Sharpening a convex on the field?

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y53p

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May 11, 2022
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I get the using sandpaper laid on a soft surface, but am I supposed to take sheets of sandpaper with me while camping, along with some paddle strop to lay them on? Is there just a more convenient method, whether with a stone or rod that will get my knife sharp without making it dull in the long run by forming a v edge/deforming the original grind?
 
In actuality, the edge itself will likely stay sharper with the apex being honed to a crisp 'V' edge. It seldom works well to deliberately convex right up to the apex itself. Doing so will widen the apex angle and increase the likelihood of rounding off the apex itself, which will only dull the edge. This is the downside to trying to do a full convex with only sandpaper on a softish, conformable backing - that softish backing will tend to make the sandpaper curl around the apex, which will round it off and dull it.

Just the tiniest of a 'V' microbevel at the apex is enough to keep it keen and crisp. Don't have to make it obvious - even if it's unseen by the naked eye and instead only big enough to be seen under magnification, the V-edge will always be sharper at the apex. Just a handful of passes on something like a medium or fine ceramic hone would be enough to keep it keen, so long as the edge isn't too worn or damaged before attempting resharpening.

Convexing is at its best when the emphasis is placed on the grind of the bevel shoulders behind the edge, without touching the edge itself. The convexed shoulders of the bevels behind the apex will reduce binding in the material being cut. Even better, if the convex behind the edge is thin, i.e., done at very low angle, and is polished and slick. But for the apex itself, if viewed and conceptualized at a microscopic level, it'll always be at its sharpest when it looks like a crisp 'V' with the convex behind it and not immediately at the edge.

So, for field sharpening, leave the sandpaper at home and instead sharpen the apex as needed in the normal fashion, with a stone/hone.
 
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Obsessed with Edges said:
In actuality, the edge itself will likely stay sharper with the apex being honed to a crisp 'V' edge. It seldom works well to deliberately convex right up to the apex itself. Doing so will widen the apex angle and increase the likelihood of rounding off the apex itself, which will only dull the edge. This is the downside to trying to do a full convex with only sandpaper on a softish, conformable backing - that softish backing will tend to make the sandpaper curl around the apex, which will round it off and dull it.

Just the tiniest of a 'V' microbevel at the apex is enough to keep it keen and crisp. Don't have to make it obvious - even if it's unseen by the naked eye and instead only big enough to be seen under magnification, the V-edge will always be sharper at the apex. Just a handful of passes on something like a medium or fine ceramic hone would be enough to keep it keen, so long as the edge isn't too worn or damaged before attempting resharpening.

Convexing is at its best when the emphasis is placed on the grind of the bevel shoulders behind the edge, without touching the edge itself. The convexed shoulders of the bevels behind the apex will reduce binding in the material being cut. Even better, if the convex behind the edge is thin, i.e., done at very low angle, and is polished and slick. But for the apex itself, if viewed and conceptualized at a microscopic level, it'll always be at its sharpest when it looks like a crisp 'V' with the convex behind it and not immediately at the edge.

So, for field sharpening, leave the sandpaper at home and instead sharpen the apex as needed in the normal fashion, with a stone/hone.
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That’s interesting. I’ve heard from people sharpening their convex like they would sharpen a v edge and ending up with dull knives. There’s also a vid on youtube which claims that to be the case (
minute 1:00). Is this true, does the edge end up just becoming a v edge with a chunky convex bevel behind it in the long run?
 
Btw, for reference, I’d be sharpening a Bark River Teddy 2 (if that can offer any insight/additional variables when it comes to the topic at hand)
 
Convex edges are like V edges with the shoulder taken off and blended in. For field sharpening, just sharpen at the apex angle like a standard V edge and worry about maintaining the shoulder when you have a little extra time on your hands. If anything, this method is better controllable for edge angle than sharpening on a soft/flexible backing.
 
y53p said:
That’s interesting. I’ve heard from people sharpening their convex like they would sharpen a v edge and ending up with dull knives. There’s also a vid on youtube which claims that to be the case (
minute 1:00). Is this true, does the edge end up just becoming a v edge with a chunky convex bevel behind it in the long run?
Click to expand...
The 'chunky convex' is more about a very thick primary grind behind the edge, which is what will degrade cutting performance. That thick steel behind the edge also makes it more difficult to sharpen at all, whether convex or v-edge, because the thick steel behind the edge precludes any chance at acute sharpness - the edge angle will always be too wide with such thick steel behind it. That is what will result in dull edges, or edges that don't cut well even after they're sharpened.

For very thick convex blades, the better strategy, which really only needs doing once, is to thin the primary grind out. That's where laying the blade lower to the sandpaper to thin out the grind behind the edge will make the bigger difference. BTW, that's even better-done with a hard backing under the sandpaper, like wood or stone or glass - it'll still convex somewhat when done freehand, but to a thinner and more subtle convex, which will improve cutting performance. Then sharpen the edge as you would any other knife, on a stone. Thinner grinds are much, much easier to sharpen and much easier to maintain sharp, no matter whether the grind is convexed or not.

And a point to remember is, if you're doing the sharpening by a freehand method, whether with a stone or sandpaper, the edge geometry will still convex somewhat, due to the inevitable and natural variability in the held angle. The odds of the edge being sharper will still be better when when it's done on the hard stone, which is what will prevent too much edge-rounding as can happen too easily on softer sharpening substrates.
 
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FortyTwoBlades said:
Convex edges are like V edges with the shoulder taken off and blended in. For field sharpening, just sharpen at the apex angle like a standard V edge and worry about maintaining the shoulder when you have a little extra time on your hands. If anything, this method is better controllable for edge angle than sharpening on a soft/flexible backing.
Click to expand...
Thanks. I’m guessing the best way to take care of the shoulder is with sandpaper as Obsessed with Edges Obsessed with Edges suggested
 
Obsessed with Edges said:
The 'chunky convex' is more about a very thick primary grind behind the edge, which is what will degrade cutting performance. That thick steel behind the edge also makes it more difficult to sharpen at all, whether convex or v-edge, because the thick steel behind the edge precludes any chance at acute sharpness - the edge angle will always be too wide with such thick steel behind it. That is what will result in dull edges, or edges that don't cut well even after they're sharpened.

For very thick convex blades, the better strategy, which really only needs doing once, is to thin the primary grind out. That's where laying the blade lower to the sandpaper to thin out the grind behind the edge will make the bigger difference. BTW, that's even better-done with a hard backing under the sandpaper, like wood or stone or glass - it'll still convex somewhat when done freehand, but to a thinner and more subtle convex, which will improve cutting performance. Then sharpen the edge as you would any other knife, on a stone. Thinner grinds are much, much easier to sharpen and much easier to maintain sharp, no matter whether the grind is convexed or not.

And a point to remember is, if you're doing the sharpening by a freehand method, whether with a stone or sandpaper, the edge geometry will still convex somewhat, due to the inevitable and natural variability in the held angle. The odds of the edge being sharper will still be better when when it's done on the hard stone, which is what will prevent too much edge-rounding as can happen too easily on softer sharpening substrates.
Click to expand...
Thanks for the in depth insight. I’m not sure about the hard-backed sandpaper, sounds like it may be a bit too rough on the blade, leave excessive markings. Also, I found some people advising for micro-meshes (sandpaper with built in foam), would that do the trick to take care of the primary bevel?
 
It can also be done on a conventional stone. In fact, I generally suggest that folks use a flexible backed abrasive mostly for cosmetic purposes in blending in any micro-facets caused by working on a rigid abrasive. A belt grinder with a slack belt does work nicely for a fast powered option.
 
y53p said:
Thanks for the in depth insight. I’m not sure about the hard-backed sandpaper, sounds like it may be a bit too rough on the blade, leave excessive markings. Also, I found some people advising for micro-meshes (sandpaper with built in foam), would that do the trick to take care of the primary bevel?
Click to expand...
Once you get above about 800-grit or so with sandpaper, it'll start trending toward a polished finish, with partial mirror starting around 1000/1200 or so, and then to essentially mirror-polished (as seen by naked eye) at 2000 or higher. You can get a pretty fine satin finish in the 320-600 range. And at 220 or lower, then you'll see something that looks a lot like factory 'satin' finishes.

You can polish the convex further on a hard-backed denim, linen or canvas strop loaded with gray or white aluminum oxide stick compound ('white rouge'). That'll bring up a brighter mirror finish very quickly. For more wear-resistant steels containing vanadium carbides, diamond compound at 3-micron or finer on a hard wood strop will bring up a bright mirror very quickly as well, after following any convexing done at 600/1200 or finer in diamond.

I've tried something similar to the micro-mesh before. They're pretty good at polishing, but seem slower than other methods as with the 2000+ grit sandpaper and/or the denim strop loaded with white rouge. I largely DON'T like anything with a soft backing (foam, leather, mouse pad, etc.), simply because they're much more prone to rounding off the edge as I mentioned earlier.

One trick for easier convexing, while minimizing the edge-rounding caused by too-soft substrates, is to lay a single sheet of plain copy/printer paper underneath the sandpaper, over a hard backing like glass or stone. Just that one extra layer of paper, at maybe 3 mils (0.003 inch) thickness, is just enough 'cushion' to allow for clean convexing without getting too soft or conformable underneath the sandpaper. Can also do this up to maybe 2 or 3 sheets of paper - but I wouldn't take it any thicker than that.
 
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Obsessed with Edges said:
Once you get above about 800-grit or so, with sandpaper, it'll start trending toward a polished finish, with partial mirror starting around 1000/1200 or so, and then to essentially mirror-polished (as seen by naked eye) at 2000 or higher. You can get a pretty fine satin finish in the 320-600 range. And at 220 or lower, then you'll see something that looks a lot like factory 'satin' finishes.

You can polish the convex further on a hard-backed denim, linen or canvas strop loaded with gray or white aluminum oxide stick compound ('white rouge'). That'll bring up a brighter mirror finish very quickly. For more wear-resistant steels containing vanadium carbides, diamond compound at 3-micron or finer on a hard wood strop will bring up a bright mirror very quickly as well, after following any convexing done at 600/1200 or finer in diamond.

I've tried something similar to the micro-mesh before. They're pretty good at polishing, but seem slower than other methods as with the 2000+ grit sandpaper and/or the denim strop loaded with white rouge. I largely DON'T like anything with a soft backing (foam, leather, mouse pad, etc.), simply because they're much more prone to rounding off the edge as I mentioned earlier.

One trick for easier convexing, while minimizing the edge-rounding caused by too-soft substrates, is to lay a single sheet of plain copy/printer paper underneath the sandpaper, over a hard backing like glass or stone. Just that one extra layer of paper, at maybe 3 mils (0.003 inch) thickness, is just enough 'cushion' to allow for clean convexing without getting too soft or conformable underneath the sandpaper. Can also do this up to maybe 2 or 3 sheets of paper - but I wouldn't take it any thicker than that.
Click to expand...
What should the angle be when working on the primary bevel? Slightly lower? Say v edge was 20, would I have to go for around 10-15?
 
y53p said:
What should the angle be when working on the primary bevel? Slightly lower? Say v edge was 20, would I have to go for around 10-15?
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Basically, you just want to make sure it's low enough to keep the paper from contacting the apex of the edge. How low that is depends on how soft the substrate is under the sandpaper and how much pressure you're using.

You could use the Sharpie method to ink the bevels all the way to the edge. Then look to take the ink off only behind the edge. With some experience, you'll get a better feel for how low you need to hold the angle and you'll be able to feel if the edge itself is beginning to make contact with the paper.
 
If you are not using your full convex knife very hard, you can also keep it reasonably sharp by stropping often while in the field. Definitely figure out the correct angle at home before you go. Maybe you do this already.
 
Best method is a guided sharpener with a covexing rod. Depending on knife steel i am btwn 17-23 with a 4 degree difference in my angle and it performs better than anything else ive ever used.

Unless im cutting rocks or other knives i wouldnt need to touch an edge in the field. I also run super steels and sandpaper wouldnt sharpen them
 
You can easily sharpen convex edges in the field simply by stroking backward instead of edge forward. I've used this technique with DMT Diafolds for decades.
 
In the field you could use a mouse pad with sandpaper on top (edge trailing). Convex edges are stronger and allow changing directions more easily while cutting. In the field it might be difficult to find a flat surface on which to place the mouse pad.
 
Obsessed with Edges said:
In actuality, the edge itself will likely stay sharper with the apex being honed to a crisp 'V' edge. It seldom works well to deliberately convex right up to the apex itself. Doing so will widen the apex angle and increase the likelihood of rounding off the apex itself, which will only dull the edge. This is the downside to trying to do a full convex with only sandpaper on a softish, conformable backing - that softish backing will tend to make the sandpaper curl around the apex, which will round it off and dull it.

Just the tiniest of a 'V' microbevel at the apex is enough to keep it keen and crisp. Don't have to make it obvious - even if it's unseen by the naked eye and instead only big enough to be seen under magnification, the V-edge will always be sharper at the apex. Just a handful of passes on something like a medium or fine ceramic hone would be enough to keep it keen, so long as the edge isn't too worn or damaged before attempting resharpening.

Convexing is at its best when the emphasis is placed on the grind of the bevel shoulders behind the edge, without touching the edge itself. The convexed shoulders of the bevels behind the apex will reduce binding in the material being cut. Even better, if the convex behind the edge is thin, i.e., done at very low angle, and is polished and slick. But for the apex itself, if viewed and conceptualized at a microscopic level, it'll always be at its sharpest when it looks like a crisp 'V' with the convex behind it and not immediately at the edge.

So, for field sharpening, leave the sandpaper at home and instead sharpen the apex as needed in the normal fashion, with a stone/hone.
Click to expand...

Agreeed, I put convex edges on all my knives with simple pocket stones.

OP, just need to loosen your wrist a bit and let the blade naturally rock back and forth when sharpening.
 
tiguy7 said:
In the field you could use a mouse pad with sandpaper on top (edge trailing). Convex edges are stronger and allow changing directions more easily while cutting. In the field it might be difficult to find a flat surface on which to place the mouse pad.
Click to expand...
Convex edges are actually equivalent to a conventional V edge with the shoulder knocked down and blended in. They are technically "weaker" than V edges at equal edge angle due to this removal of material behind the edge, but the relief in material does allow them to move through material easier and make turns in the cut better. If your convex edge is stronger than a V edge it is because the apex is at a thicker angle, nothing more.
 
FortyTwoBlades said:
Convex edges are actually equivalent to a conventional V edge with the shoulder knocked down and blended in. They are technically "weaker" than V edges at equal edge angle due to this removal of material behind the edge, but the relief in material does allow them to move through material easier and make turns in the cut better. If your convex edge is stronger than a V edge it is because the apex is at a thicker angle, nothing more.
Click to expand...
I like a stronger edge (with the thicker angle on the apex) on chopping tools.
 
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