Does thickness matter more than overall volume?

[Mister Coffee]

Batoning? Scandi grinds? I'm blaming this mess on the Scandinavians. They're all treacherous. Well, maybe not Elke Sommer. Actually, she was German, not Scandinavian. But I like to think of her as Scandinavian. Norwegian, maybe. She was always cute in that way that just made you feel better when everything went all to hell. But, um, perhaps I digress . . . .

 

[not2sharp]

Seriously? Here are my candid thoughts.

It's a knife. It cuts stuff. I don't mix mathematics with my knife-related tasks. I use whatever knife has proven to be the best tool for the task at hand, and go with that. No algebra, calculators or slide rules required.

No offense intended, but you are trying to apply Einsteinian analytics to a caveman tool, and I don't see the value in it.

Yeah, we should test the blade geometry in a wind tunnel and check for proper harmonics….

n2s

 

[Alberta Ed]

Math stinks.

 

[DangerZone98]

from my point of view, a Scandi is too close to a saber grind to make an interesting comparison. Be of more interest if you compared Full Flat Grind (FFG) to a saber or scandi.

There's a lot of "internet authorities" who promote the use of FFG for every use. It's hard to obtain anything other than a FFG from some manufacturers. FFG is great for slicing. But I prefer scandi or saber for what I perceive to be the increased strength.

Hi. Bit off topic, but what is your take on hollow grinds? They cut extremely well in my experience, but is there a noticable drop in durability compared to saber?

 

[DangerZone98]

Might be some poor math. If that's the case, hopefully someone who's less mathematically challenged than me could fix this equation.

For years I've liked saber-grinds for batoning. One of my assumptions was thicker blades of the same material/heat treat/etc... were by definition stronger. But then it dawned on me I didn't know the overall volume and a thinner blade with more material might be stronger. The crux of this theory is people often look at thickness of a blade and discount the triangle-ish (I know they all aren't perfectly flat nor symmetrical) shape at the bottom. The thickness argument should only be true if we were dealing with two rectangles of different thicknesses. So I took some of my blades and measured them to come up with two theoretical knives and calculate the volume or rather amount of metal used. Both blades will be 1.25 inches in height. The scandi-grind will be 5/32 thick and the saber-grind will be 3/16 or rather 6/32 thick. Length of blade will be discounted and assumed to be the same length. I've converted some of the common fractions we use to make the equations easier to work with. Please feel comfortable with correcting any mistakes.

Scandi 1.25 inches height (or 40/32)
- 5/32 Thick * 32/32 height = 160/32 .... 32/32 represent 1in worth of flat before the blade begins to taper.
- Blade taper; 5/64 (half base) * 16/64 (height) = 80/64 or 40/32 ... Both my scandi-grinds have about .25in in taper.
- Total = 200/32

Saber 1.25 inches height
- 6/32 (or 3/16) * 12/32 (or 3/8) height = 72/32
- Blade taper; 3/32 (half base) * 28/32 height = 84/32
- Total = 156/32

Assuming this is a fair estimate, there's still a problem. In my testing, thicker blades allow for less strikes in batoning. This means the potential increase in durability from a scandi-grind would need to out weigh the increase in strikes. What are your thoughts on all this?

If we want to eliminate the thickness factor, then we need to test for two knives with the same thickness then, or at least they need to be as close as possible. But great idea, man.

 

[DangerZone98]

If the discussion involves batoning and strength then I assume the question is which shape will be stronger with respect to lateral bending.

This isn't easy to explain so I'll try not to make this too long. Volume is not the correct measure of the strength of a cross section, you need to calculate a property called section modulus. Section modulus has to do with how far the material is from the center of the cross section. There aren't a lot of variables in blade shapes so volume will follow closely with section modulus. A scandi or saber grind has more of the blade that is full thickness, so more of the material is farther out from the centerline of the blade and this would be stronger. FFG takes some outside material off and becomes a triangle, the material that was removed was farthest from the center of the blade so reduces its strength quite a bit. A hollow grind removes even more material from the outside of the blade and makes this the weakest with respect to lateral bending. Now if you took a thick blank and made a FFG blade that weighed as much as a scandi, it would be thicker at the spine and very well could be stronger due to having some material much farther out from the center of the blade.

I'm discussing strength with respect to lateral bending of the blade which I think will generally control for most situations but anything can happen. Now consider a blade like the Cold Steel SRK- it is fairly thick at the spine but the blade isn't real tall. If you had a taller blade like a typical chef knife you might say it would be stronger when if you put the edge on a log and hit the tip with your baton and to some extent this is correct. However it is hard to do this and not have some amount of lateral bending at the same time. If you could load a blade vertically like this then yes the thinner blade that is taller would be stronger than the thicker blade that is not that tall.

I love how unapologetically thick the SRKs and Recon Tantos are, lol.

 

[Londinium Armoury]

How did Darth Vader lose his hand?
He was the first Jedi to baton with his sabre.

 

[DMG]

Hi. Bit off topic, but what is your take on hollow grinds? They cut extremely well in my experience, but is there a noticable drop in durability compared to saber?

This is ancedotal like most data on the ‘net but I tortured buck hollow ground fixed blades and folders as a boy scout and never hurt them.

 

[me2]

If you want to make a comparison here you will have to decide which dimensions to hold constant. Blade width, spine thickness, cross sectional area (which I think you are calling volume).

A blade 1” wide and 1/4” thick with a full flat grind is very close to the same cross section as a 1/8” thick blade with just a sharpened edge (Scandi grind). They behave very differently in different situations. Lateral strength will go to the flat ground blade. Cutting ability will go to the Scandi blade I think, but I’d have to test and it depends on the depth of the cut. I’d baton the 1/4” blade with much less reservation.

 

[Dergyll]

From me owning and using knives of different grinds, as well as my perceived "feel" of it going through/into peop- I mean, stuff:

Best use:
Flat - cardboard, boxes (ENDURA)
Hollow - small food, delicate stuff (CIVIVI)
Convex - wood (dont like it for anything else really) (BARK RIVER)
Scandi - wood? Cans? (MORA)
Saber - not sure what it is

Only knives I've ever broken are a SAK (wedged it something and couldn't get it out) and an old rapala fillet knife (sat on it), which are both atypical of what a knife should be used for.

I'm Asian and I hate math.

 

[Londinium Armoury]

It's easy to do the math on this, different grinds offer better or worse toughness in varying portions of the blade.
For example a scandi is thinner directly behind the edge, than a FFG blade with secondary bevel say for general purpose sake 20 degree angle. So the scandi being more accute directly at the edge, this means it is less tough than the knife with secondary bevel. This is only accounting for the apex area and steel directly behind the apex at lower edge angle.
Then the Scandi quickly becomes thicker than the FFG when you move further back. This can apply to a grind like a convex round (but stiull zero without secondary bevel) like a Katana grind. Where right directly at and behind the apex is actually thinner than a FFG blade with secondary bevel. But it quickly becomes thicker and due to convex axe like structure beefs up the Niku or meat of thickness.
Then you have the middle of the blades to compare, not at the spine and not at the edge, there are many wedge like shapes that are slightly thicker or thinner at this section. You have to compare like you say overall volume and mass contributing to the entire blade structure.
So if you were to compare all blade shapes and compare them for toughness. It's not just spine thickness, or edge angle of apex to consider.
A blade with the toughest grind yet best ability to seperate wood is a felling axe wedge shape, with a robust convex grind without secondary bevel.
I have done testing on blade shape and geometry of chopping blades for over 4-5 years now constantly making prototypes.
I made a knife that according to my test data was the toughest and most robust geometry. The knife is basically an axe with a knife handle. It is 8mm thick at the spine. Has a zero ground convex edge that leads up to a mid sabre grind. It basically has the geometry somewhat in the middle of a thick Niku Katana and a felling axe.

 

[NeedItCheaper]

If the discussion involves batoning and strength then I assume the question is which shape will be stronger with respect to lateral bending.

This isn't easy to explain so I'll try not to make this too long. Volume is not the correct measure of the strength of a cross section, you need to calculate a property called section modulus. Section modulus has to do with how far the material is from the center of the cross section. There aren't a lot of variables in blade shapes so volume will follow closely with section modulus. A scandi or saber grind has more of the blade that is full thickness, so more of the material is farther out from the centerline of the blade and this would be stronger. FFG takes some outside material off and becomes a triangle, the material that was removed was farthest from the center of the blade so reduces its strength quite a bit. A hollow grind removes even more material from the outside of the blade and makes this the weakest with respect to lateral bending. Now if you took a thick blank and made a FFG blade that weighed as much as a scandi, it would be thicker at the spine and very well could be stronger due to having some material much farther out from the center of the blade.

I'm discussing strength with respect to lateral bending of the blade which I think will generally control for most situations but anything can happen. Now consider a blade like the Cold Steel SRK- it is fairly thick at the spine but the blade isn't real tall. If you had a taller blade like a typical chef knife you might say it would be stronger when if you put the edge on a log and hit the tip with your baton and to some extent this is correct. However it is hard to do this and not have some amount of lateral bending at the same time. If you could load a blade vertically like this then yes the thinner blade that is taller would be stronger than the thicker blade that is not that tall.

Great post, but I need graphics to comprehend this (will probably get more memes with pies). When you said "taller", did you mean longer or a greater height, height being the distance between the edge and the spine while length is the distance between handle butt and tip. And when you said "tip", all I could picture was standing a knife on the handle butt and striking down on the tip of the blade. Would you clarify?

If you want to make a comparison here you will have to decide which dimensions to hold constant. Blade width, spine thickness, cross sectional area (which I think you are calling volume).

A blade 1” wide and 1/4” thick with a full flat grind is very close to the same cross section as a 1/8” thick blade with just a sharpened edge (Scandi grind). They behave very differently in different situations. Lateral strength will go to the flat ground blade. Cutting ability will go to the Scandi blade I think, but I’d have to test and it depends on the depth of the cut. I’d baton the 1/4” blade with much less reservation.

Yes, it is in fact cross sectional area I was referring to. Thank you for the correction. The constant would be blade height. And there'd have to be two tests; one with the same cross sectional area and one with a larger cross sectional area on the scandi blade (but thinner spine).

 

[Mikel_24]

When you batton stuff you got to think SPLITTING MAUL, not AXE. Therefore, more obtuse geometry will always work better. There is a compromise between the ease of penetration/splitting and the force required to exert on the spine and how much the knife can handle before shattering!

Mikel

 

[me2]

Great post, but I need graphics to comprehend this (will probably get more memes with pies). When you said "taller", did you mean longer or a greater height, height being the distance between the edge and the spine while length is the distance between handle butt and tip. And when you said "tip", all I could picture was standing a knife on the handle butt and striking down on the tip of the blade. Would you clarify?



Yes, it is in fact cross sectional area I was referring to. Thank you for the correction. The constant would be blade height. And there'd have to be two tests; one with the same cross sectional area and one with a larger cross sectional area on the scandi blade (but thinner spine).

There is a point where the thicker spined flat ground blade and the thinner Scandi ground blade are equal regarding lateral stiffness. I suspect it’s something like 1/8” for the Scandi blade and 3/16” for the flat ground blade. However I’d have to do a lot more math than anyone in this thread evidently feels comfortable with to find that value. A moderate amount of math could have cut this thread to maybe a dozen posts but what fun is that.

 

[000Robert]

I have never batoned wood with a knife for the fear of my dad. While he was alive, fear that he would beat the shit out of me. And now that he's gone, the fear that he would come out from the grave and haunt me relentlessly.

 

[115Italian]

A fault to all this is that it’s still theory and hypothetical. Strength in concept, design, thickness calculated on paper will not equal real world strength if the heat treat is bad.

 

[bikerector]

Hi. Bit off topic, but what is your take on hollow grinds? They cut extremely well in my experience, but is there a noticable drop in durability compared to saber?

In short, yes, all other things being equal. You're more likely to have a large chip out from a hollow grind than a sabre grind. Having said that, some of the thicker hollow grinds from cold steel, vs buck who do a very slicey hollow, have held up really well for me and I actually quite like them as an all purpose grind favoring slicing over robustness. Cold steel's hollow grinds are pretty shallow, at least on the 3 or 4 that I've had.

 

[rhino]

If the discussion involves batoning and strength then I assume the question is which shape will be stronger with respect to lateral bending.

This isn't easy to explain so I'll try not to make this too long. Volume is not the correct measure of the strength of a cross section, you need to calculate a property called section modulus. Section modulus has to do with how far the material is from the center of the cross section. There aren't a lot of variables in blade shapes so volume will follow closely with section modulus. A scandi or saber grind has more of the blade that is full thickness, so more of the material is farther out from the centerline of the blade and this would be stronger. FFG takes some outside material off and becomes a triangle, the material that was removed was farthest from the center of the blade so reduces its strength quite a bit. A hollow grind removes even more material from the outside of the blade and makes this the weakest with respect to lateral bending. Now if you took a thick blank and made a FFG blade that weighed as much as a scandi, it would be thicker at the spine and very well could be stronger due to having some material much farther out from the center of the blade.

I'm discussing strength with respect to lateral bending of the blade which I think will generally control for most situations but anything can happen. Now consider a blade like the Cold Steel SRK- it is fairly thick at the spine but the blade isn't real tall. If you had a taller blade like a typical chef knife you might say it would be stronger when if you put the edge on a log and hit the tip with your baton and to some extent this is correct. However it is hard to do this and not have some amount of lateral bending at the same time. If you could load a blade vertically like this then yes the thinner blade that is taller would be stronger than the thicker blade that is not that tall.

You're tweaking at brain cells that haven't been touched since I was a sophomore in Mechanics of Materials class back in the mid 1980s! I remember we had to calculate Area Moment of Inertia when studying bending. How is the section modulus related to Area Moment of Inertia?

 

[bikerector]

@NeedItCheaper one thing to consider when batoning, the edge does very little work when splitting wood. It created the initial penetration and then the rest of the work is done but the cheeks of the knife. There are a few anti-batoning videos showing how you can pretty easily baton with a butter knife. The thing with batoning to split wood is you're using the thickness to force the pieces apart so the the thicker blades help spread the wood faster than a thinner grind.

As far as strength goes, I've batoned a lot of knives and never broken one. This includes folders, slipjoints, thin hollow grinds, and thicker knives actually built to do this type of work long-term like Busse's, bushcraft knives, and what I like to call woods or camp knives because I'm not heading to the woods to try and get into a survival situation. Thicker blades, like some of the obscenely thick Busse's at 0.30" thick or more split really well... they just suck at cutting. There's more to it than just spine thickness but you get the point I think.

As far as your math goes, I think @bdmicarta did a pretty good job explaining the problem using volume as some type of measure for strength. We could take to the extremes, and infinitely thin blade that's infinitely tall (edge to spine) to get the desired volume and it would not do well batoning. You could use a thin kitchen knife if you wanted as an example, very thin and tall and could have a similar volume of a less tall but thicker blade. The problem with the kitchen knife is any side loading is going to cause it to bend drastically and could cause a break but it would also not lever the wood pieces apart. A better example might be a machete because people actually baton machete... not the best but it does the job. Going the other way, a really short in height blade that's little more than a wedge probably won't do you a favors either as it won't resist the vertical loads as well. In use, I've found the short in height blades are just annoying to use as they seem really prone to vibrations and shock. Trying to use a short sword, like a swamp rat rucki, as a golok was not enjoyable.

 

[Boombats]

My unscientific / nonmathematical take: saber grinds are good for batonning because they are the most obtuse wedge in comparison to other grinds. Now you say "but Scandi" and I say "but show me an average Scandi knife and an average saber ground blade, and I bet you the saber is thicker." Thickness=better for splitting wood, and that's for 2 reasons. 1, wedgieness. 2, resilience to the baton. Compare a Recon Tanto to a Mora or other common Scandi knife and you can see what's better to whack on with a club.

Thank you for coming to my TEDx talk.