Does Anyone know how to sharpen convex edges with a stone:)

A stone is a flat surface, a convex edge is a rolled bevel. There in lies your problem.

But I guess you could slide the edge on the stone and rock your hands a lot hoping to achieve it.:rolleyes:
 
There are a few experts here who I'm sure will provide some input. If you're looking to completely re-do your convex bevel on a stone, some can do it. But it takes some skill to do it right. Most prefer to use belt grinders or sandpaper with a soft backing for that job.

For my two cents, if you're just needing to touch up the very edge, that can be done with VERY LIGHT edge-leading strokes on a stone, same as with any other knife. I use a ceramic stone to occasionally 'freshen up' the edges on some of my knives, including a few that have been convexed. In essence, you're basically putting a microbevel on the very edge. Many folks here prefer a microbevel on their convexed edges, and I believe at least a few manufacturers of convexed blades actually do it, straight from the factory.

You can also 'strop' the knife (edge-trailing strokes) using sandpaper on top of a leather hone (strop block). Very easy to make one with a scrap of wood and a piece of leather, and something like contact cement or carpet tape to stick 'em together. Lay the sandpaper on top of that. Just choose the grit based upon how much 'work' needs to be done on the edge. For general maintenance, you'd probably do just fine using something like 400 grit or maybe a little higher. If a little more refurb is needed for the edge, start with something lower, like 220 grit. Then refine it from there, with gradual steps (to 320, 400 and beyond, if you desire). I've found this method to be my favorite. It's VERY easy, if you're already comfortable with stropping on a leather hone.
 
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somber said:
A stone is a flat surface, a convex edge is a rolled bevel. There in lies your problem.

But I guess you could slide the edge on the stone and rock your hands a lot hoping to achieve it.:rolleyes:
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That's actually how I've done it.

The trick does in fact lay in raising the spine up and down as you move the knife, but using that motion to smooth out edge faces created by grinding at different angles. You grind in a very shallow (or at least shallower than the grind currently on the knife) partial V bevel, but leave some of the original bevel at the very edge so you form two shoulders. Then you slowly lower the spine as you do a edge-leading stroke, and slowly raise it while pulling back in an edge-trailing stroke, being careful not to raise the spine higher than where you originally started grinding in your V bevel, and trying to get the blade surface as flush with the stone as you can ( I used tape so i didn't scratch ). Then once you take out the two "shoulders" caused by the V grinding, you can start to lift the spine just a little bit higher than what you ground the V bevel in at to finish it up, and just match the same process on the opposite side.

I've only done it a couple of times and it requires a little bit more attention than grinding a V bevel, but I liked the edges I got doing this. They're mostly on FFG kitchen knives though, and I generally do mine in convex since it seems to do better with my housemates throwing them around in the sink on plates and such; they still cut very well even after such horrible abuse. So yeah, not a real convex aficionado, but I do it all the time on my kitchen knives. It's actually really quick to touch up once it's ground in all the way.

But, yeah, it's basically just grinding in a couple of bevels at angles that roughly match the radius you want, and then lifting the spine upward and downward to round the crests or "shoulders" that the bevels form into a smooth radius. I adopted the idea from grinding in radii into drift keys and radius gauges. I'm sure I'm not the first person that's thought of it though.
 
Im just touching up the edge and its mostly on already convex ground blades(Bark River etc).I do it with sandpaper but would like to learn to do it with a stone.
 
I've done it, several different ways. These methods are for convexed bevels, not edges.

One way I put an edge on cold chisels, and drill bits is with an upwards facing disc grinder.
All you do is lay the bevel flat, and lift the back up slightly while pulling back. Practice with a few dry runs first until you get the hang of it.

It can be done with stones too but involves more work.
The way I do it is first create the general convex shape with a file.
Pretty easy to accomplish, and once done all you need is to refine the bevel and remove scratches.

Now use the sharpie trick and color the whole bevel.
Next lay the bevel flat on the edge, and move the blade towards you with an edge forward stroke.
Rock the blade by lifting the edge so the stroke ends with the back of the bevel on the stone.
Do the reverse for the edge trailing stroke. Aim for a shallow scooping motion.

Examine the bevel and look at where you are grinding. Rock the blade where approptiate to get an even fnish. Go up to a higher grit when done.
Ignore the actual edge for now. All of this is cosmetic.

Once the bevel is fnished sharpen the actual edge like a V grind. You will end up with a very slight secondary bevel.

I know it doesn't sound like a technique that would give good results but It does.

Did this using the same method. Used a smooth file, 250 grit diamond, and soft Arkansas, and Autosol loaded strop.

DSC02525.jpg
 
in japan this is called hamaguri ba. widely used on kitchen knives.

it's not a convex like you do with sandpaper and a soft media, but the technique is to create a wide bevel at a thin angle not all the way to the edge then a bevel at the desired angle that goes to the very edge then round the trasition on .... say the two finest stones used by creating a couple other bevels. usually the wide bevel isn't polished more than 1-3k just to keep it smooth . require quite a lot of skill to do properly.
 
boki_zca said:
I was looking on youtube but everyone does it with sandpaper or belt sander.Thx
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I prefer to do what I want the easiest way, so I use sandpaper or a belt sander - why do you want to get the same results, but do it a harder way?

I set the convex bevel with a WorkSharp knife sharpener (mini belt sander that sells for $70) and then maintain the edge with a strop (green compound on leather). I also bought one of these: http://www.knivesshipfree.com/Complete-Sharpening-Kit-for-Field-or-Home-w-Black-OtterBox for field sharpening.

For the cheap way of convexing (maybe to try out a convex edge on one knife) just buy some sandpaper and put it on a soft surface (mouse pad or similar). This will be much easier than using stones and wont cost much.
 
I am toying with this style of sharpening, processes described here are what I have been practicing on flat stones/freehand. 2 questions:
1. Are there any kitchen knives that have this type of edge as a standard? I sharpened a Schun for a customer with a standard flat bevel. I ruined a set of hair stylist shears doing this, hope I didn't make the same mistake.
2. Does this style of sharpening provide any added benefit? I have heard the rounded bevel (basically what it is I believe) will push the material being cut out of the way faster (less contact with the blade) thereby reducing friction and easing the cut action.
 
Convex is actually one of the oldest edges found on items with an edge, most often in the past achieved by accident in a lot of cases and is one I learned before most other edges. The trick for me is not to over think it with a western mindset of rigid controlled linear movements. Another tip might be to move the stone on the knife instead of the knife on the stone like I observed the older folks of the old country do. They used small circular flowing motions instead of slicing motion, sort of rolling over the edge side of the blade. Give that a try and see if it works for you.

Edit to add: Funny thing is I cannot actually achieve good results using things like sandpaper belts, mousepads etc. but I can achieve a true convex that easily shaves hair with stones, just takes practice and a different mindset.
 
Yes it can be done in that manner ^. Or on the side of the stone. Round the corner first, then do it in sections. I have not determined if there is much benefit in a convex edge. DM
 
My opinion from actual hand sharpening is that a convex edge is the only edge possible without using a sharpening jig. For a true facet at the edge (non convex) a guide with a set angle is required. Part of the reason I hate hand sharpening . . . roundy edges with inaccurate geometry.

That said I will be experimenting this week end with my first convex blade. I plan to grind a Ti Lite IV to be truly thicker at the center ridge and thin out the area up at the spine. Where as from the factory the spine is still the thickest part of the blade even though there is a center ridge the length of the blade.
I will be going for something on the order of 1.9 to 2.2 mm at the center ridge and down to around 1.5 to 1.9mm at the spine. I've already full flat ground a Ti Lite IV to 1.9 at the spine and reprofiled plenty thin behind the edge. Now that's my idea of a knife. Four inches of super slicing goodness CTS-XHP of course.

The advantage for me of the blade being bulbous in the center and thinner at the spine is a blade that is wide enough to be strong yet able to cut curves better than a full flat grind.
Still though I will sharpen the very edge on the Edge Pro. ;)
 
CableGirl said:
Convex is actually one of the oldest edges found on items with an edge, most often in the past achieved by accident in a lot of cases and is one I learned before most other edges. The trick for me is not to over think it with a western mindset of rigid controlled linear movements. Another tip might be to move the stone on the knife instead of the knife on the stone like I observed the older folks of the old country do. They used small circular flowing motions instead of slicing motion, sort of rolling over the edge side of the blade. Give that a try and see if it works for you.

Edit to add: Funny thing is I cannot actually achieve good results using things like sandpaper belts, mousepads etc. but I can achieve a true convex that easily shaves hair with stones, just takes practice and a different mindset.
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My Grandfathers pocket knives always had convex edges, never knew if they were on purpose or not.. think so.
I will sure try the stone method, currently practicing on an old bread knife that will ultimately be used as a watermelon cutter (specific use blade). The test is getting thru the rind without the "pop" of a standard edge as it breaks thru the outter layer.
 
David Martin said:
Yes it can be done in that manner ^. Or on the side of the stone. Round the corner first, then do it in sections. I have not determined if there is much benefit in a convex edge. DM
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Thank you, benefit may come from the radius of the convex ( just a thought ).
 
All edges done freehand are convex,more or less.You control degree of convxivity and angle,taking the shoulders off,grinding multiple bevels and blending it in.It is easily done on stone.
 
I too, like so many others, find that old school freehand sharpening on quite small stones like they used to do it where I grew up (and probably everywhere else as well) will gradually create quite convex edges even if the starting point is a perfect "V" edge.

The technique is basically holding the stone with one hand and the knife with the other, or lay the stone on something and then sharpen just using one hand in semi-circular back and forth motions with pretty even and light pressure all through the cycle. Especially if you let your motions be a little bit loose or just "do it" (i.e. while watching TV) instead of being super focused on what you are doing and trying to be consistent, there will be enough natural play in the movements to round off things.

What might be difficult doing it this is perfectly apexing all along the edge, and getting consistent bevels on each side. Blade geometry and aproximate sharpening angle plays a huge part as well. If the end goal is a highly refined and polished edge I would not go this route, as depending on your skill, the inconsistency in the movements may or will create many uneven portions in the grind/scratch pattern and variations in the width of the bevel on each side that will become very visible at finer grits/polish. But, for a working edge, yes by all means. This is the way they often did it when the hand cranked stone wheels could not be used (needed two people) or was not available.
 
Yes,sharpening in circles and stone held in hand produces convex edge,this is how my grandfather taught me to sharpen,for utility toothy edge this is the best,although i think convex is little overhyped by some companies,it is excellent for choppers and axes,and makes big difference,but for pocket knives and slicers its more the thickness of stock and thickness behind the edge.Nevertheless all freehand edges are more or less convex.btw convex grinds and convex edges are different thing,convex grinds excell with axes ,machetes and choppers,i prefer flat or hollow grind with convex edge,also slight convex like Opinel does is pretty good,all depends on maker how they want to make it to be stronger or weaker(thinner behind edge=better slicer),and also thickness of stock.
 
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