he takes shots at Japanese quality, then states that he uses ATS-34 instead of 154CM because of quality issues with 154.
 
He is right in that the vast majority of production knives will never increase in value, at least not to the extent of an actual investment medium, like a certificate of deposit or a savings bond. And, the knife market is fickle and prone to wild shifts in trendiness. But, as was said above, most is nothing more than salesmanship. He has to sell his knives, and justify the prices he charges, and factory knives are attractive and much more cost concious options. Bashing the competition is not new.
 
Having made (and tested) blades with hollow, flat and convex edges, I've come to the conclusion that a flat grind with a convex edge is the best all rounder. I've also re-ground Bucks, Schrades, Bokers, Helles and various others the same way for people and they've told me its a vast improvment.
A quick look at the type of grind used for the majority of competition blades would seem to back this up.
Whatever grind is used, its getting thicker & harder to sharpen every time.
With each consecutive sharpening, it will take more work to get the original geometry back.
But thats only my opinion, Buy whatever makes you happy:)
 
Most of my knives are convex edged, but I have only one that is a convex primary bevel. Its the CRKT Hissatsu with a continuous convex bevel from 3/4 of the blade height down to the edge. Its sharp, but not magical. It also has a 3/16" spine, which slows it down a lot. I've not been able to detect any difference in the sharpness of the edge between flat edge bevels off my Sharpmaker and convex edge bevels off my belt sander. Both test at 15-20 grams on the thread and scale set up I made. The way I see it, the majority of the improvement noticed when taking a flat ground knife to convex ground is due to thinning of the edge and, in the ones I've done, the blade as a whole, which is really the only way to turn a flat ground blade into a convex ground one. The other advantage is that the corners of the flat edge bevel are basically speed bumps, and, given equal edge angles, the convex edge has simply removed them. See the illustration above for what I mean. I read on BF somewhere that Bark River knives aims for a final edge bevel of 26 degrees (13 per side). This is remarkably thin for a factory edge, as the standard is around 20 degrees per side. I feel this accounts for much of the highly praised cutting ability of the BRKT knives. My best cutting knife as of right now is a Buck lockback reground to a flat primary grind with a convex edge put on. After the first regrinding and sharpening, it measured 0.003" behind the edge bevel. The convex edge helps, but the majority of the cutting ability comes from the very thin edge, and the sharpening angle, which is somewhere in the 10-12 per side range.
 
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