Mike Stewart: Convexed blades with convexed edges hold an edge much longer!

FortyTwoBlades said:
If the edge angle is equal, then the convex bevel will go visually higher on the blade stock than the "V" edge of equal angle. If the visual bevel width is held constant (which would be silly because it's just a cosmetic effect of imposing certain angles or arcs onto a given piece of stock) then the convex would be thicker but also have a thicker edge angle as a result.

If you were to impose a 15° per side bevel onto a 1/4" thick piece of stock it will look wider than that same 15° per side bevel on 1/8" stock. Fun fact: a BK-16 and BK-2 both have the same primary grind angle (unless they've changed something since the last time I measured it.) The BK-16 is a full flat grind merely because it is narrower than the BK-2, which is a saber grind only because it is so broad. And if the BK-16's blade were widened to equal that of the BK-2, that grind would stop much lower on the blade because the stock is thinner. However, at least up to that depth on both knives the cutting performance is equal. Yet most folks will tell you that the BK-16 is a thinner grind because of its stock thickness being lower and it being a full flat grind instead of a saber grind, which people automatically think is thicker. This is similar to the problems revolving around popular concepts of convex edges, or why people think scandi grinds are such good slicers when they're actually the thickest geometry you can have for a given stock thickness and edge angle (it's just thin stock and a really low edge angle.)
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I will have to digest what u wrote when I am on my computer and not on this cell phone.
 
marcinek said:
No! No! Its a counterintuitive concept. In fact for the same edge angle, HOLLOW has the most material behind the edge...

AND...I feel convex is "better" than vee too, but only because it is easier to maintain.
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Ok, now u have just ef'd me up with that hollow ground statement. Jeezus
 
As much bullshit as there is in the marketing, I like Bark River's knives and have several. The grinds are great for what I need to cut (wood and game). Weird company, but I like the product.

I just don't need any bizarre unprovable claims.
 
But bizarre unprovable claims are the foundation of commerce! Fiskars 28" Chopping Axe does so cut "three times deeper." :grumpy:

Next thing you'll claim nothing is free. :o
 
Cobalt said:
Ok, now u have just ef'd me up with that hollow ground statement. Jeezus
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It did the same to me. On the left diagram, the hollow curves would be outside the green ones. For the same edge angle (tangents) hollow is thickest.

The point is that a convex grind almost always has a more obtuse angle, so we think its "thicker." And hollow/concave have more acute angles and are thinner.

But, thickness/material behind the edge for a given angle is the exact opposite. Thats the bugbear.
 
Thomas Linton said:
But bizarre unprovable claims are the foundation of commerce! Fiskars 28" Chopping Axe does so cut "three times deeper." :grumpy:

Next thing you'll claim nothing is free. :o
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Even more powerful is convincing people that something easily demonstrable is NOT true. It takes a genius marketer to do that. Powerful stuff if one can do it.
 
grinds_zpsactzzxpo.png
 
Someone once told me that after enough sharpening most blades take on a convex edge. Any truth to this statement?


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Japanese katanas look flat ground, but I've been told from a reliable source that they are actually convex.
 
Natlek said:
Be my guest, draw a convex with this dimension of V edge :)

mshwg6.png
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Lemme talk it. It would be two curves, outside the red lines joining the point to the ends of the horizontal line.

And it would have a more obtuse edge angle than the vee grind shown by the red lines.

A vee grind with THE SAME edge angle as the convex would be "wider" than that convex, and have more material bejind the edge.

You can draw that convex if you like...it will demonstrate my point.
 
It does last longer. It is not because of there being more steel behind the edges either. The fact that there is more steel behind the edge, helps protect the edge from getting waves and deep chips in it.

The reason that the convex edge lasts longer, is because it engages the material far less than a straight edge. The curve of the convex acts like shoulders, pushing material to the side, and reducing the pressure, and amount of contact at the point of the edge.


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jeremy1517 said:
Someone once told me that after enough sharpening most blades take on a convex edge. Any truth to this statement?


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If you are using a stone freehand you are creating a series of microbevels. You csn hold your knife angle constant from stroke to stroke, let alone from session to session.

That series of flats/bevels tends toward a smooth curve. Thats why convex sharpening is so easy...it takes advantage of not being able to maintain a constant angle.

I think its why people ascribe magical powers that defy mathematics to their convex knives...they are finally able to get a good edge!
 
Cobalt said:
Squishy? Interesting word from someone with 80 posts. Troll
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Oh, please STFU. Having 14,152 posts isn't an indicator for competence, as everyone can see.

jeremy1517 said:
Someone once told me that after enough sharpening most blades take on a convex edge. Any truth to this statement?
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Yes, after enough stropping or freehand sharpening the ('shoulders' of the) secondary bevel will be 'convexed' bit by bit.
 
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That's right. The edge angle of a convex edge is the angle at very apex where the 2 curves meet. At the same apex angle, the convex edge will have less drag than a V edge from the bevel shoulders.
 
Convex edges are a perfectly normal V edge badly sharpened so that it is duller.

Manufacturers like Bark River Knives get around that by making the edge much thinner...


I can just see archaeologists in the future digging out one of our knives, and saying:

"Yes, despite the rust, you can still plainly see that this example has what was called then a "convex edge", typical of the early 2000 AD period. There was a mystical belief in that period that this type of edge made knives cut better: We never found any drawings of that time, all of them being on electronic support, and so of course long gone (which is what makes this period so fascinating and obscure to us), but we suspect all these drawings showed the convex lines drawn inside the V edge to support and perpetuate this mystical notion..."

Gaston
 
Stuart's marketing has done more to confuse convex edge and grind than anyone I can remember.

Convex edges don't hold an edge longer. His convex blades are not thicker than his flat grinding. He says they start as flat grinds, then are convexed with a grinder. The only way to do that is to remove metal, this it has to be thinner than the flat grind being replaced. This discussion cannot resolved without dimensions. I have reground hollow grind into flat grinds and finished off with the same edge angle as the original hollow grind. Several dimensions have to be given to make a meaningful comparison.
 
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