Why an edge bevel and why not more convex grinds.

[Korean Hog]

One advantage of an edge bevel over full flat or convex grinds is that you don't have to sharpen the entire blade flat, just the bevel.

I prefer an edge bevel for this very reason, if I'm going to sharpen the whole primary bevel I prefer to work up through japanese water stone grits because I don't like the way deep scratches look and on a "normal" edge bevel 50 strokes on a medium diamond will get me back to work for another hour or two.

 

[FortyTwoBlades]

You don't have to sharpen the whole blade with convex grinds. Those who assert you do don't really understand what's meaningful about the geometry. All sharpening occurs in two major stages: shaping and honing. Honing can be done just at the edge until the geometry has thickened to the point of meaningfully impacting cutting performance, at which point you'll go back to the shaping stage to restore the proper gross geometry. This is why understanding the role that specific geometry both at and behind the edge is so important, and these factors are largely ignored in favor of more readily observable cosmetic factors or superficial traits that are really unimportant except for how they relate to the fundamental root geometry.

 

[Twindog]

You don't have to sharpen the whole blade with convex grinds. Those who assert you do don't really understand what's meaningful about the geometry. All sharpening occurs in two major stages: shaping and honing. Honing can be done just at the edge until the geometry has thickened to the point of meaningfully impacting cutting performance, at which point you'll go back to the shaping stage to restore the proper gross geometry. This is why understanding the role that specific geometry both at and behind the edge is so important, and these factors are largely ignored in favor of more readily observable cosmetic factors or superficial traits that are really unimportant except for how they relate to the fundamental root geometry.

The problem is that if you just "hone the edge" you're creating an edge bevel, so the blade is no longer full flat or full convex ground.

 

[FortyTwoBlades]

The problem is that if you just "hone the edge" you're creating an edge bevel, so the blade is no longer full flat or full convex ground.

That is not a problem, though; that's what I'm saying. Until you have worn far enough back into the geometry for it to cause a noticeably negative effect on the cutting performance, you don't need to worry about it being "true" to the definition. That's an arbitrary trait that's unimportant to the function of the tool.

 

[Twindog]

Another problem with full grinds is that you need to have either a very acute edge or a very thick blade.

Convex grinds do not have angles, but you can see the issue with a full flat grind.

Say your blade is 1.2 inches wide and you grind it to a 30 degree inclusive edge. That's a fairly aggressive edge at 15 dps. Most people here use a 20 dps edge.

But with this blade 1.2 inches wide and with a 15 dps full flat grind, you have a blade that's 0.64 inches thick at the spine.

 

[Twindog]

That is not a problem, though; that's what I'm saying. Until you have worn far enough back into the geometry for it to cause a noticeably negative effect on the cutting performance, you don't need to worry about it being "true" to the definition. That's an arbitrary trait that's unimportant to the function of the tool.

I understand what you're saying. The issue is that by honing in an edge bevel, it's no longer a full convex or full flat grind. It's a grind with an edge bevel.

If you want to keep it full convex or full flat, you have to sharpen the full blade flat.

 

[James Y]

The only gripe I have with CRK knives is that, while the entire blades are hollow-ground, the edge bevels are convex. IMO, CRKs would cut better out of the box with standard V-ground bevels. Again IMO, that would better complement the high hollow grind on most CRKs than the convex bevels. I haven't found them particularly hard to sharpen, but out of box they tend to have less bite than V-ground edge bevels would, and I haven't found that the convex bevels necessarily improve edge-holding over V-ground edge bevels (on a pocket knife).

Then again, my post is probably OT for this thread.

Jim

 

[PirateSeulb]

That seems on topic giving an example of a knife with a convex grind out of the box that may not be suited to such a grind.

 

[rileybassman1]

Do you have any experience with the KME convex rod? I'm wondering if it actually works. I have the KME system and a bunch of barkies.

I have it and have used it on some barkies as well as some fiddlebacks. I think it works good... you have to pay attention to using the entire length of the stone as to get full convex effect. When finished it tends to look slightly more like a V grind... but after restoring an edge with the KME, I hit it with sandpaper and mousepad - usually 1k, 2k, 3k then strop. that takes out the "look" of a secondary bevel and works quite well. I have gotten the 3 or so I have done it with extremely sharp.

I would say I usually still maintain with strop/sandpaper, but in the future, any edge damage or big sharpening jobs I will use it.

 

[FortyTwoBlades]

I understand what you're saying. The issue is that by honing in an edge bevel, it's no longer a full convex or full flat grind. It's a grind with an edge bevel.

If you want to keep it full convex or full flat, you have to sharpen the full blade flat.

You can field-hone with a microbevel and reset to zero back at home. But if you're freehanding it you're still gonna' end up with a convex. Very, very few knives a full flat zero grinds, and those are fairly easy (if slow) to hone up since you just lay the blade flat on the stone.

 

[marcinek]

Convex grinds do not have angles

 

[r8shell]

There you go, off on a tangent again.

 

[USMCPOP]

It seems to me that convexing a v grind works out real well but trying to make a V grind or put a secondary bevel on a convex/ scandi grind kind of comes out like crap.

Most of my blades with a secondary bevel get convexed over time and my convex grinds have a bit of a micro-bevel because I sharpen by hand usually with a 4-5" pocket stone.

Yeah, I have a lot of convexed stuff. Did a lot of sharpening of big knives in Thailand. When the natural stone gets worn down to a swayback shape and you're rocking back and forth, stuff gets convexed. I start flat to get the rust off the big choppers, raise up a bit to kind of keep the profile and get to the edge. I finally get bored and raise a bit more and maybe get a micro bevel so I can shave hair. Not pretty, but functional.

 

[USMCPOP]

You don't have to sharpen the whole blade with convex grinds. Those who assert you do don't really understand what's meaningful about the geometry. All sharpening occurs in two major stages: shaping and honing. Honing can be done just at the edge until the geometry has thickened to the point of meaningfully impacting cutting performance, at which point you'll go back to the shaping stage to restore the proper gross geometry. This is why understanding the role that specific geometry both at and behind the edge is so important, and these factors are largely ignored in favor of more readily observable cosmetic factors or superficial traits that are really unimportant except for how they relate to the fundamental root geometry.

FortyTwoBlades , I think I was trying to say a similar thing.

 

[gadgetgeek]

A factor will also be the desired aesthetic. Some will look at a slack-belted knife and no matter how "perfect" everything lines up, they will find that it doesn't look right. Take a plas or waterjet cut knife, make all those same grind lines nice and crisp, and some will find it "unfinished"
At the end of the day, you like what you like.