knives with "great geometry", and not so great geometry

7

72jroberts

Joined
Mar 16, 2012
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277
Some of the locals here that possess a lot of knife knowledge talk occasionally about "geometry" in relation to the cutting ability of the knife.
I think I may know what they- you- are talking about, but Im not quite sure.

Please list knives that have good/great geometry to you, and knives that have not-so-good geometry.

If a knife has good geometry, does it mean that it has a delicate blade, or are there some thick .25 inch knives that have good geometry?

Thanks for your considerations,

John
 
The real question is, good geometry for what? Slicing? Stabbing? Chopping? Etc.

In general, good geometry for an edc blade means thin enough behind the edge for slicing, as well as a certain level of thickness for strength. This can be achieved a number of ways. Take for example the spyderco techno and the benchmade 940. The techno has a very thick blade at the spine, especially for its size, but because the blade is wide from spine to edge, the blade becomes quite thin just behind the edge while still being stout due to the thick blade stock. The 940 on the other hand, has a much more slender blade from spine to edge and much thinner blade stock. The thin, slender blade make it a good cutter, but the reverse tanto blade shape and saber grind help retain strength. Both are very different but very good approaches to edge geometry for an edc blade.

There are of course many other applications of knives, and different applications require different geometries. A chef's knife for example needs to be absolutely as thin as possible behind the edge and maintain much of that thinness all the way to the spine in order to maximize cutting performance with little regard to strength.

A big, heavy chopper on the other hand is going to benefit from a thicker blade stock for strength combine many times with a convex edge, again for strength as well as for the properties a convex edge has when going through a hard material. A thick stock with a convex edge will tend to split hard materials rather than wedge into them.

Again, it all depends on the knife's intended purpose as well as the performance requirements of its user.
 
Good blade geometry= Opinel no. 6.

Yes the stock is 1/16", but seriously, unless you're using the knife as a prybar, it's not going to break. They have been used for how many years as farm and peasant knives?
 
The best all around geometry that I know of is the Microtech Socom Elite. It's super thin shoulder effortlessly push cuts through the toughest materials. I was push cutting some 1/2 thick Buna N oring seals that wthstand over 30,000 psi & it went through with very little force compared to an Umnumzaan, Para 2, Manix 2, XM-18 slicer. The blade stock is very thick with a strong tip that can penetrate very well. it's IMO the best all around geometry that I know of. If you wan't the strongest tip strength possible the XM-18 Spanto is the most robust I've ever seen.
 
i find my ZT 560 perfect for me, not too thin but more than thick enough for EDC, a good reinforced tip and a good blade steel make it perfect imo.
 
Personally these knives I found they have perfect geometry. When they lands in my hand, just feel perfect and they are from the same family.
Darrel Ralph Gunhammer, Darrel Ralph Trigger, Combat Elite RRF. Personally, I would say RRF is designed by Darrel. I seriously can't see much of Wilson touch on the design. Trigger and RRF are very very similar geometry.
Gunhammer is also as perfect palm feel as it gets on a larger size folder.

Personally, like the geometry on above 3 over Sebenza. Sebenza is a bit too rigid in design. Handling both at the same time Darrel's design seems to be curved at right places. feel comfort and your hand seems naturally wrap on.
I love Darrel's design a lot. So far, I have not found another folder designer's work touched me as much.

As for fixed blade with good geometry, BUSSE Combat. I've not found a BUSSE that wasn't fall in love at first touch. These guys are amazing.
 
Thin cuts.

Thick will cut too, but it requires altering your technique.

For example, my Dozier's, I have one custom, and one of Kabar's Dozier designed blades, both have a wicked deep hollow grind, and when cutting media, you have to "reign" in the blade, as it wants to bite deeper than you may be willing to go.

Are there thick knives, that have good geometry for cutting, yeah, there are. This one is my favorite,

100_1228.jpg


To get a thin edge on a thick knife, you need blade height real estate, the shorter the blade, the thicker the edge will be. My BK2 is a full .250 in thick, but with a good edge it will perform much better than many think possible. This edge is 50 degree inclusive, which, according to most, is a rather obtuse edge. I agree, but its thin enough to do what you saw in the picture, but thick enough to withstand impact with the full blade weight behind it. My BK2 is a rough use knife, so, the edge I have on it, is there to facilitate my treatment of the knife.

My custom Dozier, is not a rough use knife, has a whisper thin edge, and will cut meat so thin, it only has one side.

Edge geometry is everything in a blade.

Moose
 
Although this is a kitchen knife picture, its easier to show as an example because you can see the geometry from spine to edge.

This beast is over 4mm thick at the spine, but it tapers so beautifully all the way down (the picture doesn't even show how thin the last 2mm are right above the cutting edge). Let's just say that this thing makes effortless cuts on 95% of food material...perfect for its intended purpose.

Not all knives would benefit from this particular geometry, especially a hard-use blade. Hope this helps to show what people mean when referring to good/bad geometry for a knife's intended purpose.

mvi87o.jpg

9v874i.jpg
 
jimnolimit said:
^ ding ding ding.

"good" geometry is a relative term.
Click to expand...

+1. A hatchet has great geometry for chopping wood. It has terrible geometry for slicing a tomato.

And, as Moose45 so elequently noted, a thick spine or large edge angle does not necessarily mean "bad slicer." Rapid increase in thickess from edge "width" to spine width is what negatively affects slicing (and helps chopping/smashing/bashing). Gradual increase in blade thickness from edge "width" to spine width (which demands that "blade height real estate") is what makes a great slicer.

That's what "geometry" means.
 
mkjellgren said:
The real question is, good geometry for what? Slicing? Stabbing? Chopping? Etc.

In general, good geometry for an edc blade means thin enough behind the edge for slicing, as well as a certain level of thickness for strength. This can be achieved a number of ways. Take for example the spyderco techno and the benchmade 940. The techno has a very thick blade at the spine, especially for its size, but because the blade is wide from spine to edge, the blade becomes quite thin just behind the edge while still being stout due to the thick blade stock. The 940 on the other hand, has a much more slender blade from spine to edge and much thinner blade stock. The thin, slender blade make it a good cutter, but the reverse tanto blade shape and saber grind help retain strength. Both are very different but very good approaches to edge geometry for an edc blade.

There are of course many other applications of knives, and different applications require different geometries. A chef's knife for example needs to be absolutely as thin as possible behind the edge and maintain much of that thinness all the way to the spine in order to maximize cutting performance with little regard to strength.

A big, heavy chopper on the other hand is going to benefit from a thicker blade stock for strength combine many times with a convex edge, again for strength as well as for the properties a convex edge has when going through a hard material. A thick stock with a convex edge will tend to split hard materials rather than wedge into them.

Again, it all depends on the knife's intended purpose as well as the performance requirements of its user.
Click to expand...

jimnolimit said:
^ ding ding ding.

"good" geometry is a relative term.
Click to expand...

Moosez45 said:
Thin cuts.

Thick will cut too, but it requires altering your technique.

For example, my Dozier's, I have one custom, and one of Kabar's Dozier designed blades, both have a wicked deep hollow grind, and when cutting media, you have to "reign" in the blade, as it wants to bite deeper than you may be willing to go.

Are there thick knives, that have good geometry for cutting, yeah, there are. This one is my favorite,

100_1228.jpg


To get a thin edge on a thick knife, you need blade height real estate, the shorter the blade, the thicker the edge will be. My BK2 is a full .250 in thick, but with a good edge it will perform much better than many think possible. This edge is 50 degree inclusive, which, according to most, is a rather obtuse edge. I agree, but its thin enough to do what you saw in the picture, but thick enough to withstand impact with the full blade weight behind it. My BK2 is a rough use knife, so, the edge I have on it, is there to facilitate my treatment of the knife.

My custom Dozier, is not a rough use knife, has a whisper thin edge, and will cut meat so thin, it only has one side.

Edge geometry is everything in a blade.

Moose
Click to expand...

^Quoted for truth. Excellent posts, guys. Context is EVERYTHING in determining appropriate geometry.

The ideal cross-sectional geometry for a knife (as a gross generalization) is going to give you the thinnest edge it can without compromising required strength, and will minimize the volume that must be displaced by the blade as it passes through the intended range of cutting mediums. Thickness will only be as much as is necessary to withstand the forces of typical use, plus a reasonable additional margin for accidental stresses. Grind geometry should take medium binding into account if it will be used for cutting springy or resistant materials. Whether the blade will be used for slicing or percussive cutting (chopping) should also be taken into consideration. Profile should be idealized to concentrate mass where it will be most useful and lend appropriate balance while presenting the edge to the intended targets in a manner appropriate for its intended tasks. The shape of the tip should likewise be designed with intended uses in mind.

Just some of my observations on the topic, though I'm not infallible.
 
Good low price examples are CS Large Voyager (clip or vaquero) for tactical/modern folders and Victorinox chef and paring knives for kitchen blades. They have better blade geometry than majority of their competitors that cost much, much more.
 
Moosez45, if you go below 50 degree, do you start to see damage to the edge?
 
I have a Socom Elite in 204P. For a good slicer/cutter it is hard to beat. 5mm at the spine and a half mm or so behind the edge. It makes my Delica seem like Fat ASH. The Socom is a better cutter/slicer that most other knives that pass for having a thin edge while having a 0.1969" spine.

But it also depends on your cutting medium. It may be ground super thin at the edge, but the spine is thick enough that it may hang up when cutting apples and whatnot.
 
Transition from main grind to edge dictates good geometry. They have to blend almost as one. Thickness behind the cutting edge is also important.
Scott
 
me2 said:
Moosez45, if you go below 50 degree, do you start to see damage to the edge?
Click to expand...

I've run one down to as low as 30 degrees inclusive once, you would see some rolls after cross grain batonning, nothing heavy, but my BK2 is thoroughbred workhorse, I prefer it to be 50 degrees inclusive.

40 would work just fine as well.


FortyTwoBlades said:
I bet it could take a 30 degree just fine, personally. :)
Click to expand...

Done it, works. Shave like a Gillette. I did get a few small rolls though.

Moose
 
Moosez45 said:
Done it, works. Shave like a Gillette. I did get a few small rolls though.

Moose
Click to expand...

That's why personally, I'd rather have a super shallow hollow grind or a wide FFG with a 40 degree or so edge, than a thick meaty blade with a 30 degree edge.

Edge geometry is important, but so is the grind and how it tapers.
 
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