Convex edge sharpening

[Danketch]

Convex is the first grind I can actually get hair shaving sharp without a guided system. I have a bunch of Bark Rivers, in A2 and 3V. I think most of them coming from the factory need to have their shoulders thinned some before actually using/getting real sharp. Even though the owner says they don't come with a microbevel, it sure as heck seems like they have something there that is not a true zero degree convex edge. I used a DMT Diafold coarse/fine with circular, scrubbing motions to relieve mine and get an actual hair shaving edge off the coarse side.

HeavyHanded's advice (and videos, and Washboard sharpening system) are great for convex edges. Especially the radial sharpie lines trick.

I hate the idea of putting a v-grind on a convex. Defeats the purpose to me. Don't give up and read the stickies and watch some videos and try again. VirtuoVice (on youtube) also has some good (if rambling, and kind of hard to understand) videos on Bark Rivers and convexing, just don't overstrop like he does.

 

[BDay]

The bevel I put on this knife bothers me too. Later when I really stopped and thought about it I could see that all I probably needed to do was increase my angel just a bit to move the work to the edge. Something I was reading about chisel sharpening today was saying that it is easy to be doing a lot of work that doesn't get to the edge. Which is what I had been working on to remove the bevel.

I am going to buy some cheap knife with a bevel edge and practice on that.

In the end I need an edge I can maintain in the field, I know I can do that with a couple of tools on a bevel, and I see people doing the same with convex.

Thanks!

 

[Fred.Rowe]

There are two distinct types of convex edges. The ones accomplished freehand on a hard surface, a diamond plate or stone, if done with skill result in a flat cutting edge with the shoulders intentionally rounded off.
Convex edges accomplished on a soft surface, mouse pad or slack belt, are convex from the rounded shoulders clear through the apex; to me there is no advantage to this type of convex edge. It removes more metal than is necessary to attain the same level of sharpness done on a hard surface or a controlled system where the result is a "flat" cutting edge.

Convex works, I agree wholeheartedly, but the the reason it works has more to do with the apex being contacted by the abrasive when using this technique, than it has to do with the resulting geometry.

The view of a "flat" edge proponent, Fred

 

[HeavyHanded]

There are two distinct types of convex edges. The ones accomplished freehand on a hard surface, a diamond plate or stone, if done with skill result in a flat cutting edge with the shoulders intentionally rounded off.
Convex edges accomplished on a soft surface, mouse pad or slack belt, are convex from the rounded shoulders clear through the apex; to me there is no advantage to this type of convex edge. It removes more metal than is necessary to attain the same level of sharpness done on a hard surface or a controlled system where the result is a "flat" cutting edge.

Convex works, I agree wholeheartedly, but the the reason it works has more to do with the apex being contacted by the abrasive when using this technique, than it has to do with the resulting geometry.

The view of a "flat" edge proponent, Fred

In bold. I really do not advocate using conformable backing beyond a few sheets of paper or a single layer of wet/dry over a hard surface etc. I slight bit of give just for cosmetic sake. Using materials that form the entire curve can be very problematic - better to form it on a hard surface and have total control over the shape of the curve and the final edge angle.

 

[Obsessed with Edges]

I've never liked the description 'convex edge'. To me, I think it leads some astray in assuming the convex needs to go all the way to the edge, which is never a good thing. Any edge that's going to be sharp still needs to be formed by two intersecting FLAT bevels, even if those 'bevels' only comprise a teeny-tiny portion of the edge grind, with everything behind them being gradually radiused into a convex, leaving no obvious, discernable 'shoulders' to the edge 'bevels'.

When I started 'convexing', I was doing so with some conformable backing (leather) under sandpaper. I can see justification for setting up the 'behind-the-edge' portions this way; especially on very large & thick blades. It's easier to make a broad convex this way, and finishes up looking quite nice, even in relatively inexperienced hands. When it comes to working the edge itself and producing a crisp & sharp apex, transitioning to something much firmer or hard is definitely the better way to go. I sort of migrated unintentionally into doing it that way anyway, in that I was always finishing up by flipping my leather-on-oak strop block over, to the bare 'back side', and using the sandpaper over that to get the edge as crisp & sharp as possible. And that eventually led me to doing the whole thing on hard hones/stones. I didn't fully realize at the time, that this was the better way to go anyway; but, in retrospect, it now seems obvious.


David

 

[ToddS]

....
Convex edges accomplished on a soft surface, mouse pad or slack belt, are convex from the rounded shoulders clear through the apex; ...

There is a compromise if we only use sub-micron abrasives where the metal removal rate is too slow to produce any appreciable convexity.
In this case only the very apex is convexed (or micro-convexed) - improving keenness without altering the bevel profile appreciably - the big advantage being the "forgiving" nature of compressible or slack strops ensures the apex makes contact with the abrasive.

 

[Joe_Lane]

There is a compromise if we only use sub-micron abrasives where the metal removal rate is too slow to produce any appreciable convexity.
In this case only the very apex is convexed (or micro-convexed) - improving keenness without altering the bevel profile appreciably - the big advantage being the "forgiving" nature of compressible or slack strops ensures the apex makes contact with the abrasive.

What's your thoughts on using sandpaper on hard backed leather? Ever done any micrograph work?

 

[ToddS]

What's your thoughts on using sandpaper on hard backed leather? Ever done any micrograph work?

The closest I have come this this would be lapping film on wet paper - the result is, as expected, convexity for the larger grits, micro-convexity for the finer grits.