What is the toughest type of knife grind?

Sticking with math and geometry, if you decrease the inclusive angle of the flat edge to 45 deg, the convex edge will be outside the flat near the edge.
 
hermit dave said:
Sticking with math and geometry, if you decrease the inclusive angle of the flat edge to 45 deg, the convex edge will be outside the flat near the edge.
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You don't seem to understand that both have an identical angle at the apex. Reduce one without reducing the other and you're not making a valid comparison. Edge angle must be held constant for the basis of comparing geometry in this circumstance.
 
Out of curiosity, where do chisel grinds (like the ones on Emerson knives) fall with respect to toughness?
 
The starting point of the radius, the size of the radius, and the angle of the arc can be measured, but you can't compare it to the linear angle of a flat edge.
 
Dadpool said:
Out of curiosity, where do chisel grinds (like the ones on Emerson knives) fall with respect to toughness?
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In theory it's no different than double bevels of equal angle. In reality, the asymmetry tends to cause unequal strain on the edge and makes it more prone towards rolling the apex.


hermit dave said:
The starting point of the radius, the size of the radius, and the angle of the arc can be measured, but you can't compare it to the linear angle of a flat edge.
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Actually, you can. Even cursory research will show this to be the case. You just use the tangents at the intersection.

Edit: Here's a video. :)

[video=youtube;Ni17rUS3IWo]https://www.youtube.com/watch?v=Ni17rUS3IWo[/video]
 
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The more steel behind the edge the tougher it is, so slab flat grind with a convex, moran, edge is toughest, given any one steel. Thing is that doesn't add strength to the blade, keenness to the cut, nor mass. Its a slab with a rounded edge. Lawn mower blades get that way,

Have thickness to the spine of the blade to give some lateral strength and mass. The grind whatever type is to taper down so a fine cutting edge can be made that is keen and allows the cut to go deeper.

If there isn't enough metal behind the edge then the blade can buckle behind the cutting surface due to being just not enough to handle all the forces. Kitchen knives are thin to be keen, cut deep, but can't take much force as there isn't enough metal. Axes aren't keen though can be sharp, and have loads of metal behind the cutting edge; they also chip out wood more so than cut, so a different technique.

The rest is makers using the grinds to either keep metal there or get a deeper keener cut. Its a compromise.

So the answer is the toughest grinds keep the most metal behind the cutting apex. A moran edge is strong and can cut and made when stropping as the leather strop is slack. Its not the sharpest keenest edge but more robust than so fine the edge becomes delicate.
 
GREENJACKET said:
The more steel behind the edge the tougher it is, so slab flat grind with a convex, moran, edge is toughest, given any one steel.
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But only if it has a more obtuse edge angle. And then, a flat with the same edge angle would have more steel behind the edge.
 
hermit dave said:
The convex edge has no angle. It's an arc.
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So when you are creating a convexed edge, the blade is held perpedicular to the abrasive? Thoats the only way to round it off.

Funny, I always thought the key factor in creating/sharpening convex edges was to NOT round off the edge.
 
marcinek said:
You and I go through this every time, don't we?
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I can understand why a lot of folks might think that it's not measurable, but it's as simple a matter as Googling "angle at intersection of curves" and you get about 8,610,000 results on the subject. :)
 
A straight line and a curved line are not the same thing. The angle of intersection and linear angle are not the same thing.
 
hermit dave said:
A straight line and a curved line are not the same thing.
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You do realize what the tangent vector represents, right?

Edit to add: Here you can see a tangent vector following a dot as it moves along a curve. At each point along this curve, the line segment is tangent to the curve.

Graph_of_sliding_derivative_line.gif
 
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FortyTwoBlades said:
I can understand why a lot of folks might think that it's not measurable, but it's as simple a matter as Googling "angle at intersection of curves" and you get about 8,610,000 results on the subject. :)
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Yup.

CurveAngleFig_zpskpdtdo75.gif


f1 and f2 are curves that meet at P. The tangent to f2 at P is t2. The tangent to f1 at P is t1. t1 and t2 meet at an angle that measures phi. That is how science and mathematics defines the angle the curves meet at.

I mean, I'm sorry if math ruins everybody's fun, but you cant say 2 + 2 = 5 or a pentagon has 8 sides if you don't like it.
 
Claiming you can measure the included angle of a convex edge is like saying you can measure 1 side of a sphere.
 
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