Does thickness matter more than overall volume?

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NeedItCheaper

Joined
Jun 17, 2012
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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?
 
First, I need to check that I've understood where this is going. The idea is that a thinner, but Scandi-beveled knife, should cut deeper, because it has more volume?

Batoning is about your ability to hit the wood with more force than the amount of force that holds the wood together. You could use a filet knife to baton, if you had miraculous materials science standing behind you.

When you talk about thicker blades needing fewer strikes to do the job, I think what you're seeing is the fact that a thicker blade pushes the wood apart further, each time you hit it.

I don't think that the total volume of steel present has anything to do with splitting efficiency. To make it a fair test, you would need to test Scandi and saber grinds at the same stock thickness, with the same force, in (as close to) the same material.
 
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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.
 
The interesting thing about a true Scandinavian knife is that the blade tends to be thinner stock than what you see on a lot of American designs. But because of the grind they use, it is my opinion that you get the same strength.
 
NeedItCheaper said:
What are your thoughts on all this?
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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.
 
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shane45-1911 said:
I like pie. :)
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i-like-turtles-zombie-kid.gif
 
shane45-1911 said:
No offense intended, but you are trying to apply Einstein analytics to a fundamental caveman tool, and I don't see the value in it.
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Yeah, but it's been raining for 3 days now and I had to cut my backpacking trip short because it was too overwhelming. I'm stuck inside and clearly have too much time on my hands.

knarfeng said:
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.
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Your wish is my command

FFG 1.25 inches height
- 6/32 (or 3/16)
- Blade taper; 3/32 (half base) * 40/32 height = 120/32
- Total = 120/32

I wonder if FFG with the same dimensions would literally be 40% less strong. 120/200 = .6

Edit; Yes I edited this immediately after posting.
 
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NeedItCheaper said:
Yeah, but it's been raining for 3 days now and I had to cut my backpacking trip short because it was too overwhelming. I'm stuck inside and clearly have too much time on my hands.
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My first post came across rather harsh, and I do apologize.

I am just not sure there is even an answer to your question, as there are too many variables that your testing probably did not account for. What media were you cutting? How could you be sure you were using the same amount of cutting force/pressure/angle on each stroke, with each knife? How are you maintaining consistency in this to arrive at any meaningful conclusion?

Put another way, I can cut a branch with a butter knife in one stroke (or baton, if you will) if I apply enough force. Likewise, I can cut that same branch with a Scandi, full flat, saber (or insert your grind of choice here) profile with less force, but it has very little to do with thickness and even less to do with volume.

Sheer force trumps all, sometimes.
 
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Shorttime said:
First, I need to check that I've understood where this is going. The idea is that a thinner, but Scandi-beveled knife, should cut deeper, because it has more volume?
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I've kept out discussion of deeper cuts to make this overly complicated thread simpler. A thinner blade cutting deeper isn't part of my argument, only that I've heard many times that thicker means more durable and it doesn't appear to be the case here. If someone enjoys the increase in cutting/carving efficiency of a thinner blade, but are worried about the decrease in durability, they might be worrying about nothing.

Shorttime said:
When you talk about thicker blades needing fewer strikes to do the job, I think what you're seeing is the fact that a thicker blade pushes the wood apart further, each time you hit it.
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Yes, I was making no claim other than this.

Shorttime said:
I don't think that the total volume of steel present has anything to do with splitting efficiency. To make it a fair test, you would need to test Scandi and saber grinds at the same stock thickness, with the same force, in (as close to) the same material.
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Never said it did, why would you assume this was the case? It's about width, not volume. As to the second point, it's fair. But my point was about durability and thickness vs volume. I should do a test of the same thickness comparing saber-grind to scandi. Thank you for taking this more seriously than others. I know it's a complicated post, but just because it's entertaining to post memes about pies, doesn't mean it's wrong.
 
Google “wedge mathematics”.

“A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six simple machines .... The more acute, or narrow, the angle of a wedge, the greater the ratio of the length of its slope to its width, and thus the more mechanical advantage it will yield. A wedge will bind when the wedge included angle is less than the arctangent of the coefficient of friction between the wedge and the material.”

So there. Meaning for tougher wood, say wet hickory, a smaller angle is better. Then again, since we are talking about a knife there will be a trade-off with friction/binding on the blade surface. For easy to split wood, say dry pine, the larger the angle, the better. :)

Hope you get out soon !

Roland.
 
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.
 
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