Convex grind on very thin blades

[nuggetz]

Tonight I made a real honest attempt at convexing a new knife I picked up - an Opinel #6. I used wet/dry sandpaper on a mousepad method. Well actually, my 8K Shapton Pro stone came with a nice piece of protective foam which I used instead of a mouse pad. I started things off at 400 grit and used very light pressure with edge trailing strokes. I made a point not to go past 400 grit until I absolutely felt the burr on both sides a couple of times. Anyway, I progressed up to 2000 grit using wet dry and then all the way up to 12K using micromesh sandpaper and was pretty happy with the results but not ecstatic. Gave the blade a good stropping and I can slice paper easily and shave hair.

As this was my first honest attempt at producing a convex edge I started to question whether or not it was worth the hassle since the blade is so darn thin that it would probably slice anything in the kitchen even with a utility edge. Also, since I opted for the Opinel #6 with a walnut handle, the only steel that was available in that configuration was stainless. My Opinel #8 is carbon and I would have loved it if Opinel made a #6 carbon with walnut handles. Anyways, I feel the edge could be better but I'm wondering if I'm butting up against the limit of attainable sharpness for stainless. In any case I'm questioning my convex sharpening skills. At the higher grit levels I honestly couldn't tell if I was producing an even burr. So I counted strokes and made sure I spent a good amount of time on each side before doing the other side and then moving onto the next grit. Can anyone chime in with any tips? I started with the blade flat against the sandpaper and then used edge trailing strokes and lifted up until I felt a bit of resistance. Logic tells me that the resistance is the edge of the knife hitting the sandpaper so I have a question. Should my stroke be lowered so that it feels smooth with absolutly no feeling of resistance from the edge or should the "feel" include some resistance?

Convex sharpening always seemed difficult since you are using a surface with some flex and I have a hard time imagining how a sharp non-rounded edge was even possible when compared to sharpening a knife on a hard flat surface where the bevel is in constant contact with the abrasive. Am I looking at this logically?


Here's the knife. Pic isn't the best as the front of the knife looks like it wasn't honed correctly but it is truly convex along the entire length.

 

[duxbellorum]

Looks very nice!

Although it is very hard to do on a knife with a curving tip, traditional convex bevels are ground on hard stones by tilting the knife during each stroke. Using that method, you can carefully control the angle tangent to the edge and get it very nicely apexed. The mouse pad method introduces a separate variable: pressure. pressing down harder increases the flex of the pad, increasing the roundness of your grind. I personally think it's easier to figure things out on a hard/flat stone than on a flexible pad.

On the stone if you are over-tilting the knife, the edge makes a rasping sound that tells you are taking metal off of a thin surface. I think that's the roughness you feel on your sandpaper.

As you are sharpening, you want to keep things smooth, but get as close to the edge as you can. Use the sound or the rough feeling to figure out when to stop tilting. You should be grinding close enough that you are right on the edge (no pun intended) of feeling that rough sensation.

Like all sharpening, experience is your friend, and if you have a cheap knife to play around with, try putting a convex edge on that one. Especially at the lower grits -- when the bur is easy to identify -- you can refine your tilting technique. The motion that works for low grits should also work for high grits, so all you will have to do after that is maintain consistent technique.

 

[awestib]

I thought Opinels are convex anyway?

 

[Obsessed with Edges]

Just 'strop' the blade on some medium/high-grit wet/dry sandpaper over a hard backing, like glass or stone. That's really all that's needed to produce a gently-convexed and very sharp, crisp edge on an Opinel blade. Most of the troubles in over-rounding the apex come from sharpening on a softish backing, like leather or a mouse pad, and more troubles are created in deliberately rolling the wrist/hand during the stroke. A natural, freehand stropping motion will vary a little bit in angle anyway, and a convex will always result from any freehand honing.

The other troublemaker is in trying to make too much of a convex; it may look nice, but the edge will be sharper with an apex that still essentially forms a 'V'. Any advantages of the Opinel's convex are due to it being behind the apex (primary grind), and not immediately adjacent to it. Focus on thinning the edge itself, and keep any rolling or deliberate convexing behind the edge. That'll produce the best results.


David

 

[HeavyHanded]

That's the ticket, do not rely on the density of some backing material to determine the amount of convexity of your edge. One can easily (with a small amount of practice) create a convex edge even on a diamond plate, and so control the shape of the convex to pretty tight tolerance to the curve you want. Cosmetically it takes some doing to have it look nice-nice without loaded stropping, but it can be done without too much trouble. Be realistic.

A slight roll of the wrist as it moves across the abrasive surface is all that is needed. As the edge on a convex approaches the apex it (to me) has an even more pronounced feeling of apex catching than many V bevels. I 100% agree with OWE and have for many posts of this nature - it cannot be emphasized enough - the final bevel should in essence be a V bevel with a convex curve leading into it. On really thin stock flat primary ground edges it is bit of overkill to do a conversion - cutting will be enhanced only a small bit and might not even be noticed - but if carefully managed will still yield an improvement. This will be lost if the terminal apex becomes large.

Keep in mind especially with thin stocked tools, if you use it hard, leave it as a V bevel. All other things being equal, converting a V bevel to a convex at the same terminal apex angle will always leave it more susceptible to lateral stresses.

 

[lonestar1979]

Its so easy to sharpen these, don't worry about convex etc, just do not make too high of an angle! In my opinion convex is overrated, besides the choppers!On these smaller blades you do not have to worry on transition between convex and v edge its all similar, so you can use ceramics, sandpaper, stones, almost anything.\this is a thin blade and an excellent cutter.Overrounding of the apex is the problem, that's where most pple make mistake.Get some flat stones and lower the angle, its gonna be convex anyways.

 

[AFAustin]

I 100% agree with OWE and have for many posts of this nature - it cannot be emphasized enough - the final bevel should in essence be a V bevel with a convex curve leading into it.

You gents have educated me on this point and it's been a valuable lesson---smooth the shoulders and "v" the apex.

I typically do an initial sharpening with my Work Sharp KO, which produces a shallow convex and nice round shoulders. Doing a full belt progression yields a nice edge as well. But by finishing off on the Sharpmaker, especially the UF stones (and a few strokes on a denim-on-wood strop with compound), the edge becomes even better. This followed by regular maintenance on the Sharpmaker and strops.

To the OP: I wouldn't worry about having the Opinel stainless as opposed to the carbone. In my experience at least, the Opie stainless takes a wonderful edge.

Andrew

 

[Obsessed with Edges]

You gents have educated me on this point and it's been a valuable lesson---smooth the shoulders and "v" the apex.

I typically do an initial sharpening with my Work Sharp KO, which produces a shallow convex and nice round shoulders. Doing a full belt progression yields a nice edge as well. But by finishing off on the Sharpmaker, especially the UF stones (and a few strokes on a denim-on-wood strop with compound), the edge becomes even better. This followed by regular maintenance on the Sharpmaker and strops.

To the OP: I wouldn't worry about having the Opinel stainless as opposed to the carbone. In my experience at least, the Opie stainless takes a wonderful edge.
Andrew

+1 to that. :thumbup:

I've been continually experimenting & tinkering with my stainless Opinel (No. 08 in walnut). I bought it in tandem with a No. 08 'Carbone', and immediately thinned both blades to a zero-grind (no secondary bevel at the edge), using wet/dry paper over glass, up through 2000-grit; also followed with some additional polishing, so both blades are essentially mirrored now, at least in the lower 2/3 of the blade's width. Since doing that, I've continued to tweak my own methods in touching up the edges on both of them; results have always gotten better with a harder/firmer touch-up method, whether it's sandpaper-over-glass/stone, or a ceramic hone, or a diamond hone. I've always followed with stropping on denim with some white rouge; this maintains the polish pretty well, and is still the best remedy for burrs I've seen.

In doing all that tinkering, I'm continually impressed with just how fine & sharp an edge the stainless (12C27Mod) will take, as compared to the 'Carbone' (XC90) steel. Both get equally fine (thin), but the stainless will hold a thin edge longer, and it still retains an amazing 'bite' in cutting that seems otherwise 'invisible' when just feeling the edge with the fingertips. At similar thin geometry, the 'Carbone' blade still cuts very well, but is more delicate and vulnerable to rolling or denting with light impacts at the edge. The stainless blade has been more durable, at similar cutting geometry.


David