Convex Sharpening? The Straight Scoop Please?

[JD Spydo]

I kind of pride myself as being above average at most knife sharpening. I must be at least fair because I'm constantly having people pay me to sharpen a lot of their knives and edges tools. I've got most of Spyderco's great sharpening tools as well as a huge selection of benchstones, Strops, ceramic files, diamond files and benchstones and a lot of obscure sharpening tools as well. At this time I've got my Spyderco M390 Military so sharp that it goes through cigarette rolling paper like warm butter. So I'm not really a novice at sharpening but really not what I consider good at Convex Sharpening.

OK with all that being said I've made a commitment that I want to now learn how to do "Convex Sharpening" ( especially on knives"). I had the great priviledge of getting to chat with the late Bill Moran before he passed away and he told me that the convex edge was the best and he went into a lot of reasons why. I believed him and I've thought about it a lot over the years.

So can any of you recommend any books, videos or point me to a website for a source for "Convex Sharpening"? Actually I want to learn to do it the correct way. I've made some attempts at it but I'm not 100% satisfied with the results I've obtained up till now. I know that many of you guys are probably even expert in that field. But I want to know the exactly correct and best way to do it. OK I'm all ears at this point

 

[cbwx34]

I'll ask the obvious question first... if you're freehand sharpening, are you not already convex sharpening? Or are you looking for something else?

p.s What "obscure sharpening tools"?

 

[maximus83]

Pinging HeavyHanded , and Jason B. to weigh in on thread if they're around.

OP I'm in the same place of wanting to get better at convex, this thread is as good a place to discuss as any. Recently got a regrind that put a nice full convex on a folder, and another one where I had a flat grind on a mora, and convexed the edge myself on a friend's belt grinder, and another mora that I manually ground on a stone from scandi to full convex (still working on that one on weekends, it's mostly a learning project with a throwaway knife). I've tried some of the standard BRK propaganda, 'mousepad sharpening' and all that, and not really that pleased with the results. It works, I've tried it and many use it with decent results. But there has to be a better way than having that variable surface of the mousepad that is not fully under your control. And besides, there are times especially with big chopping tools that you actually need to do some real sharpening/grinding to reshape and repair edges. In those cases, a mousepad doesn't really cut it.

I've had a few discussions with Jason and Martin about this, and really just getting started with convex myself, not expert at all. But I think you could start with a few ideas I've gotten from them and guys like Murray Carter on YT. Here are some things I'm trying:

• Use a wrist-rocking motion to sharpen. You can see this demonstrated by Carter in his convex sharpening YT videos.
• Sharpen your convex on HARD stones, not mousepads.
• You can maintain a convex on a HARD strop with compound, using the same wrist-rocking motion. For example, I have a strop with linen on a hard glass backing, and cbn compound. I maintain my convex folder on that strop followed by a clean leather strop using a wrist rocking motion, and I haven't had to sharpen it, at all. This approach was recommended by @razor-edge-knives, who did the regrind on the folder, and it works quite well to maintain an already sharp convex blade.
• If your blade is a full convex, you are of course always to some degree touching the primary grind, and this can have a bad impact on the appearance of your blade, especially when you grind on coarse stones. To compensate, you may need to use wet/dry sandpaper, again on a hard-backed surface, to help even out the finish. There are a lot of tools you could rig up or buy to do that, including just wrapping some sanding paper tightly around a bench stone. Jason tipped me off to this handy sanding block by JRE industries, makes it really easy to quickly attach sandpaper. I mount the block in a hobby vise, bottom up, so I can sharpen on the sandpaper just like a bench stone.

 

[JD Spydo]

I'll ask the obvious question first... if you're freehand sharpening, are you not already convex sharpening? Or are you looking for something else?

p.s What "obscure sharpening tools"?

All the obscure sharpening tools I've gather over the years>> do you have about 3 hours for me to list them all ?? I used to buy a lot of really strange sharpening tools from Garrett Wade, JapanWoodWorker, Lee Valley and a few other sources. I've got quite a collection I've accrued over the years. I still don't know what to use those weird Tungsten Carbide tools I got from Garrett Wade for>> but I'm sure they will come in handy for something eventually.

Actually I do a lot of freehand sharpening on some of my Benchstones ( mostly my Spyderco 302 Benchstones) but I'm coming up with a conventional triangular/apex type edge for the most part. But I believe what the late Bill Moran told me and I want to learn maybe just exactly how him and other bladesmiths did it.

I'm welcoming all input I can get>> because I get the feeling that Convex Sharpening would probably go with the old adage that states "There's More Than One Way To Skin A Cat" so to speak>> and I'm sure there are probably at least a half a dozen good methods for Convex Sharpening. I've tried the MousePad method with some modest success but I know I can do better than that.

 

[Twindog]

Just saying you want to put a convex edge on a blade doesn't tell you much. A convex edge can be virtually identical to a V edge. It can be more or less acute than a V edge. It can be more robust or more fragile than a V edge. Any old convex edge is not likely to be what Bill Moran was putting on his edges.

So saying a convex edge is superior or inferior to a V edge is meaningless.

What you really want to do is determine how the blade will be used, taking into account its overall geometry and its steel and heat-treat characteristics. Then you design a geometry for the blade's edge that can handle those cutting tasks the most efficiently without damage.

Form is not function. Form follows function.

 

[EdgePal]

i invented the first tecnical solution for shapen true convex edges for soon 20 years ago, the bended, or angled, guide rod. All my shapening tools have sins then been delivered with both a straight guide rod for straight edges and a bended or angled guide rod for true convex edges.

A straight guide rod force the sharpener to go straight across the edge - and it will give a perfect straight flat edge.
The bended, or angles, guide eod force the shapener to make a controlled curve across the edge - exactly the same curve every time.
This means that with a bended, or angled, guide rod you an use both degrees on the convex cutting edge - and you can decide how many degrees your convex sphere shall hold.

So, if you have, for example a Lansky sharpening tool, you can also make controlled true convex edges - but you are limmited to the four fixed degrees there is on a Lansky (not exactly the four degrees - and I shall try to explain this below).

What you need to do with one of the Lansky guide rods is to bend the small 90 degree bend there is to lets say 100 degrees - so that the small bended part will be more bended then it is. When you mount this bended guide rod in to the sharpener, the sharpener will now be in 10 degrees angle from the long part of the guide rod. Now can you shapen a true convex edge.

To use degrees you need to have an Angle Cube or similar. Mount the Lansky body in a vice so that it is fixed in its position. It is nice if you can fix it in, for example, 10 degrees with the clamp pointing up. Clamp a knife. Lay sown the sharpener on the edge, use Angle Cube on the top of the sharpener, zero the Angle Cube - and then move the sharpener forward with the Angle Cube standing in the same position - and read how many degrees the edge angle changes between the a
Short ends of the sharpener.

I make a tool named Chef. Chef delivers, as all my tools, with a angled guide rod dor convex edges. The distance between the cutting edge and the pivot point is allways 28 cm. This distance make that for every 25 millimeter (1") i use id the sharpener length It change the sharpeners angle 1 degree. This means that I, on my tool Chef, can use 7,5 centimeter (3") if the sharpeners length Tomane a 3 degrees true convex edge. To do this I use stopcollars and small springs on the guide rod that decides how long I can use of the length of the sharpener. This decide the starting point and the end point = the sharpener have fixed starting point and fixed end point = the sharpener mqke exactly the same convex curve in every stroke = this means that I can decide both what degrees I like ro have on the convex edge and that I can decide how many degrees convex sphere I lika to have.
Of couse, it also means that I can repeat it as many time I like.
(Chef have a built in protractor so I do not need a Angle Cube to meaasure the angles. Chef allways have 28 cm distance between the cutting edge and the pivot point, this is possible becouse Chef is also adjustble for different blade width).

If you, on your Lansky, guide rod, mount the sharpener in different places on the guide rods bended part you will also get different degrees in the same Guide rod opening for degrees where the guide rod slades thru. How much the angle changes you need a Anle Cube to meassure.

So, if you have a Lansky, Gatco, DMT Alinger or similar, bend one of your guide rod as I describe above, meassure the angles with an Angle Cube - and you can make true convex edes on your knifes if they have the correct blade length for the tool you use.

I started to explain this for soon 20 years ago on Knifeforum and Bladeforum - and there was a very hard and big resistance against it.
Today the bended/angled guide rod is accepted all over the world - but I was forced to work hard for it during many years.

You are, as a privet person, alloude to make and use a bended or angled guide rod for privet use - and also when you sharpen knifes for other people.

Thomas

 

[EdgePal]

Twindog, I agree

A Fallkniven convex sphere are around 6 degrees, Bark Rivers convex spheres is 2-3 degrees and most convex edges holds 3-4 degrees convex spheres. They work very differently and penetrera materials very differently.

What type of edge you shall use decides from what you need your knife to do for you, you can choose flat, convex, hollow, and so on, edge in wanted degrees. If you choose convex edge you also need to decide what convex sphere you like to have that fits your needs.

Convex edges are absolutley not better or superial then other types of edges, it is just a type of ede you choose that fits just your needs.

Thomas

 

[Jason B.]

The straight scoop?

There is almost a mythical fantasy that surrounds the convex blade/edge and has lead to a lot confusion. Convex is basically a way to make a thick blocky object smoother so it passes through other softer object easier. By reducing the surface contact area and friction you allow a thick blade to cut with the same resistance as a much thinner blade through the same object while maintaining more rigidity. Don't get consumed in thinking just about the sharpened edge though, the blade geometry is far more important and makes the most notable difference.

Convexing on a soft backing like the JRE block is not nearly as easy as is lead to believe. Using the right pressure depending on the part of the blade you are sharpening and the amount of convex needed is something that can take time to learn. I would highly recommend the JRE block though, it was a game changer for me with convex edges.

Convexing on a hard surface such as a high density waterstone is not all that pretty and sounds much harder but it's a lot easier and faster than other methods. The finish will never be what you get with sandpaper but if you use the blade then you will appreciate the convenience of sharpening with stones.

Personally, I'm not a big fan of convex edges because they do little for the performance of the blade and make sharpening of the secondary edge harder. The geometry that really matters is the blades primary grind geometry and if the blade is a full height convex you will have one awesome cutting tool regardless if the secondary bevel is convex or stone sharpened to a V bevel.

 

[maximus83]

The geometry that really matters is the blades primary grind geometry and if the blade is a full height convex you will have one awesome cutting tool regardless if the secondary bevel is convex or stone sharpened to a V bevel.

This part is interesting to me and I've noticed a couple of recent alternative approaches with knives I've acquired:

* Convex primary grind + very tiny v-grind at the edge. Example: a Tojiro Japanese chef knife recently acquired from CKTG. That thing cuts like a laser.
* Full flat primary grind + convexed edge. Recently I tried this approach with a Mora Garberg knife. FortyTwoBlades ground it to a FFG when I bought it from him, then I convexed just the edge. Honestly, I notice significantly improvement performance in slicing hard food (like apples, cheese, etc.) with that convexed edge versus the v-edge I had on there before.

I don't see either of these approaches used widely, but I do see both used to good effect, like the 2 examples that I've experienced.

What do you think of those 2 approaches to using convex, and do you like one more than the other as a general sharpening strategy?

 

[HeavyHanded]

Pretty much this ^, esp sharpening them on stones. Hard backed wet/dry or a softer waterstone work well for cosmetics. A hard stone is better for correcting geometry if needed.


Are you doing it by hand or on a machine of some sort?

I use a sharpie and make radial lines from spine to edge - grind away.

It helps to concentrate on the region right behind the actual edge, as on a convex it only takes literally a couple of swipes to do the actual cutting edge on a hard stone.

I like them for choppers and if ground nice and thin for utility cutting on some knives. They do not steer as well as a thin flat primary, but are a great solution to indefinitely maintaining an edge with consistent geometry. They are a great quick fix for overbuilt sabre ground primary edges - not as good as a full regrind at a lower angle but a huge improvement anyway.

 

[willc]

I guess I convex my edges, most knives come at 20 degrees or so and the first thing I do is grind the shoulder off a bit below 13 degrees but I normally stop grinding about 2/3 of the way to edge.

Then I work a slightly more obtuse angle(about 15) from edge back and the flat ends up being 2/3 or so back from my now rounded shoulder.

I started doing this a while ago as it is a preemptive type thinning.
Eventually in a few sharpening sessions I can bring the flat edge to once rounded shoulder and have a V grind but I normally just keep with the rounded shoulder so I guess I am doing a convex without a mouse pad.

 

[JD Spydo]

Just saying you want to put a convex edge on a blade doesn't tell you much. A convex edge can be virtually identical to a V edge. It can be more or less acute than a V edge. It can be more robust or more fragile than a V edge. Any old convex edge is not likely to be what Bill Moran was putting on his edges.

So saying a convex edge is superior or inferior to a V edge is meaningless.

What you really want to do is determine how the blade will be used, taking into account its overall geometry and its steel and heat-treat characteristics. Then you design a geometry for the blade's edge that can handle those cutting tasks the most efficiently without damage.

Form is not function. Form follows function.

It's an interesting litany of what you said overall. Because when you think about it I've never seen a straight razor with a convex edge and they are probably about the sharpest edged tools out there. But an edge that thin is probably very fragile for any job other than shaving your face.

What the other fellow said about blade geometry really factors in as well because I have had great results overall with full flat grind blades>> especially my trusty Spyderco TEMPERANCE 1 model ( in SE & PE both).

I do remember Bill Moran drawing a rough picture of what his edges usually looked like after the knife was finished and it sure had a beefy shoulder to it. I'm wondering now if the type of abrasive used on the type of blade steel you might be using would actually be the key to ultimate sharpness?

 

[maximus83]

Pretty much this ^, esp sharpening them on stones. Hard backed wet/dry or a softer waterstone work well for cosmetics. A hard stone is better for correcting geometry if needed.


Are you doing it by hand or on a machine of some sort?

If asking me, the knives I referred to are a mixed bag. The CKTG chef knife I just bought that way. The garberg I mentioned was done on belt grinder. My mora project knife I'm doing regrind by hand on stones plus the JRE block. Goal, same as OP, is to figure out a repeatable method to maintain convex with hand sharpening, using a combo of my regular stones plus the JRE block with sandpaper.

I like them for choppers and if ground nice and thin for utility cutting on some knives. They do not steer as well as a thin flat primary, but are a great solution to indefinitely maintaining an edge with consistent geometry. They are a great quick fix for overbuilt sabre ground primary edges - not as good as a full regrind at a lower angle but a huge improvement anyway.

This is what I'm trying to figure out. What are the optimal function/uses of convex? You list good examples. I have some convexed axes and choppers that really are effective, so I see that firsthand. But then I have large ESEE Junglas chopper blades that are flat grinds, and in my results and earlier testing Cliff Stamp posted, those ESEE blades are phenomenal light choppers too. But either way, even with the convex, sometimes I knock big chunks out of the blade on choppers and axes. That's part of the reason to learn to actually sharpen them on stones, I can't easily fix those big dings on a mousepad. On smaller utility knives, I think a lot of the knife user community agrees, what is really optimal there is a thinner primary grind if you're going to do a full convex. I've noticed that some of the most popular recent BRK models of convexed field knives in premo steels are the "LT" (= light?) models where they have a much thinner primary grind. Those knives are consistently sold out vs the thicker grind models.

 

[maximus83]

For those interested, here's a pic of the JRE block bottoms up in the small vise.

Getting back to the OP's asking about methods, I'm hardly the one to advise on expert convex sharpening, but thinking just the basics from talking to other guys, I think it boils down to:
* There's a place for using ordinary bench stones. As discussed above.
* There's ALSO a place for using something like the JRE here, or similar, which has a little give to it (the same principle of using mousepads).

The trick for me, is learning how to use these 2 approaches IN COMBINATION to get the results I want. I haven't yet seen a good end-to-end method demonstrated on how to do that. So I'm using cheap mora carbon steel 'project knives' to learn. What I'm thinking simplistically is that maybe you do your coarse grinding/shaping on the hard stones, then you use the soft-backed solution like the JRE to refine and even things, and also to make the finish look better if the cosmetics matter. But open to any suggestions from folks who've done a lot of this, I'm all ears.

 

[Chris "Anagarika"]

We’ve gone through enough Convex vs V grind debates . In my view, final apex is always a V mathematically, the supporting steel right at the apex bevel can be a V or convex depending on level of magnification. Primary grind is obviously Moran apple seed as opposed to Spyderco Endura Sabre, Manix 2 hollowed and Endura FFG.

J JD Spydo , which one you’re looking for?

Already mentioned, in some applications, the shoulder of the sabre might be useful to wedge the material away. In others, smooth flow of convex might be better. I don’t think there’s any general answer.

PS: I am currently chasing after flat V as much as possible when free handing, so I can achieve better edge because of consistency.

 

[HeavyHanded]

If asking me, the knives I referred to are a mixed bag. The CKTG chef knife I just bought that way. The garberg I mentioned was done on belt grinder. My mora project knife I'm doing regrind by hand on stones plus the JRE block. Goal, same as OP, is to figure out a repeatable method to maintain convex with hand sharpening, using a combo of my regular stones plus the JRE block with sandpaper.

Basically if using a belt grinder you have to figure out a way to control the angle at two points. One is always going to be the apex angle, and the other is where on the primary the convex stops. With practice you can get pretty good at stopping on the spine by feel, and the rest is just studying where the metal is coming off as you work toward the apex.

By hand the easiest way is with a benchstone to remove metal along the entire convex surface using a rolling action. Once it gets reset, you can switch to wet/dry over a hard backing. If you have a smooth technique, you can go through several stone progression and finish it off on a strop or even just stop at the finest stone you planned on using. Cosmetically, the second approach will not look as nice as the one finished on wet/dry, even if done on softer waterstones - but you can get very close and certainly acceptable both cosmetic and cutting with enough practice.

This is what I'm trying to figure out. What are the optimal function/uses of convex? You list good examples. I have some convexed axes and choppers that really are effective, so I see that firsthand. But then I have large ESEE Junglas chopper blades that are flat grinds, and in my results and earlier testing Cliff Stamp posted, those ESEE blades are phenomenal light choppers too. But either way, even with the convex, sometimes I knock big chunks out of the blade on choppers and axes. That's part of the reason to learn to actually sharpen them on stones, I can't easily fix those big dings on a mousepad. On smaller utility knives, I think a lot of the knife user community agrees, what is really optimal there is a thinner primary grind if you're going to do a full convex. I've noticed that some of the most popular recent BRK models of convexed field knives in premo steels are the "LT" (= light?) models where they have a much thinner primary grind. Those knives are consistently sold out vs the thicker grind models.

In my practice they work best on choppers. Hatchets, machetes. It is much easier to maintain in the field using a circular grinding motion to a convex grind with a smaller stone than to attempt a flat bevel.

I also like the slightest of convex on my chisels, or at least a flat grind with a sight freehand convex. My use of wet wheel hollow grinds on these tools resulted in more wedging - but might also be my technique.

For smaller utility cutters I don't find any real difference between convex and flat grind of comparable spine thickness and terminal edge angle. As the knife becomes more overbuilt the convex has more to offer.

 

[FortyTwoBlades]

The difference in performance will be small, but the higher and thinner the convex is brought the better performance will be in deep cuts, as there will be a longer "ramp" involved doing the deflection. Unless you increase the edge angle by accident, in which case there will be an increase in the steepness of that ramp before it levels out. Imagine you have a heavy, tippy wheelbarrow and you're trying to get it up a ramp shaped like the blade geometry. If it's steep right at the bottom of the ramp you may need a running/forceful start to get it up over that hump to the smoother transition zone. If the top of that ramp is cut down smoother, it suddenly takes much less effort to get up that ramp even if the angle at the bottom is the same (just shorter)

 

[Obsessed with Edges]

(...) The trick for me, is learning how to use these 2 approaches IN COMBINATION to get the results I want. I haven't yet seen a good end-to-end method demonstrated on how to do that. So I'm using cheap mora carbon steel 'project knives' to learn. What I'm thinking simplistically is that maybe you do your coarse grinding/shaping on the hard stones, then you use the soft-backed solution like the JRE to refine and even things, and also to make the finish look better if the cosmetics matter. But open to any suggestions from folks who've done a lot of this, I'm all ears. (...)

When I first explored it, I found that establishing the overall shape of the convex was easier when done on the softer backing. The conformity of the backing is what does the shaping; it's virtually automatic and easier for a novice to execute cleanly. And from that end, a good way to regulate the process (for me) was to use varying thicknesses of stacked paper underneath my sandpaper. I used a varied number of printer paper sheets for this, over a granite reference plate or a glass plate. More sheets of paper underneath = more 'give' to the backing and a more obvious & thicker convex; fewer sheets = less 'give' and a shallower, thinner convex. Fewer sheets also means the sandpaper works more aggressively for it's rated grit, producing faster results. This is a big advantage when trying to knock down the very crisp shoulders on a very thick & heavy V-bevelled edge. Otherwise, trying to reduce those shoulders over a softer backing can get excruciatingly slow, and makes for a very obtuse edge as well. Another workaround for that: thin the edge to better geometry first, on stones or whatever, and THEN set about doing the convex afterward. I usually reprofiled to < 30° inclusive or lower, before attempting convexing. A little lower in angle is better, starting out, as the finished convex will likely widen the edge angle a little bit, by the time it's all finished.

For refining the edge, after shaping the convex, going firmer with the backing is ALWAYS the better approach to keep the edge crisp and minimize rounding of the apex. In my case, when I first tried it, that meant I minimized the layering of paper underneath my sandpaper, or eliminated the paper layering altogether. Taking that further, finishing the edge directly on a stone will produce better results still.

Nowadays, if I'm looking to deliberately convex an edge, I use hard stones/hones for all the shaping, using a back/forth scrubbing stroke which naturally introduces a little rocking motion, producing the convex. A well-lubricated stone/hone helps in keeping the motion smooth & easy, which improves the aesthetics of the convex overall. I do the apexing with edge-leading only, for the best sharpness. I follow that with stropping on a hard strop, like denim-over-wood, or a basswood block alone and some aggressive polishing compound. For more mainstream steels, aluminum oxide compounds work well on the denim strop. With more wear-resistant steels, 3 micron diamond paste has been my favorite, used on basswood.