Flat vs hollow (again)

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Sebrw

Joined
Oct 2, 2019
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Hi!

I know that this question has been reviewed many times and I spent countless time reading about it but my own experience makes me confused.
For what I read, the general consensus is that hollow ground blades makes better slicers and flat ground blades better "cutter" (meaning deep cut).

My two favorite EDCs are a case large stockman (6375) (hollow on all blades) and a victorinox pioneer x (flat ground blade).

After various tests (bread, meat, dry sausage, tomato, cucumber, wood, paper, whole post-it block, cardboard, plastics, rubber...) I found that the flat ground blade of my victorinox performs better on all material tested, doesnt matter if I slice or cut.

I was even more confused after the last test (cutting through a whole post-it block) because before the test my stockman was hair shaving sharp while the pioneer was just sharp (cut easily through paper but not hair shaving) but the pioneer anyway went through the paperblock like butter while I had to apply considerable pressure on my stockman.

I believe the steel is not the issue as I read that case truesharp and victorinox stainless are roughly similar in term of performance.

So does blade geometry really explain these results or do I just suck sharpening hollow blades?

Thanks!
 
You shall take into consideration at least:
1. The thickness behind the edge
2. The blade thickness
3. The grind geometry

For sure other factors are involved but for keep it simple these 3 factors are imho the first ones to take into account

for most EDC tasks the thinner the blade is behind the edge the better it is
Blade geometry will only be second

all things being equals i usually prefer hollow grind
 
Thanks for your answer.

1- hollow blade of the stockman is thinner right behind the edge
2- Blade Thickness: Pioneer (2.6mm) > Stockman (2mm)
3- Flat for Pioneer, hollow for stockman

Following your reasoning, the stockman should be better...
 
Sebrw said:
Thanks for your answer.

1- hollow blade of the stockman is thinner right behind the edge
2- Blade Thickness: Pioneer (2.6mm) > Stockman (2mm)
3- Flat for Pioneer, hollow for stockman

Following your reasoning, the stockman should be better...
Click to expand...
Yes that is what I would have expected

I will do some tests with some of my Victorinox , you have made me curious ;)
 
All hollow grinds will have a shoulder and will start to wedge once the cut is deep enough. The advantage here is that initiating the cut is easier, so once a knife starts to dull a hollow grind keeps it cutting just a little longer. The problem here is that the blade width on the stockman pattern is not enough to offset the thickness of the blade, so the shouldering effect is pronounced. People tend to pry with them anyways so lateral strength is a plus for the general public, just not for the enthusiast.

I prefer flat grind but will and do carry hollow grinds, so long as the blade stock is thin enough for the width of the blade.
 
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Do you know for certain that the edges on both identical? Even if one feels more sharp than another, the actual angle of the edge will make a difference.
 
I would like to test it out myself.

I have a full flat grind blade and hollow grind blade. Both 5mm thick, but different lenght, width, type (one is drop point and other one is tanto) and different steel (52100 and SK-5).

So testing it out would not make a lot of sense because of all these different factors playing role in it.

Having 2 same knives out of same steel with equal heat treat, just with different grinds would be ideal.
 
sharp_edge said:
For shallow cutting (i.e., not requiring the use of the entire blade height), hollow grind wins. Otherwise, FFG all the way.
Click to expand...

zD1DSn3.png


For the same edge angle: Green - hollow; red - flat; blue - convex.

Funny part....but for the same edge angle....thickest behind the edge is hollow. Geometry does not lie.
 
abcdef said:
Razor blades are thin from edge to spine - good slicers.

Sledge hammers - bad slicers.
Click to expand...
Traditional razor blades are not thin from edge to spine and are good slicers too. Geometry behind the edge is more important for pure slicing. Geometry higher on the blade is important when cutting something taller and what is best depends on what you cut. Try cutting a raw potato with a razor blade that is very thin edge to spine, or even with a FFG blade, not much fun, especially if you try to go fast.
 
ace said:
Traditional razor blades are not thin from edge to spine and are good slicers too. Geometry behind the edge is more important for pure slicing. Geometry higher on the blade is important when cutting something taller and what is best depends on what you cut. Try cutting a raw potato with a razor blade that is very thin edge to spine, or even with a FFG blade, not much fun, especially if you try to go fast.
Click to expand...

FFG chef's knives slice raw potatoes great.

Try cutting a raw potato or carrot with a Mora, which gets thicker quicker than a FFG. It splits them like a wedge.

 
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if the grind is a full hollow grind, usually it can be thinner than a full flat grind for the same blade thickness and height

if the primary grind stop at some point and doesn’t go to the full height of the blade it can be different for sure

by the way the edge angle is different than the grind of the blade, but can be limited by it
 
Sebrw said:
Thanks for your answer.

1- hollow blade of the stockman is thinner right behind the edge
2- Blade Thickness: Pioneer (2.6mm) > Stockman (2mm)
3- Flat for Pioneer, hollow for stockman

Following your reasoning, the stockman should be better...
Click to expand...
Geometry, specifically how thin the blade is at a given depth of cutting, dictates the ease of cutting per principles of mechanical advantage.

We don't have the measurements of your blades' edge angles and blade heights, but your assertions that the stockman is thinner behind the edge (i.e. at the shoulder of the edge bevel, typically 1/16" back from the apex) as well as thinner at the spine would indicate that it is a (slightly) thinner blade all though even before accounting for hollow grind.
I suspect that either a) the edge of the stockman is much less acute than that of the pioneer or b) your BTE measurement is incorrect. For some of the cutting, a toothy edge would work better than a smooth finish, but that is another matter.

Care to post images of the blades in question?
 
marcinek said:
FFG chef's knives slice raw potatoes great.

Try cutting a raw potato or carrot with a Mora, which gets thicker quicker than a FFG. It splits them like a wedge.

Click to expand...

Really FFG chef knives are great at cutting raw potatoes fast, this I want to see. See how garlic gets stuck to the razor blade and he has to push it off with a finger. This is exactly what happens with potatoes, but on a larger scale. Best performing chef knives are not FFG, usually some type of convex or some other complex grind. FFG is very good at cutting hard, non sticky things.
 
Not sure of your pioneer, but my SAK pioneer spear blade, in addition to the flat grind, also shows distal taper from heel to point. I find the first 1/2 cuts better than if utilizing the whole blade length.

I have similar length slipjoints that slice better, but they are thinner behind the edge, and less thick at the spine.

I think the case blades I have are flat, rather than hollow. The only hollow ground case I had was a medium stockman I gifted to my wife's father.
 
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Given a certain fixed spine thickness and blade width, a full height hollow grind (rarely seen outside of multi-bladed traditional folders, but Douk-Douks are one example) allow for an overall thinner blade geometry behind the edge bevel without a large reduction in rigidity. This is the reason why hollow grinds are so often seen on traditional folders. Their very small and narrow blades have to balance rigidity vs. cutting ability, and because rigidity scales cubically with thickness (which is why I beams are so effective), having a full height hollow grind allows them to be "thick" at the spine for requisite rigidity while being thin through most of the blade. The closer to the apex of the edge you get, the greater the order of magnitude of influence specific geometry has on cutting performance. So consider these variables when it comes to how one would optimize the overall performance of a particular blade within its context of use. Essentially the narrower the blade becomes, the thicker the grind angle will end up being in a FFG if stock thickness is held constant, so hollowing allows you to "scoop" more steel out to reduce the thickness behind the edge while maintaining a given spine thickness. The usual issue with hollow grinds is that depending on how they're done, the transition into the spine can end up becoming abrupt enough that it causes truly significant binding in a cut. So the specific curve to the hollowing matters, as well. In general a smooth and gradual hollowing rather than an abrupt one will provide the best overall performance if hollowing is determined to be a desirable trait for the particular knife.
 
M marcinek You seem to be obsessed with geometry at the very edge. This is a numeric value, and just that. It doesn't translate this way in reality. In my experience, it just doesn't work that way. I admit "through cutting" is done easier with a FFG blade or even a flat blade with a short keen edge (imagine an Old Hickory butcher blade (my best cardboard cutter, by the way). In everyday tasks, hollow ground blades fare just brilliantly. They are often as good, or better slicers. And keep a stronger spine... Just in case you need to pry open a door or a manhole. You know, survival !
 
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herisson said:
M marcinek You seem to be obsessed with geometry at the very edge. This is a numeric value, and just that. It doesn't translate this way in reality.
Click to expand...

I would say other are obsessed with geometry "behind the edge". :D Never really got "how far behind the edge" that means. I thing "far enough behind to back up one's argument."

Admittedly I am obsessed with comparing apples to apples with geometry and slicing, and I do think the only way to do that is to compare matching edge angles.

But it is a rabbit hole. Even gives me a headache.
 
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