Disadvantages to convex grind?

Free-hand sharpening tends to produce convex final bevels.

My wife inherited her GGF's carving knives and about a cubic foot of assorted sharpening stones. He was a pro brought over from Germany by Pullman Corp. to do the woodwork on custom Pullman cars - the executive jets of their day. They are simple flat-ground knives (Sloyd-looking for those who are inta' old knives.) and all have convex final bevels.
 
Thomas Linton said:
Free-hand sharpening tends to produce convex final bevels.
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Not nearly to the degree when purposefully convexing an edge. And if you keep your angle steady, with practice you can mostly eliminate accidentally hand sharpening convex bevels.
 
19-3ben said:
Thanks for the info guys!



I was actually asking because I am very very close to pulling the trigger on a KO-worksharp, and since it would convex my edges, I just wanted to double check before finalizing.

I have been working with stones first to get the basic skills, but frankly, being very pressed for time (two jobs, two dogs, wife, 17month old) the worksharp would cut down my sharpening times and pay for itself with time saved.
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Buy the ko wskt, it's an excellent machine that puts a sharp polished edge on relatively quick. I honestly prefer a convex edge, it makes the knife just glide thru material. If you're worried about convexing all your knives get the blade grinding attachment as well, with the adjustable belt tension and pulley placement you can touch up v edges with light pressure. Over time you'll gradually begin convexing the edge but will only be very slight oppose to a high ground convex the normal attachment will put on it.
 
I think they look great. Disadvantages I would say are ease of sharpening (for some folks; others say they're actually easier for them - depends on your sharpening system and skill level). And convex-ground blades typically have more steel behind the edge, and that makes them heavier than, for example, a V-grind blade. And maybe cost - I think it takes more hours and skill to properly execute a convex blade over other geometries, but I could be wrong on that. Just my 2 cents..

 
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As is often the case with these threads it is worth trying to keep the distinction between a convex primary grind and a convex secondary edge bevel (and combinations of the two with themselves and others.....!).

On topic, been shaprening and reprofiling all my knives to a convex secondary edge bevel with no ill effects yet:) As with any freehand sharpening method it requires practice and you can balls it up!:)
 
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avoidspam said:
As is often the case with these threads it is worth trying to keep the distinction between a convex primary grind and a convex secondary edge bevel (and combinations of the two with themselves and others.....!).
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That would make too much sense!
 
I think that on a big knife, the convex edge gives good cutting ability and decent slicing ability. To me it is also the easiest to sharpen. For the best slicing though I think a straight V edge can be taken down low and offer better slicing ability. HEre is a factory convex edge on a flat ground profile. The convexing starts 3/8 to 1/2" from the edge.

bolo2.jpg
 
These discussions keep coming up over and over, mostly because people think there is something magic about convex edges. There is not.

A convex edge and a V edge can be so nearly identical that you could tell one from the other only with a scanning electron microscope.

A convex edge can have more or less steel behind the edge than a V edge.

A convex edge can be more or less acute than a V edge.

The real disadvantage of a convex edge is that you don't know what you have. There is no good way to easily and precisely measure their acuity as there is with a V edge.

But if you compare edges with the same three boundary points (the apex and both shoulders), a V edge will be more acute and a convex edge will be more robust. How much more acute and how much more robust depends on the specific geometry of the edges in question. There may be huge differences, and there may be virtually no differences.
 
In my experience, MY convex grinds aren't good for wood feathering.

But nearly all my chef knives are convex due to long lasting edge.
 
craytab said:
Not nearly to the degree when purposefully convexing an edge. And if you keep your angle steady, with practice you can mostly eliminate accidentally hand sharpening convex bevels.
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A top level professional carver sharpens his knives to what works for him by accident? Poor man. What might he have accomplished "with practice" over the sixty years of his career?
 
DeadboxHero said:
Curls fo days.

My favorite


Effort to sharpen

Least favorite

But the
Results

Gorgeous
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Nice work!
Im thinking it's my skills that are lacking.

I'm probably better at convex on kitchen knives than wood working. Here's what my convex usually looks like.
 
Thomas Linton said:
A top level professional carver sharpens his knives to what works for him by accident? Poor man. What might he have accomplished "with practice" over the sixty years of his career?
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Don't know what the hell you're exactly talking about but in my over 1 million years of sharpening experience, I can safely tell people they certainly can learn how to freehand sharpen a consistent angle. Not exactly rocket science :thumbup:
 
Thinly ground full convexed edges work best for a general utility blade IME. The knife glides through material and has a more robust tip for rougher media. Second best is a thinly ground primary grind with a thin convexed edge. Some grinds are better at this or that but for general use convexed is how I lean.
 
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A convex EDGE "grind" is sexy and perhaps helpful if the primary grind's thickness is thin behind the edge! It's a primary grind that I don't like the look of. Plus in my typical size knives (3-4" blade) they are completely unnecessary.
 
hermit dave said:
A full convex blade grind like the SM III Trail Master and Recon Scout mimics a more acute
edge angle and reduces friction even further. This is why the mentioned knives cut like magic.
The downside is a more fragile edge.

.
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I have bought a few months ago a brand-new Cold Steel San Mai III Trailmaster, specifically for the purpose of comparing chopping performance to my other knives. The original edge was flawless and razor sharp, and it cut wood like absolute crap. It was out-chopped, at 17 ounces and 9.5", by an 11 ounces Al Mar "Special Warfare" that was 7.75" long, and which had a correct hollow grind with a 0.020" V-edge... Not out-chopped by much but still...

The Trailmaster started to cut a little better when I carved a deep V-edge into its way too fat convex, but it never got beyond about 2/3rds of the performance of my Randall Model 12, which means around half the performance of my Lile Mission...:

P9076463_zpssywvejni.jpg


The Trailmaster blade felt quite blade-heavy just from the convex swelling, which is why the Lile "Mission is actually lighter than the Trailmaster by a fraction of an ounce(!)... Since the "Mission" has a correct true flat grind, it still outperforms by a huge margin a knife that weights the same and looks far smaller... How is that supposed to translate into "magical" cutting performance completely confounds me, but what do I know?

As far as low energy slicing is concerned, to even consider that convex has anything to offer over a thin V-edge is quite extraordinary, and was never a claim of Moran and other early proponents of convex edges (in the 1970s)...: Moran explicitly designed convex edges for chopping and other high-energy contests, hanging manila rope being a big fixtures in those days (one can see how a full convex might help for that)... Few of today's convex edges proponents even seem to remember they used to be called "Moran edges"... This means that, in those days, none of the ancient blades, outside of axes, were thought to be that way through an intended design, instead of a byproduct of the available sharpening/finishing method... Maybe convex edges can make wood curls better but that is about it, slicing wise...

Gaston
 
Twindog said:
These discussions keep coming up over and over, mostly because people think there is something magic about convex edges. There is not.

A convex edge and a V edge can be so nearly identical that you could tell one from the other only with a scanning electron microscope.

A convex edge can have more or less steel behind the edge than a V edge.

A convex edge can be more or less acute than a V edge.

The real disadvantage of a convex edge is that you don't know what you have. There is no good way to easily and precisely measure their acuity as there is with a V edge.

But if you compare edges with the same three boundary points (the apex and both shoulders), a V edge will be more acute and a convex edge will be more robust. How much more acute and how much more robust depends on the specific geometry of the edges in question. There may be huge differences, and there may be virtually no differences.
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^ I support this post :thumbup:

Also, if "convex" encourages people to thin the shoulders of their knives into a more efficient cutting geometry than what was there before :thumbup: Thinner cuts better so long as you don't compromise the strength/durability of your blade.
 
Comparisons of grind types usually degenerate into arguments and attempts at technical explanations with some percentage of the participants not understanding what the opponents are saying. The lesson to learn is to not invite arguments about different types of edges.

I think a person can do an ugly job of any grind type. Most of my knives are V grinds but some of the sharpest I have received were some form of convex. I'm not sure I really care one way or the other.

I have a guided sharpening system with diamond stones so it is far easier for me to sharpen a V edge, even a dull one with super steel, to a V edge on my guided system than it is for me to sharpen a convex. I've tried the sandpaper+mousepad trick several times and it just didn't work. I might have not spent enough time on it but I spent more time than it would have taken my diamond stones to sharpen a very dull edge on very hard steel. I have a couple of Bark Rivers with sharp convex grinds. I don't know what I'll do when they get dull but at least I'll try the sandpaper trick again because that's what they tell me to do.
 
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