'Feel' of a convex edge

[SpookyPistolero]

Hi folks-

Just wanted to get y'alls thoughts on something. When I sharpen a flat grind or scandi to a 'sharp' edge, I can always tell. I usually tell by cutting a few things like paper, string, shaving, and by literally touching the edge with my fingers. Those all 'feel' sharp to me.

But with a convex edge, it'll often cut well and get hair-popping, but simply doesn't have a sharp feel to it when touched with a fingertip.

Anyone else notice this as a basic quality of convex edges? Or do you normally get that same 'edginess' out of one?

Just curious-

 

[richard j]

sometimes i can tell any difference but i think that depends on how dry my skin is. i seem to notice more bite if the skin on my fingertips is really dry. some of my chisel ground blades feel the same way. try feeling the blade from one side then the other and see if you notice a difference.

 

[Zeasor]

...But with a convex edge, it'll often cut well and get hair-popping, but simply doesn't have a sharp feel to it when touched with a fingertip.

Anyone else notice this as a basic quality of convex edges? Or do you normally get that same 'edginess' out of one?...

I don't notice any difference in the "edginess" feeling with a convex edge. Sometimes a "toothier" edge will feel sharper (the pointed teeth grab the skin more effectively). An edge with a remaining burr will feel different from one side to another.

 

[chuck buck]

as well as not feeling as sharp (when the finger is slid down the blade width) they often dont "look" as sharp as normally ground knives. i actually reground the edge on my brkt because it "felt" dull. i know i know.. ive changed my baby back to what she wanted to be all along.

 

[db]

You could be rounding the very edge off of your convex edge and/or polishing it more than your v edges. I don't notice any difference in bite between a convex edge and a v edge at the same grit finish. I even beleive after I've convexed my knives they cut better than they did with the v edge and blade grind it had.

 

[ss Dragonfly]

Convex bevels by nature have more steel behind the cutting edge. This could account for the "feeling" of not as sharp. Less sharp maybe a little, more durable definitely. Everything is a trade off, durability vs. toothy edge. Also, you may not polish your V grinds to the extent that you do for your convex edges. I theorize this may be the case since my convex edges are maintained on a strop...they see more of the strop just by the nature of the beast, Just Maybe............ BTW ,I love D2 convexed edges

 

[Lucky Bob]

Convex bevels by nature have more steel behind the cutting edge.

Assuming that both bevels terminate at the same included angle (and why bother comparing them if they don't?), then that is factually inaccurate. I just whipped this up in a CAD program, to illustrate the point:

They're both 40 degree edges on a 1/8 thick piece of material. There is visibly more material inside the V-bevel shape than there is inside the convex bevel.

 

[Zeasor]

Lucky Bob--- Perfect illustration of a good point.:thumbup::thumbup::thumbup:

 

[jaislandboy]

+1
thanks Lucky Bob :thumbup:

 

[ss Dragonfly]

If you will kindly look at this

http://swordforum.com/swords/nihonto/americanized.html

you will see what I mean...scroll down to cross section of blades and maybe try not to jump to conclusions...

 

[Lucky Bob]

I was going to take this to email/PM, but since both of yours are disabled, I'll do it here. I read the section you suggested. I fail to see its relevance. Yes, I agree that, from a wedging/"fluid"-dynamics point of view, a convex grind has several advantages over either a flat or concave grind. Yes, convex bevels will have a greater area behind/inside them than a highly concave grind.

That being said, however, the vast majority of blades, including the ones mentioned by the OP ("When I sharpen a flat grind or scandi to a 'sharp' edge, I can always tell"), have flat-ground bevels, not hollow. If we are to limit our comparison on flat versus convex, with equal edge angles, there just won't be as much metal behind the edge of the convex grind.

My understanding of this confusion is that when people convex an originally flat-ground blade, they edge up putting as much of the curvature near the edge as they do towards the flats (see attachment 1). This results in more metal immediately behind the edge, but that is simply a consequence of increasing the final angle. As an example of that, I copied the outline of the complex/convex Japanese grind from the link you sent me over the other symmetric profiles in that image. As you can see, although the convex grind has more material than most of the other grinds, it also has a significantly larger final angle. That is not to say that a more obtuse final angle is a bad thing, it's just DIFFERENT. You could obtain toughness by increasing the final angle on a flat grind, too.

Attachment 1: A slightly more complex version of my previous illustration. In this example, there are three curves: the two in the previous example (a flat/scandi grind of 40 degrees, and a convex grind which is tangent to the flats and terminates at the same angle as the scandi grind) and a new one, in which metal was "removed" from the edge as well as the shoulders in the process of convexing the knife. As you can see, it has more metal immediately behind the edge, as would be expected to accompany the increased angle.

Attachment 2: Visual overlay of the Japanese convex profile on top of the other supplied profiles. (Although the graphic illustrates the original authors point, the profiles have been left in their original, slightly inaccurate form.)

 

[ss Dragonfly]

Yes, I agree that, from a wedging/"fluid"-dynamics point of view, a convex grind has several advantages over either a flat or concave grind. Yes, convex bevels will have a greater area behind/inside them than a highly concave grind.......



I agree as well...........

All is good, just different...hmmm where have I heard that?

Happy cutting