A visual guide to Edge geometry vs Blade geometry

[Evil D]

Even a near zero grind with a razor sharp edge can't compensate for thick blade grind and thick blade stock.

Exhibit A.





It did fully make the cut but the end result wasn't pretty.



What you're seeing there is not actually a jagged cut, but the result of the blade spine wedging like a door stop and rippling the board as I forced it through the cut.


Now... before y'all start yelling at me, I am well aware that this is the worst way to cut a box, and I know that if you just angle the blade 45 degrees to the board it will cut significantly easier (and if you didn't know that, try it for yourself). But, let's just say you needed to make a nice square cut for your kid's science project poster board or something so you had to cut the board right at 90 degrees.

I also know that if I had use the tip, the cut would be much easier, and that proves the point I'm trying to illustrate because distal taper makes the blade much thinner towards the tip and that's why it cuts easier.

For reference this was one of the later Nilakka's that did come with a tiny little bevel, and I've sharpened it at 30 inclusive. The edge also got the crap dinged out of it when I finished the cut and banged the edge against the floor which is epoxy coated....which is why I really feel that S30V was not the best steel for this knife but I suppose technically that would have happened to any 30 inclusive edge on S30V.

I can only imagine what this knife would do with 1.5-2mm blade stock. I believe these were 4.5mm thick. I love this knife but even with being almost a zero grind, it doesn't slice like my 3mm regrind Manix 2 does. Sure, for softer materials and even rigid ones that are shorter in height, the Nilakka may show an advantage but the thickness does ramp up quickly around the center of the blade. I could measure later but I'm fairly certain that my Manix is significantly thinner at the same height from the edge than the Nilakka is.

Now imagine how all this compares to a common utility knife blade with how thin those are. This whole topic is basically about forcing a wedge shape through a material and at some point the sharpness of the leading edge can only do so much to make that action easier.


Anyway just something fun I thought we could chat about. I'm really curious about the HP Delica and how that blade is going to be ground. I will always love my Shaman and big beefy knives but the other end of the spectrum is sure a lot of fun to play with.

[Foehammer]

I love these kinds of threads! Thanks EvilD, you do a lot for this forum and are always willing to share your knowledge with us. Appreciate it!

[JSumm]

That's a great visual David. The Nilakka is definitely an homage to the Finnish Puukko with it's thick blade stock. Probably a great wood carver. You can't make up for blade geometry.

And for those that haven't tried the 45 deg angle cutting up cardboard that he mentioned, it is a game changer. You don't need to go running for a Chaparral when you only have a Shaman on you.

[Evil D]

Also I forgot to mention this cut was made against the flutes and through 2 sheets. All things considered it would have been easier to cut with the flutes but again if you had to do it this way, a thinner blade is best.

[JRinFL]

Grab a K series kitchen knife, if you have one, and see how well it cuts compared to any of your pocket knives. Folding pockets knives are always compromise, as we all know. Sometimes knives with the best geometry are the least easy to carry. I have a giant CS folder that slices really well because of the surprisingly good geometry of the tall blade. One of my best cardboard terminators.

[yablanowitz]

Hollow grind blades, especially hollow saber grind blades, tend to do the same thing. People seem to think "hollow grind = thin behind the edge = better cutter", none of which is automatically true. Hollow grinds *can be* thinner behind the edge, but mostly they aren't. And even if it is thinner there, a low saber grind usually erases that advantage on a cut more than a half-inch deep.

[TkoK83Spy]

It's not the knife, it's that high quality cardboard!

[JRinFL]

It's not the knife, it's that high quality cardboard!

If you build a better knife, they will build better cardboard?

[Evil D]

It's not the knife, it's that high quality cardboard!

Blasphemer! It's corrugated fiberboard!

[Evil D]

Hollow grind blades, especially hollow saber grind blades, tend to do the same thing. People seem to think "hollow grind = thin behind the edge = better cutter", none of which is automatically true. Hollow grinds *can be* thinner behind the edge, but mostly they aren't. And even if it is thinner there, a low saber grind usually erases that advantage on a cut more than a half-inch deep.

Yep, and even with a true hollow grind, even if it's a full height hollow grind, eventually the full blade stock thickness needs to move through rigid material and that thickness will still matter. For shorter height stuff there is definitely an advantage at least until you hit full stock thickness.

[Bill1170]

When I waved my FFG Endura it noticeably improved the performance in greenery and corrugated fiberboard, because cutting away the spine to form the hook reduced its thickness from 3 mm to 2 mm.

[JRinFL]

It can depend on how the material responds to being cut.

All knives eventually taper to the full thickness of the stock. FFG cross section is a wedge, HHG is a curved sided wedge, like some axes. Flat sided with parallel sides might be the most efficient, but then everything would look even more like a cheap steak knife than they do now.

[dsvirsky]

Was just experiencing this very phenomenon the other day. My new Kershaw Launch 13 feels, to my fingers, like it's ground about as thin as my my HAP40 Delica wharncliffe, but between its greater blade thickness (3.1mm vs 2.5mm) and saber grind that's only about ⅔ as tall as the Delica's full flat grind, the Launch 13 wedges in corrugated fiberboard where the Delica sails rght through.

[yablanowitz]

It can depend on how the material responds to being cut.

All knives eventually taper to the full thickness of the stock. FFG cross section is a wedge, HHG is a curved sided wedge, like some axes. Flat sided with parallel sides might be the most efficient, but then everything would look even more like a cheap steak knife than they do now.

Not true. Some step up to full stock thickness at the plunge grind. You see it a lot on older traditionals, especially multi-blade models. Often the tang is the only part left full thickness. Oddly enough, those thin blades cut with much less effort than modern "tacticool" knives, but they don't make good crowbars.

[Brock O Lee]

Cutting at an angle to the material is a good trick to know about. I've learnt it here years ago. It works on rigid materials like cardboard, hard platics etc. It makes the thicker blades much more versatile because you can eliminate the binding.

[Doc Dan]

I like thinner blades. The SAK is a marvelous cutter for that reason. I have long wanted Spyderco to give us thinner blades, not very wide ones. A little width, sure, but thin for the win. I just said in another thread that I would like to see a Pingo style knife or a larger Jester style with a thin blade and thin behind the edge. That would be the ultimate pocket companion.

[Wartstein]

Great thread!

Just what I always try to say in multiple posts and forms already:
- Thinner blade stock is really great and just slices better, thick stock practically never needed in folders and the tasks (even "harder" ones) people do with folders.

- My main example: Chaparral.
2mm blade, great platform for slicing, still strong enough for even the "hardest" folder tasks I do (also due to the pretty "stout" / "blunt" tip (by profile when looking at the flat of the blade))
I´d still love to see that "Chaparral XL", so basically a longer, Endela / PM2 sized 2mm ffg folder (see here viewtopic.php?t=85342#p1377379) - I think such a knife would suit Spyderco as a performance oriented company well.

- Also "typical" comparisons like Para 3 vs Delica : The Delica almost just has to win as a cutting tool - 2.5 mm ffg stock vs 3.7 mm (almost 50 % thicker) on a small knife is no doubt a better starting point for making a knife a good slicer

- I´d really love to hear examples (there might very well be some, don´t get me wrong) where the 2.5 mm of a Delica or the 2.00 mm of a Chaparral actually HAD been to thin and a blade broke because of its thinness (in any more or less reasonable folder task)
I often think people just find thick blades more confidence inspiring (understandably), but don´t actually know or have tried if a thinner, in cutting better performing blade would be enough.

[Wartstein]

.......
Anyway just something fun I thought we could chat about. I'm really curious about the HP Delica and how that blade is going to be ground. I will always love my Shaman and big beefy knives but the other end of the spectrum is sure a lot of fun to play with.

Btw, David, can´t recall if you actually ever tried a Chaparral - ?

Now that you tend to carry smaller folders (due to your new job I guess) I think you might really like it. No other Spydie out there with 2mm (and ffg!) stock as far as I know.

[Evil D]

.......
Anyway just something fun I thought we could chat about. I'm really curious about the HP Delica and how that blade is going to be ground. I will always love my Shaman and big beefy knives but the other end of the spectrum is sure a lot of fun to play with.

Btw, David, can´t recall if you actually ever tried a Chaparral - ?

Now that you tend to carry smaller folders (due to your new job I guess) I think you might really like it. No other Spydie out there with 2mm (and ffg!) stock as far as I know.

No I don't have one yet, I'm holding out for a serrated one that may never happen. For now my thin options are usually a Dragonfly and today I'm carrying my Centofante 4, which despite being only 2mm thick and a hollow grind, it could be thinner behind the edge to slice better.

[Wartstein]

.......
Anyway just something fun I thought we could chat about. I'm really curious about the HP Delica and how that blade is going to be ground. I will always love my Shaman and big beefy knives but the other end of the spectrum is sure a lot of fun to play with.

Btw, David, can´t recall if you actually ever tried a Chaparral - ?

Now that you tend to carry smaller folders (due to your new job I guess) I think you might really like it. No other Spydie out there with 2mm (and ffg!) stock as far as I know.

No I don't have one yet, I'm holding out for a serrated one that may never happen. For now my thin options are usually a Dragonfly and today I'm carrying my Centofante 4, which despite being only 2mm thick and a hollow grind, it could be thinner behind the edge to slice better.

Well, at least Sal said he is testing a serrated Chap, about a year ago (last sentence of the post viewtopic.php?f=2&t=80989&start=60#p1613132).

The DFly has thicker stock than the Chap - and good thing: If the Dfly grip is ok for your hand, the Chaps should be anyway!