# Convex Edges



## MadMel (Sep 14, 2011)

As the title says, this is about convex edges. I have heard that it prevents food from sticking to your blade but how exactly do you achieve a convex edge when sharpening? Now I can sharpen well enough and do so often enough to say that I can get my edges shaving sharp but it kinda bugs me when food sticks to my knife.


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## stevenStefano (Sep 14, 2011)

In my experience, I got a nice convex edge by thinning my JCK KV8, I made a thread about it. That was my first time and it worked out better than I could possibly have hoped, that was over a month ago and the knife it still very sharp and cuts very well. I'd say it almost cuts better than all my more expensive knives. As you say, it means very little sticks to the blade, just like Salty's video. If you wanna do it less radically, perhaps just sharpen further up the blade a little and kinda rotate it intentionally? Here is a thread at FF which might help you


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## Lefty (Sep 14, 2011)

Here we go again.... :shocked3:


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## Eamon Burke (Sep 14, 2011)

A convex edge bevel won't keep food from sticking. This is addressed by a convex bevel on the face of the blade, and is a lot larger. It's a bit of a debated topic, but it's been shown to work, at least to some extent.

Convexity in an edge bevel is attainable 2 ways--either by sharpening on a soft-backed abrasive, or....by sharpening by hand. All hand sharpening produces a tiny amount of convexity on the edge bevels. You can get a dead-flat bevel on the edge by using a jig, but a flat bevel provides no advantage. Neither edge bevel helps with food sticking.


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## NO ChoP! (Sep 14, 2011)

But, a convex edge does help with edge retention, right? Since there is more metal behind the point of the edge, I would assume.


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## tk59 (Sep 14, 2011)

NO ChoP! said:


> But, a convex edge does help with edge retention, right? Since there is more metal behind the point of the edge, I would assume.


 To some extent depending on the type of damage your edge tends to take. If the damage is mainly due to wear, a convex edge will dull faster. If the damage is due to deformation or cracking/chipping, it will certainly help. As for sticking, Eamon has it right. Release is due to a curvature in the face of the blade. More curvature = less sticking BUT it also = thicker blade or more asymmetric. You can't have your cake and eat it, too. Or was it, "There's not such thing as a free lunch."?


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## memorael (Sep 15, 2011)

You can convex edges too by applying different pressure on parts of the blade my man, think of it as bending the knife a bit and also by wiggling the knife at the same time. I find the best way to do this without messing your cutting edge up is making a strong hefty bevel and then thinning it out while you convex the blade. This is really hard to make on a laser so A types and heftier blades that come unsharpened work best since you have more metal to manipulate.


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## olpappy (Sep 15, 2011)

Ya, I agree with that last part, if you have a thick bladed knife the easiest way to get it sharp without having to remove a lot of metal is by convexing it.


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## stevenStefano (Sep 15, 2011)

Yeah I agree with you memorael about it being easier with thicker blades. I'm gonna thin my Hattori FH some time soon whenever I stop being lazy. On my KV8 I think I went a bit further than I had planned but the performance increase was huge, there is no visible bevel on it now, it is totally blended into the face


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## JohnnyChance (Sep 15, 2011)

[video=youtube;UdEe9sEQRcE]http://www.youtube.com/watch?v=UdEe9sEQRcE&feature=player_detailpage[/video]


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## JBroida (Sep 15, 2011)

i saw rockbox post that video yesterday... very good video


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## Dave Martell (Sep 15, 2011)

That's one of Murray's better videos. I particularly liked the point he kept making of observation - look at the blade while working. This is such a simple thing that is so critical to getting done what you want to get done.


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## Lefty (Sep 15, 2011)

The top three sharpeners seem to agree on this one!
I'll follow the advice for sure, now!


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## JBroida (Sep 15, 2011)

Dave Martell said:


> I particularly liked the point he kept making of observation - look at the blade while working. This is such a simple thing that is so critical to getting done what you want to get done.


 
+1


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## memorael (Sep 15, 2011)

Some of my knives have no visible bevels and these are usually the ones that perform like lasers. Convex bevels depending on how pronounced the convexity is will help with the food sticking problem. They are also fun to make, making sure all the scratches are in the same pattern and stuff.


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## jmforge (Sep 16, 2011)

You can convex a blade too much, especially if you try to grind it on a slack belt. I do it on a KMG rotary platen and still end up "flattening" it a bit when hand sanding.


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## JohnnyChance (Sep 16, 2011)

******* said:


> You can convex a blade too much, especially if you try to grind it on a slack belt. I do it on a KMG rotary platen and still end up "flattening" it a bit when hand sanding.


 
And what happens when you convex it "too much"?


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## tk59 (Sep 16, 2011)

Yeah, I'm not sure why you'd put slack in your belt anyway. There's usually enough give on mine if I just move the platen back a bit. I suppose with enough slack, your knife would just be very thick behind the edge. In that case, it seems like you wouldn't want to flatten, you'd want to thin behind the edge is all.


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## MadMel (Sep 18, 2011)

Hmm so it does not help too much with the food sticking problem then. But basically, what are the pros and cons of it? I've read through the posts and it seems that mostly it is down to thinning and personal preference?


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## stevenStefano (Sep 18, 2011)

MadMel said:


> Hmm so it does not help too much with the food sticking problem then. But basically, what are the pros and cons of it? I've read through the posts and it seems that mostly it is down to thinning and personal preference?



Well no. It helps massively in terms of food sticking in my experience. My KV8 I thinned cuts potatoes better than any other knife I have, potatoes and pretty much everything just falls off the blade. A pretty big advantage. I'm gonna thin and convex my Hattori FH some time this week hopefully so then I can experiment a little more


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## obtuse (Sep 18, 2011)

I just thinned and convexed the right side of my Suisin HC gyuto. I convexed from about midway up the blade to the edge and finished with a micro bevel. Only diced a bunch of onions so far, it fell through them with little effort. When I get better at the technique, my Akifusa will have a date with the stones. Thanks for posting that Carter video!


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## Dave Martell (Sep 18, 2011)

MadMel said:


> Hmm so it does not help too much with the food sticking problem then. But basically, what are the pros and cons of it? I've read through the posts and it seems that mostly it is down to thinning and personal preference?




The edge and blade face should be thought of differently. If you convex the edge of a thin kitchen knife then the performance drops because the edge thickens and becomes a wedge but if you convex the blade face the performance goes up from less wedging and surface sticking.


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## Eamon Burke (Sep 18, 2011)

tk59 said:


> Yeah, I'm not sure why you'd put slack in your belt anyway. There's usually enough give on mine if I just move the platen back a bit. I suppose with enough slack, your knife would just be very thick behind the edge. In that case, it seems like you wouldn't want to flatten, you'd want to thin behind the edge is all.


 
Slack belting is just using the belt without a platen holding it in place. So if you move your platen back, you're slackbelting.

Murray doesn't do a lot of bevel grinding on a belt grinder, he has a gigantor water wheel, so his methods are more rustic. You can totally convex a blade face by cutting in a few careful bevels on a platen, and GENTLY slackbelting it...you do have to be careful, you can overgrind the edge portion very quickly like this(not that you can't on a 1k stone).


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## shankster (Sep 19, 2011)

Noob question..Is a convex edge well suited for all blade types(gyuto,santoku,honesuki,boner etc)?

PK


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## Eamon Burke (Sep 19, 2011)

No. Nothing is well-suited for every blade type, except even grinding and good heat treat.


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## G-rat (Sep 19, 2011)

I think this has got to be one of the most helpful sharpening videos I have ever viewed, and of course especially as it pertains to convex sharpening. There is one other I found which was very helpful but the man spoke very poor english. His sharpening skills were awesome and I got the general idea but seeing this with clearer english, my problem not the japanese man's problem, and with the drawings is massively helpful. I am doing this right now with my moritaka cleaver. The one disadvantage I see happening over time...like years and years of sharpening...is that eventually I am going to wear into the kuro-uchi finish to keep convexing the edge, and really have trouble with oxidizing food. Luckily I have found that Moritakas iron will take an ok patina simply through use, cleaning and allowing it to sit out in the air and not covering it up or putting it into a paper saya. Thanks for posting this video johnnychance. It has taken hours and hours of sharpening. I would have loved to have posted a WIP progress type post with pictures so that others could learn from my mistakes and hopefully my sort of ok execution with this as I had lots of trouble finding anyting on the internet that explained it as clearly as this video did.


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## chefofthefuture (Sep 19, 2011)

G-rat said:


> The one disadvantage I see happening over time...like years and years of sharpening...is that eventually I am going to wear into the kuro-uchi finish to keep convexing the edge, and really have trouble with oxidizing food.


 
That's probably the one big disadvantage with any clad knife, you're basically stuck sharpening the primary edge bevel and can only really thin the knife a few times. You can understand why many people on this forum prefer mono-steel or unclad knives.


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## G-rat (Sep 19, 2011)

Right makes sense. Maybe I should have gotten the masamoto Gyuto instead of the mizuno...I guess time will tell in a pro environment how long that $370 lasts!!


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## Citizen Snips (Sep 21, 2011)

g-rat - dont worry, ive had that hiromoto for years and you know how often i sharpen. its getting to the point where it doesn't have much life left unless i thin it out. im not planning on thinning it as my wife is going for her first wa-handled carbon knives (im very nervous and excited for her) so we will probably just use it as our home knife and give the 5stars to my brother in law. back on track, i wouldn't worry about it. it will be a great cutter and although it will take some time and patience a few years down the road, you can thin it and keep it going. for that knife, you can spend the time on it but for something like the hiro if i wanted to keep using it, i would just buy a new one


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