Pros and cons of Hollow grind?

Excuse me, but I believe the term "BITE ME" fits in here. :eek: ;) The OP asked for pros and cons; pro-slices well; con-brings up comparisons which drive (or short walk) to insanity. :p
 
Wowbagger said:
I've always thought in the back of my mind that a hollow grind could be a self jigging knife for sharpening. Though I have never tried it. Picture how a razor is like this.

In theory one can plunk the knife down flat on the stone with the spine riding on one side and the sharpening bevel riding on the other side and just run the knife on the stone until it is apexed. Now a razor gets more complicated (as I understand it I have never sharpened a razor) in that one only uses the stone so far on a razor and stops short of apexing or a bur in any case and then go to the strop for the final edge.

Anybody sharpen their robust hollow ground EDC this way or is this pure fantasy on my part ? ? ? ?
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Some folks in the green woodworking world who make a lot of their own carving tools like to make their sloyd knives with a hollow grind and then hone as a flat over it. Sort of a hollow scandi, as it were.
 
mtngunr said:
If you look up Chris Reeve videos, he does an excellent explanation of what is good about them, why he made his knives the way he did, and does....
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I use my folding knives in the kitchen, and KNOW that my large Sebenza (hollow ground) will out-slice anything I put in front of it...including any flat-ground blade of the same spine thickness and similar BTE measurement.
There just is NO CONTEST...in my opinion...
 
Wowbagger said:
In theory one can plunk the knife down flat on the stone with the spine riding on one side and the sharpening bevel riding on the other side and just run the knife on the stone until it is apexed. Now a razor gets more complicated (as I understand it I have never sharpened a razor) in that one only uses the stone so far on a razor and stops short of apexing or a bur in any case and then go to the strop for the final edge.
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A razor is no more complicated. If you don't mind scratching/polishing the spine (most people don't, some do and cover it with a piece of tape) you just put the whole thing on the hone and go to town with whatever voodoo progression you prefer (4k/12k for me). Once it'll shave you hit the strop until it's comfortable, if it's not comfy, use a loaded strop, then strop before shaving.
 
pinnah said:
I would be surprised if any real empirical study on this exists. The common test for edge retention is CARTA gel, which is too soft to cause the wedging issue and realistically only tests for edge retention at or near the cutting edge - which is to say, that hollow grinds actually have the advantage.

I have 3 Buck 110s. An old one from the seventies with a semi-hollow grind and rounded shoulders (more costly to produce). And I have 2 current models with a more traditional deep hollow grind and a very pronounced shoulder. One of these newer 110s, I put it to a course stone and I flattened off the the shoulders of the hollow grind.

It's almost immediately apparent when slicing up a few pounds of potatoes and rotating between the knives. The modern 110s make the initial cut much easier because they are thinner behind the edge (the old semi-hollow grind is actually thicker above the edge) but the old 110 and the modified new 110 slice all the way through the potatoes much more easily. There is considerably less drag.

Similarly, I had a Mora Companion HD that I convexed and it out battons my hollow grind Buck Reaper. Same thing. The should of the hollow grind binds up whereas the appleseed profile of the convexed Mora splits and goes through the wood faster. Again, side by side comparison of knives helps illuminate that.

NOTE: I'm not saying that you can't slice potatoes or split wood with hollow grinds. Obviously, you can.
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I believe that convexing would help that issue. Then again, convexing is only further removing material from a relatively thin grind, which is obviously not going to hurt.

I would like to see someone demonstrate that, given identical edge thickness, stock thickness, and bevel height, there exists a material that would be displaced easier with a flat ground blade than with the equivalent hollow ground one. In other words, show a material that would bind harder against the shoulder of a hollow grind than against the entire flat surface of the flat ground blade, which is thicker in all locations leading up to the shoulder. I have some doubts that such a cutting medium exists.
 
Yeah, you can have a very thin and sharp edge section and a nice and thick spine even on a relatively narrow blade. The Buck 110 is a prime example of that.
 
Hang ups (or so I hear) happen in hard cutting and chopping work. Chop a hollow-ground bowie onto a carcass and the blade brakes when it goes through bone and cartilage. That's what they all claim. As a slicer, it's neat since the blade is thin right at the edge and sharpening it easy: just lay it flat on the stone.
 
marrenmiller said:
I would like to see someone demonstrate that, given identical edge thickness, stock thickness, and bevel height, there exists a material that would be displaced easier with a flat ground blade than with the equivalent hollow ground one. In other words, show a material that would bind harder against the shoulder of a hollow grind than against the entire flat surface of the flat ground blade, which is thicker in all locations leading up to the shoulder. I have some doubts that such a cutting medium exists.
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Hey Marley,

I believe there are 2 issues. First, a hollow grind is thicker above the grind line compared to an otherwise comparable full flat grind. This can be seen by drawing the profiles on paper and demonstrated by placing a hollow grind flat on a stone and scrubbing down the shoulder to flatten it up to the spine. I've done it on numerous occasions and it takes some time and elbow grease. It's a process that removes a good amount of metal. As noted, I've done this with 2 Buck 110s with otherwise identical blades. The difference is very noticeable. Returning to a simple line drawing comparing a full flat grind and a hollow grind with similar spine thicknesses, when cutting difficult to separate mediums (potatoes, yams) the hollow grind is effectively a shorter wedge, thus creating a wider wedging angle.

The second issue I believe is the sharpness of the grind line. Again, using newer Buck 110 side by each with an older Buck 110 is telling. While both have the same height of the hollow grind, the newer knives have a very distinct and sharp shoulder while the older ones were made with a convexed transition. The drag on the sharp shoulder is definitely something I can feel when cutting potatoes, yams and squash. YMMV.


Hope this helps
 
It is easier for me to sharpen a hollow grind without scratching the sides of the blade. I scratch flat ones every time.
 
pinnah said:
Hey Marley,

I believe there are 2 issues. First, a hollow grind is thicker above the grind line compared to an otherwise comparable full flat grind. This can be seen by drawing the profiles on paper and demonstrated by placing a hollow grind flat on a stone and scrubbing down the shoulder to flatten it up to the spine. I've done it on numerous occasions and it takes some time and elbow grease. It's a process that removes a good amount of metal. As noted, I've done this with 2 Buck 110s with otherwise identical blades. The difference is very noticeable. Returning to a simple line drawing comparing a full flat grind and a hollow grind with similar spine thicknesses, when cutting difficult to separate mediums (potatoes, yams) the hollow grind is effectively a shorter wedge, thus creating a wider wedging angle.

The second issue I believe is the sharpness of the grind line. Again, using newer Buck 110 side by each with an older Buck 110 is telling. While both have the same height of the hollow grind, the newer knives have a very distinct and sharp shoulder while the older ones were made with a convexed transition. The drag on the sharp shoulder is definitely something I can feel when cutting potatoes, yams and squash. YMMV.


Hope this helps
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A full hollow is thinner at all points than a full flat, and a saber hollow of the same height is thinner than a saber flat at all points. I'm talking about equivalent grinds, not a full flat vs saber hollow. Otherwise the comparison would be apples to oranges. Your description of flattening out a hollow grind serves to compare two dissimilar grinds, not equivalent ones.

As for the shoulder of a hollow being sharp: yes, it is more acute of an angle. My question is, does that oppose displacement more than the entire primary bevel of a flat grind, which is thicker the whole time between the edge and the shoulder? I've never seen any wedging like you are describing.

Once again with the convexing, the moment you convex the shoulder, you are removing metal. That is not a valid comparison if the older bucks have less metal at the shoulder.
 
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Visual bevel width should not be used as a comparison of geometry because it's a visual artifact of a given geometry being imposed on a given stock thickness. Stock thickness/width, specific geometry, and edge angle need to be held constant, but not visual bevel width. When dictating convex and concave geometries it can be difficult to make comparisons to flats since there's so many possible variations. Not all hollows or convexes follow a simple radius.
 
FortyTwoBlades FortyTwoBlades makes an excellent point. The wheel that provides the concavity during grinding is a constant (diameter). The shape of the blade is not.

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Full hollow on an eight inch wheel, 5/8" tall blade.

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3/4" tall blade done on same wheel.

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1 1/16" tall blade on same wheel. All are slicey but the geometry is different.
 
CATRA is a wonderful, quite relative way of testing knives for a relative cutting ability index, all quite divorced from the fact that the world is not made of dirty cardboard.

HOWEVER, knife manufacturers examined spoiled cubical dweller western knife buyer knife uses for paper cutting and kitchen, only, factored in that what passed for skilled blue collar today is a warehouse job, and multiplied by a factor of 10 the idea cutting cards would be a nice cheap standardized test, ..

And, we have, tah dah, CATRA...which is a PERFECT way of rating knives for those whose worlds are made of cardboard...

However, for the rest of us, it gives us flexing chef knives marketed as police and military, blades which will snap when stabbed into something involving maybe buckles, buttons, snaps and bone, and which protruding broken chunk likely to amputate stabbing fingers...

Hollow ground can have its uses...so can others....
 
FortyTwoBlades said:
Visual bevel width should not be used as a comparison of geometry because it's a visual artifact of a given geometry being imposed on a given stock thickness. Stock thickness/width, specific geometry, and edge angle need to be held constant, but not visual bevel width. When dictating convex and concave geometries it can be difficult to make comparisons to flats since there's so many possible variations. Not all hollows or convexes follow a simple radius.
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It can be used for comparing to a flat grind with otherwise identical primary bevel height, stock width and thickness, and edge thickness. That's all I'm getting at.
 
Yeah, but what I'm saying is that it's a cosmetic artifact that has little meaning in the context of evaluation. It's a symptom rather than the cause, if that makes sense. If you keep bevel height identical, it makes convex geometries thickest, flats in the middle, and hollows thinnest. But if you were to keep the thickness of the edge shoulder constant instead, and instead look at the bevel geometry as if it's a graph of how quickly the blade reaches full stock thickness as you travel from the edge shoulder toward the spine it paints a much more useful picture.

As a general rule, though, full height grinds of any type tend to be a better option than ones that aren't.
 
FortyTwoBlades said:
If you keep bevel height identical, it makes convex geometries thickest, flats in the middle, and hollows thinnest.
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This is all I'm getting at.

Nobody grinds a blade with consideration to thicknesses at given points, but instead as a function of blade stock, blank profile, and bevel height (at least, that's what I do and what it seems most people do when physically making a knife). The theoretical question is: all other blade features being identical, does a hollow grind cut better than a flat grind? Or, if I take a given blade blank and do a comparable height grind with hollow or flat, then which cuts better? That question only makes sense if all other components are identical, and thus comparing with the bevel height is totally fine in this theoretical case.

Otherwise, this just devolves to the convex/flat grind argument all over again in different form.
 
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