I really dislike convex sharpening...

[ShooterMcgavin]

Am I alone or am I doing something wrong?...
I have been working on convexing my Benchmade Griptilian (154CM) and it is just taking forever. The longer I work at it, it seems the slower it goes. I think the sandpaper gets a little coated with steel dust and it stops working well. I have started with 220 grit and then gone to 400 grit and, honestly, I think I need to go back to 220 or even lower (Is that what I need to do?). I'm not hitting the edge for most of the blade and I don't want to add pressure to try to get faster results.

I have convexed a Svord Peasant and that came out "ok". It still took a very long time and I still wasn't hitting the edge for the whole length.

Frustrated.

 

[Obsessed with Edges]

What backing are you using under the sandpaper? The hardness/firmness of the backing will make a big difference in how aggressively the sandpaper works. If the backing is real soft, like a mousepad, it's much more difficult for the abrasive to dig into the steel, and grinding is much slower. Paper that's just laying loosely atop a soft backing will move too much, and that slows the grinding. A soft backing almosts screams for the user to dig harder with more pressure, in order to speed things up. But that's the worst thing you can do, increasing pressure on a soft backing; it inevitably will round over the apex of the edge.

Using a harder backing poses less risk of rounding off the apex, and that's probably the biggest advantage to using a firmer backing. If the sandpaper is glued or otherwise firmly attached to the backing, that makes a significant improvement in aggressiveness also.

I've been 'stropping' (in essence) my blades on sandpaper over glass, attached with temporary adhesive, and the feel and performance of the abrasive is very similar to using a silicon carbide stone. It even sounds very similar. Works much faster and leaves a very crisp edge as well. Interestingly enough, burring is less of a problem, and whatever burrs may be left clean up much more easily.


David

 

[ShooterMcgavin]

Thanks. I am using a mouse pad as my backing, on top of ply-wood as a base. You are right, it is because of the soft mouse pad that I fear putting any real downward pressure on the knife which would roll the sandpaper up and round off the edge. I will try with a firmer surface and a little more pressure. I thought the idea of convexing was to use a soft backing surface to get the rounded "shoulder". If we use a firmer surface, the edge doesn't turn out to be quick as convexed, right?

 

[pwet]

thickish leather with a bit more pressure will yield a very similar amount of curve. it'll be faster and more controlled imho. another advantage is that you use the same media with the same amount of give when grinding and when stropping, easier to adapt.

 

[ShooterMcgavin]

Ok. I will try it with leather backing the sandpaper. That should work much better.

 

[Obsessed with Edges]

Thanks. I am using a mouse pad as my backing, on top of ply-wood as a base. You are right, it is because of the soft mouse pad that I fear putting any real downward pressure on the knife which would roll the sandpaper up and round off the edge. I will try with a firmer surface and a little more pressure. I thought the idea of convexing was to use a soft backing surface to get the rounded "shoulder". If we use a firmer surface, the edge doesn't turn out to be quick as convexed, right?

The natural variation in your hand's ability to hold the angle in freehand sharpening is really all you need, to make a convex edge. A thicker or more severe-looking convex really doesn't add much advantage, if any. Only results in a broader (thicker) edge angle, which never cuts as well. The downside of going too soft with the backing is that it not only rounds the 'shoulder' of the bevel, but also the edge itself.

It may take some time to get used to convexing on a harder surface; it doesn't 'feel' as forgiving and can be a little more intimidating initially. But the results are worth taking the time to train your hands to it. I've gone through a progression over some time, using relatively thick leather initially, then gradually thinning the leather backing under the paper. When I'd gone as far as I could with that, I started using a few layers of paper as the backing under the sandpaper, and then decreasing the number of sheets over time. That's how I eventually ended up where I am now, just using the sandpaper directly over glass (glued). The results have steadily improved as my backing has firmed up, and I've never looked back.


David

 

[Razorsharp-Travis]

i dont see the point in convex when I can do a flat edge faster than I can reprofile into a convex, then just microbevel it to get the same apex angle as a convex. ANd when I want to touch up, I dont have to do the whole edge bevel again, just re apex the micro

 

[HeavyHanded]

Am I alone or am I doing something wrong?...
I have been working on convexing my Benchmade Griptilian (154CM) and it is just taking forever. The longer I work at it, it seems the slower it goes. I think the sandpaper gets a little coated with steel dust and it stops working well. I have started with 220 grit and then gone to 400 grit and, honestly, I think I need to go back to 220 or even lower (Is that what I need to do?). I'm not hitting the edge for most of the blade and I don't want to add pressure to try to get faster results.

I have convexed a Svord Peasant and that came out "ok". It still took a very long time and I still wasn't hitting the edge for the whole length.

Frustrated.

The sandpaper will load up frequently and need to be cleaned off or grinding will slow considerably. More of a concern when you first do a conversion than when maintaining an already convexed edge. FWIW you can create and maintain them just as well on a hard stone, and have complete control over the terminal apex angle as well as the shape of the convex arc. Takes out any trial and error with different density backings. Finished bevel face might look a little segmented cosmetically, but can be easily smoothed out with a few passes on a loaded strop. With practice a smooth finish can be done straight off the stone, though this does take practice.
Using sandpaper over * it can take a long time to grind a V bevel into a healthy convex. Subsequent touchups you simply grind the entire bevel face, concentrating on the region just above the cutting edge and lightly blending it into the apex. About half my knives are convex, I haven't used sandpaper to convert or maintain any of them for a few years now.

A crepe rubber block works very well for clearing the swarf from your sandpaper should you go that route - really pays to wipe off the paper often.

 

[Obsessed with Edges]

Most of my convexed edges have gotten that way simply in the course of regular maintenance, by stropping on medium/fine sandpaper (320 and up), instead of going through the somewhat arduous task of trying to do it all at once. It's much easier to do it this way, if the existing V-bevel is already fairly acute (30° inclusive or less) and well-formed (symmetrical). With new knives, or with others that need re-bevelling anyway, I've usually thinned them out on hard hones, sometimes using a guided setup (Lansky, Aligner, etc.).

Once the new bevels are set, and the edge is fully apexed and sharp, all subsequent touch-ups take place on the sandpaper with edge-trailing strokes, and the convex will take shape on it's own, in due course. For me, that's a much easier way to get it done, AND it's also why I frequently say stropping on sandpaper is my favorite method for maintaining my edges. It duplicates exactly the stropping stroke. So, from beginning to end, my hands are trained to do the right thing. Almost intuitive sharpening, that way; muscle memory does almost all of it.

Setting the original bevels on stones almost completely eliminates the need for reshaping them on coarse or xtra-coarse sandpaper, which will greatly minimize the issues of the paper loading up. Maintenance touch-ups on the medium & higher grits only take a minimal number of passes, as with stropping, so the loading issue isn't really a factor from then on.


David

 

[darkangel55555]

I convex on bench stones by sharpening in circles. The larger the circles, the more pronounced the convex.

Consistency is reasonable, but the body of the edge doesn't always look great. The apex works, which is all I care about for those blades I convex.

Hope this helps!

 

[awestib]

What backing are you using under the sandpaper? The hardness/firmness of the backing will make a big difference in how aggressively the sandpaper works. If the backing is real soft, like a mousepad, it's much more difficult for the abrasive to dig into the steel, and grinding is much slower. Paper that's just laying loosely atop a soft backing will move too much, and that slows the grinding. A soft backing almosts screams for the user to dig harder with more pressure, in order to speed things up. But that's the worst thing you can do, increasing pressure on a soft backing; it inevitably will round over the apex of the edge.

Using a harder backing poses less risk of rounding off the apex, and that's probably the biggest advantage to using a firmer backing. If the sandpaper is glued or otherwise firmly attached to the backing, that makes a significant improvement in aggressiveness also.

I've been 'stropping' (in essence) my blades on sandpaper over glass, attached with temporary adhesive, and the feel and performance of the abrasive is very similar to using a silicon carbide stone. It even sounds very similar. Works much faster and leaves a very crisp edge as well. Interestingly enough, burring is less of a problem, and whatever burrs may be left clean up much more easily.


David

David, what kind of adhesive do you use? Sorry if we have talked about this already!

Shooter Mcgaven, for what it's worth, I noticed that if I sharpen my scandi knives on a stone and try not too hard to stay real flat but rather let my hands/wrist move their natural way (strokes towards me tend to lift the spine somewhat, strokes away from me do the opposite), I create a nice and even convex bevel, the curve however is minimal. It is very easy to see however since it is such a wide bevel. I imagine that if I did this same motion while reprofiling a too thick edge for instance, I would create the same convexity.

 

[Twindog]

Convexing is freehanding. It's an art. And with any art, some people are going to be very good at convexing and others not so much.

If you were to examine the edge profiles of 10 convex edges done by 10 different, but experienced people, those edge profiles would likely be quite different. The angles would be different, and the edges would perform differently.

Over time, you can build up muscle memory, but it may be muscle memory for a convex edge that doesn't perform all that well.

Some people can put on a great convex edge and do it easily, but getting to that point is not something most people are going to achieve. The advantage of a V edge with a guided system is that you get exactly the edge you want. If you want better performance, you can make the V a little more acute and see how the edge holds up to your normal cutting. Or you can add a microbevel to add strength and make sharpening faster and easier.

I prefer a V edge for its easy-to-duplicate precision and my ability to tweak the edge in small, easily replicable ways so I can match steel characteristics and edge geometry to the demands I put on a knife.

Nonetheless, I'm beginning to think that the edge of a really well done, acute convex edge lasts longer than a similar V edge, but the convex edge is much more difficult to get right and easy to get wrong.

 

[Obsessed with Edges]

David, what kind of adhesive do you use? Sorry if we have talked about this already!
(...)

Andy, It's called 'DAP Weldwood Multipurpose Spray Adhesive'. Among it's other uses, it's marketed to woodworkers for attaching templates to projects to be cut, and I picked it up at a Woodcraft outlet. I spray the backside of the paper with it, then wait a few minutes for it to become dry to the touch but tacky, and then press it onto the glass. Works pretty darn well and peels off pretty cleanly later on, when it's time to change grits or replace a worn-out sheet. This is another reason I like the glass, BTW, because it's much easier to clean it up with isopropyl alcohol, Windex or whatever else you might use.

David

 

[Obsessed with Edges]

Convexing is freehanding. It's an art. And with any art, some people are going to be very good at convexing and others not so much.

If you were to examine the edge profiles of 10 convex edges done by 10 different, but experienced people, those edge profiles would likely be quite different. The angles would be different, and the edges would perform differently.

Over time, you can build up muscle memory, but it may be muscle memory for a convex edge that doesn't perform all that well.

Some people can put on a great convex edge and do it easily, but getting to that point is not something most people are going to achieve. The advantage of a V edge with a guided system is that you get exactly the edge you want. If you want better performance, you can make the V a little more acute and see how the edge holds up to your normal cutting. Or you can add a microbevel to add strength and make sharpening faster and easier.

I prefer a V edge for its easy-to-duplicate precision and my ability to tweak the edge in small, easily replicable ways so I can match steel characteristics and edge geometry to the demands I put on a knife.

Nonetheless, I'm beginning to think that the edge of a really well done, acute convex edge lasts longer than a similar V edge, but the convex edge is much more difficult to get right and easy to get wrong.

This is why I advocate duplicating a fundamentally good stropping stroke (practice to master that) on firm or hard materials. If one gets a good handle on stropping technique, and then adapts it to gradually-firmer-to-hard backing (like hardwood or glass), the rest will almost take care of itself. For me, convexing became much, much easier as I transitioned to 'stropping' on hard-backed sandpaper. Much easier to protect and maintain acute, crisp edges this way. The softish backing used by so many people for convexing is what (in my opinion) creates most of the problems and frustration, in producing thick and roundish edges that don't cut well.


David

 

[Twindog]

Hey David:

From reading your many, many excellent posts, I'd guess that your convex edges are as sharp as my V edges and last longer. A really good convex edge is a thing of beauty. Not many people can duplicate your ability.

It's true that with lots of practice and a consistent stropping stroke, someone can build up muscle memory to replicate the edge that that combination of angle and pressure produces. But what kind of edge will that be? Acute? Obtuse? Will muscle memory be the same when you flip the knife to do the opposite side? Practice makes permanent, not perfect. (My old gym teacher used to say that.) And can anyone really avoid all the slight changes in angle -- a degree or two here and there -- that freehanding produces?

I live in a small cabin way out in the rainforest. I built it myself. In the beginning, I had no power and used only hand tools. My early efforts were poor, but as I built up my skill, my carpentry became very good. Then I added solar power and could use power tools. The power tools allowed me to build much faster and improve my quality. Making tight, perfect joints with a chop saw (basically a jig, like a guided sharpening system) was a breeze. Not as easy when I had to cut everything with a handsaw, especially 4x and 6x timbers.

I think convexing is like that. With practice, convexing will get much better, but it takes a lot of practice and not everyone will master the craft, even with practice. A guided V system is much easier to master and will produce excellent results.


Hard backing for the convexing process has a lot of advantages, but a softer backing is more forgiving. Hard backing will work better for you and others who have mastered the convex edge, but be more difficult for beginners because it amplifies the user's level of skill or lack of skill.

Stropping a V edge is kind of a compromise between the guided V edge and the freehand convexing. It's not easy to learn. Lots of people try, but can't make it work. For others, it really improves their final edge. Stropping can work in two ways: it can refine a V edge, especially with hard backing or light pressure, removing any burr and perfecting the apex; or it can create a micro convex edge at the apex of the V edge, making the V edge stronger and last longer. The hard part is knowing exactly which approach you're using because it's not easy to see what's happening to the edge at that scale.

Hard back stropping works better to refine a V edge, but softer backing works better for producing a micro convex apex.

 

[Obsessed with Edges]

A 'micro convex apex' is what I try to avoid, at all costs. There's no advantage to convexing any part of the apex. The best 'convex', as I see it, is one that convexes the shoulders of a bevel, and to a lesser and much more subtle extent, part of the bevel between the shoulder and the apex. I mentioned earlier, that I sometimes use a guided system to set an acute V-bevel, and then follow with maintenance on the hard-backed sandpaper, which then produces the convex in time. The main reason I like setting the initial edge with the guided system, is because of that crisp apex it creates. Any convexing following that, is mainly for smoothing & convexing what's behind the edge, instead of negatively affecting the edge itself. That's what the hard backing does best; as the work gets closer to the edge itself, the convex somewhat flattens out, and it's a more stable surface against which to hone, which protects the apex from being rounded off. With any good cutting edge, whether the steel behind it is uniformly flat or if it's convexed, the edge apex itself will still need to be essentially 'V' in shape, else it won't cut well. This is also why I've gravitated to stropping my edges on very firm or hard backing. Anything to minimize the compression of the substrate, and therefore the rounding effect it has on edges. I also like using my belt as a hanging strop; it's obviously not hard-backed, but the 'free-hanging' nature of it means it's much more difficult to apply excessive pressure, as the belt simply tends to move away from the edge, instead of compressing, when pressure is increased. This is my favorite stropping method for basic carbon steels like 1095 and simpler stainless, like 420HC.


David

 

[HoosierQ]

I am not a huge fan either but I have found that something like a big catalog or a phonebook makes a good backing. There's enough air in between all those pages that it does give a bit but not so much that you get much rounding over. I also have tried that funny stuff that you put under keyboards so they don't slide around...it's like a net with a very thin application of some kind of foam on it...sometimes you see it used also for jar openers. It comes in sheets. Put you sand paper on that. The mousepad method always proved too soft for me. Of course there are different kinds of mousepads too.

 

[Twindog]

A microbevel can be either a V bevel or a convex bevel, just as the main bevel can be a V edge or a convex edge. Either a micro V bevel or a micro convex bevel can be extremely sharp and work extremely well. The geometry is not the problem, only the skill and precision with which that edge is created.

The main advantage of the V edge is that it can be produced with more precision and less skill.

But the problem we have in discussing a convex edge is that the geometry is never defined. It can be anything.

 

[Omega Leather Works]

A microbevel can be either a V bevel or a convex bevel, just as the main bevel can be a V edge or a convex edge. Either a micro V bevel or a micro convex bevel can be extremely sharp and work extremely well. The geometry is not the problem, only the skill and precision with which that edge is created.

The main advantage of the V edge is that it can be produced with more precision and less skill.

But the problem we have in discussing a convex edge is that the geometry is never defined. It can be anything.

Well said.

I've got a bunch of good sandpaper (although most fairly high grit), and I think I'm going to give this a shot. I'm so use to guided systems (and incidentally, they have their own learning curve and "art" if you will) that I have yet to really hone (zing!) my skill with anything freehand. I also believe that they (the methods) complement one another, as I find I learn from both methods, but it's good information regardless of style.

 

[Chris "Anagarika"]

As we are human, trying to sharpen freehand (on stones) will naturally convex the bevel slightly. I don't see how it can be otherwise, maybe an expert like Jason :?:

All my edges are slightly convex this way, having all the stones I have and not wanting to rely on any jigs, that's what I do.

However, convex by conscious attempt (rolling the wrist) and convex by 'accident' (hand position will vary naturally) are two different matter.